geotechnical eng. lab manual

CVEN365 Introduction to Geotechnical EngineeringLABORATORY MANUAL

Giovanna BiscontinTexas A&M University

January 19, 2007

2 CVEN365 Laboratory Manual

G. Biscontin Civil Engineering Department

Contents

1 Lab Safety and Policy 1

2 Determining Water Content of Soil Specimens 32.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Water Content by Microwave Oven Method. . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2.1 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2.2 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 32.2.3 Test Specimen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2.4 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2.5 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 Water Content by Oven Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3.1 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3.2 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 62.3.3 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3.4 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Particle Size Analysis of Soils 93.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.3 Particle size analysis of coarse grained fraction. . . . . . . . . . . . . . . . . . . . . . . . 9

3.3.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 93.3.2 Test Sample. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.3.3 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103.3.4 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

3.4 Particle size analysis of fine grained fraction. . . . . . . . . . . . . . . . . . . . . . . . . . 113.4.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 113.4.2 Hydrometer Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.4.3 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123.4.4 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

4 Atterberg Limits: Liquid Limit, Plastic Limit, and Plasticity Index of Soils 194.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194.3 Determination of Liquid Limit (Multi-Point Method). . . . . . . . . . . . . . . . . . . . . 19

4.3.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 194.3.2 Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204.3.3 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204.3.4 Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

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4.4 Determination of Plastic Limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.4.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 224.4.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

4.5 Plasticity Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

5 Classification According to USCS 255.1 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255.2 Initial Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

5.2.1 Highly Organic Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255.2.2 Non Highly Organic Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

5.3 Procedure for Classification of Fine Grained Soils. . . . . . . . . . . . . . . . . . . . . . 265.4 Procedure for Classification of Coarse Grained Soils. . . . . . . . . . . . . . . . . . . . . 27

6 Visual Classification of Soils 296.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296.3 Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296.4 Descriptive Information for Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306.5 Procedure for Identifying Fine-Grained Soils. . . . . . . . . . . . . . . . . . . . . . . . . 316.6 Identification of Inorganic Fine-Grained Soils. . . . . . . . . . . . . . . . . . . . . . . . . 326.7 Procedure for identifying Coarse-Grained Soils. . . . . . . . . . . . . . . . . . . . . . . . 336.8 Check List For Description Of Soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7 Compaction Using Standard Effort 377.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377.3 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377.4 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

7.4.1 Specimen preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387.4.2 Compaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

7.5 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

8 Measuring Suction with the Filter Paper Method 438.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438.2 Soil Suction Concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438.3 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458.4 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .458.5 Soil Matric Suction Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468.6 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .478.7 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

9 Hydraulic Conductivity 499.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .499.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .499.3 Fundamental Test Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 499.4 Constant head test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

9.4.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 499.4.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.4.3 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51


CONTENTS iii

9.5 Falling head test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

9.5.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 52

9.5.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

9.5.3 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

10 Flow Nets 5710.1 Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

10.2 Flow Net Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

10.3 Drawing Flow Nets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

10.4 Rules for Sketching Flow Nets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

10.5 Common Mistakes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

10.6 Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

10.7 Example Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

11 Plaxis exercise 1: Groundwater calculation 6111.1 Groundwater calculations for an embankment. . . . . . . . . . . . . . . . . . . . . . . . . 61

11.1.1 Case 1: uniform embankment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

11.1.2 Initial conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

11.1.3 Case 2: Zoned embankment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

11.1.4 Case 3: anisotropic conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

12 State of Stress: Mohr’s Circle 6712.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

12.2 Two-Dimensional States of Stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

12.3 Mohr’s Circle of Stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

12.3.1 The Pole Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

12.4 Principal Stresses and Principal Planes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

12.5 Mohr’s Circles of Total and Effective Stress. . . . . . . . . . . . . . . . . . . . . . . . . . 70

13 Instrumentation and Calibration 7513.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

13.2 Transducers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

13.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

13.3.1 Calibration Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

13.4 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

14 Shrink/Swell Test 8114.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

14.2 Apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

14.3 Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

14.4 Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

14.5 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

14.5.1 Shrinkage Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

14.6 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

Texas A&M University G. Biscontin

iv CVEN365 Laboratory Manual

15 One-Dimensional Consolidation 8715.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8715.2 Standard Reference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

15.2.1 Required Materials and Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . 8815.3 Specimen Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8815.4 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8915.5 Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9015.6 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

16 Plaxis exercise 2: consolidation settlements calculation 9316.1 Consolidation settlements of an embankment during construction and after completion. . . 93

16.1.1 Input of geometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9316.1.2 Input of material parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9416.1.3 Generation of new mesh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9716.1.4 Initial conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

16.2 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

17 Direct Shear Test of Soils Under Consolidated Drained Conditions 10117.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10117.2 Terminology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10117.3 Apparatus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10117.4 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10217.5 Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10317.6 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

18 Triaxial Unconfined Compression Test 10718.1 Purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10718.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

18.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10718.2.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108

18.3 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10918.4 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109

19 Unconsolidated Undrained Triaxial Test 11119.1 Specimen preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

19.1.1 Preparation of the specimen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11119.1.2 Fitting end caps and membrane. . . . . . . . . . . . . . . . . . . . . . . . . . . .111

19.2 Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11219.3 Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11319.4 Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113

A CVEN 365 Laboratory Design Project 115A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115A.2 Report Submissions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

A.2.1 Data laboratory reports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115A.2.2 Design reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

A.3 Project overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117A.4 Part I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120A.5 Part II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121


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A.6 Part III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122A.6.1 Planned Construction Sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . .122A.6.2 Construction Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122A.6.3 Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124A.6.4 Laboratory Test Interpretation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .125


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Chapter 1

Lab Safety and Policy

Safety is a primary concern in all of the CE Department Geotechnical Engineering laboratories. Both theUndergraduate laboratory (RM-117) and Graduate laboratory (RM-116D) are outfitted with equipment thatcould cause injury if one is not alert while performing experiments. Following is an outline of general policyand ”Do’s and Don’ts” in these laboratories. Safety is everyone’s concern.

1. No food or drink is allowed in the laboratories.

2. Ovens:

• The large ovens in both rooms are set at 105 degrees C. Use properly insulated gloves to handleobjects you are retrieving out of the oven. The gloves are placed near the oven for this purpose.Please return the gloves to the table by the oven.

• The microwave ovens are used for moisture determination in SOILS ONLY. Never place morethan ONE soil sample at a time (in its aluminum dish) in a microwave oven during this process.Check that a heat sink (in the form of a ceramic bowl) is in the microwave to avoid explosions.

3. There are two fire extinguishers in the Undergraduate laboratory and one extinguisher in the Graduatelaboratory. Please observe the mounting locations on the walls and make a mental note of their access.

4. Safety glasses are in a large white cabinet on the north wall of the Undergraduate Laboratory. Shouldone need to use a hammer or blunt instrument to break up dried soil samples then all persons of thelaboratory group will be required to wear safety glasses during this process, including the teachingassistant.

5. Each lab island has a sink with two faucets. One faucet provides hot and cold tap water and is used forcleanup only. The other faucet has a white button on it and is labelled ”DW” (distilled water).

6. During some sessions noise from machinery (such as sieve shakers) may get loud. If this becomesa problem, please notify the teaching assistant and ear protection will be provided on an as-neededindividual basis.

7. Barrels are provided for used soil when the experiment is completed. Never throw trash (foil cups,paper, plastic, etc.) in these barrels. There are trash bins provided for the garbage.

8. At the end of each lab session always clean all the instruments and other materials used. A paper toweldispenser hangs on the wall for cleanup.

9. Counterbalanced Load Frames:


• There are four double load frames in the Undergraduate laboratory and two double load framesin the Graduate laboratory. These frames are safe to operate when using the correct procedure.Never touch these frames when not in use.

• When using the loading frames:

– Never have your head under the top counterweight. The weight may fall while makingadjustments to the set up. This typically occurs at least once a semester. You want to makesure the weight does not fall on you, and especially your head.


Chapter 2

Determining Water Content of SoilSpecimens

2.1 Purpose

The water (or moisture) content of a soil is recorded in every test in geotechnical engineering. This basictype of information provides insight on the conditions of the soil. The water content of undisturbed samplesfrom the site is also measured and reported on boring logs and in the engineering reports. Sometimes, weneed to mix a soil to a certain water content to meet specifications for construction.

Traditionally, we used a standard oven set at a temperature of 110oC. These days we can also use amicrowave oven, which gives immediate results. The two methods are only slightly different and they areboth explained in this chapter. You will mostly use the microwave oven method, but in a few cases thestandard method is more reliable. The instructions for the specific test will tell you which method to use foreach laboratory experiment.

2.2 Water Content by Microwave Oven Method

This method is commonly used as a quicker alternative to the standard oven drying method, therefore it ismostly used when immediate results are needed. You cannot use the microwave oven method for soils withsignificant levels of organics.

The main problem with using the microwave oven for water content determination is the possibilityof heating the soil to temperatures higher than 110o C. The higher temperature may actually change thechemical structure of the clay minerals (think about pottery) and give wrong results. By drying the soil inseveral steps you minimize the chance of overheating.

2.2.1 Standard Reference

ASTM D 4643- Standard test method for determination of water (moisture) content of soil by the microwaveoven heating.

2.2.2 Required Materials and Equipment

The following items will be required for this testing method:

• A microwave oven. Variable power controls are important and reduce the potential for overheating thetest specimen.


• A scale having a 2000 g or greater and readability of 0.1 g is required.

• Specimen container suitable for use in a microwave. These containers must be dry.

• Gloves or holders to handle hot containers.

• Heat sink, something that will absorb the microwave energy once all the water has been extracted fromthe specimen and will prevent overheating.

• Tools such as knives or spatulas for cutting the specimen before and during testing.

2.2.3 Test Specimen

Select the minimum mass of soil to use for moisture content determination based on the following table:

No more than 10% of sample 90% or more of sample Recommended mass ofmade of particles larger than: passes sieve moist specimen

(mm) No. (g)2.0 10 100 to 2004.75 4 300 to 500

19 mm 3/4 in 500 to 1000

Table 2.1: Minimum mass of specimen

2.2.4 Procedure

It is important to prepare the specimen as quickly as possible to minimize moisture loss that will result inthe wrong water content measurement. Break up the soil into small size pieces. If the specimens cannot betested immediately, store them in a sealed container to prevent loss of moisture.

1. Make sure you have a copy of the appropriate moisture content determination form ready for use. Youcan find it at the end of this chapter.

2. Determine the mass of a clean, dry container or dish, and record it.

3. Place the soil specimen in the container, and immediately determine and record the total mass.

4. Place the soil specimen in the container in a microwave oven with the heat sink and turn the oven onfor 3 min.

5. After the set time has elapsed, remove the container and soil from the oven taking care not to burnyourself, and immediately record the mass.

6. Mix the soil carefully with a small spatula, make sure you do not lose any soil.

7. Return the container and soil to the oven and reheat for 1 min.

8. Repeat step 5 through 7 until the change in the measured mass becomes insignificant on the calculatedmoisture content. A change of 0.1% or less of the initial wet mass of the soil should be acceptable formost specimens.

9. Use the final mass determination in calculating the water content.


2. Determining Water Content of Soil Specimens 5

2.2.5 Calculations

Calculate the Water content of the sample as follows:

w =Mcws −Mcs

Mcs −Mc× 100 =

Mw

Ms× 100 (2.1)

where:

w = water content, %

Mcws = mass of container and wet specimen, g

Mcs = mass of container and oven dry specimen, g

Mc = mass of container, g

Mw = mass of water, g and

Ms = mass of solid particles.

Moisture Content Determination by Microwave Oven

Sample No. B-24 Project

Boring No. 12-L Location

Depth 2.4 m

Description of sample Brown silty clay

Date 09/05/03 Tested by Jane Doe

Mass of container,Mc (g) 20.0After 3min.

After 1moremin.

After 1moremin.

After 1moremin.

After 1moremin.

Initial mass of container + wet specimen,Mcws (g) 155.0 155.0 155.0 155.0 155.0Mass of container + dry specimen,Mcs (g) 131.8 122.3 121.5 121.3 121.2Mass of water,Mw = Mcws −Mcs (g) 23.2 32.7 33.5 33.7 33.8Mass of solid particles,Ms = Mcs −Mc (g) 111.8 102.3 101.5 101.3 101.2Moisture contentw = Mw

Ms× 100% (%) 20.75 31.96 33.00 33.27 33.39

Percent difference in water content (%) – 11.21 1.04 0.27 0.12

Figure 2.1: Example of water content by microwave oven calculation

2.3 Water Content by Oven Method

Drying takes at least 12 hours in a standard oven, but the temperature is constant avoiding problems withoverheating. If you have a large sample, overheating is likely in a microwave oven, therefore the standardoven is recommended.



2.3.1 Standard Reference

ASTM D 2216 - Standard test method for laboratory determination of water (moisture) content of soil androck by mass.


The following items will be required for this testing method:

• A drying oven at a temperature of 110oC±5oC.

• A scale with readability of 0.01 g is required for specimens with mass of less than 200 g.

• Specimen container suitable for use in an oven. For small samples (less than 200 g) use the aluminumcontainers with a lid to prevent moisture loss before drying and moisture gain from the air after drying.The containers must be dry.

• Gloves or holders to handle the container.

• Tools such as knives, or spatulas.

• A marker, if the container does not have an identifying feature.

2.3.3 Procedure

1. Make sure you have a copy of the appropriate moisture content determination form ready for use.

2. Determine the mass of a clean, dry container or dish, and record it. Remember to record the containerID or mark the container. Many similar containers are placed in the oven at the same time and may bemoved. You want to make sure you will be able to find your specimen.

3. Place the soil specimen in the container, and immediately determine and record the total mass.

4. Place contained and soil specimen in the oven for at least 12 hours. Longer drying times will notcompromise the results.

5. After the set time has elapsed, remove the container and soil from the oven taking care not to burnyourself, and immediately record the mass.

6. Calculate the water content.

2.3.4 Calculations

Follow the same procedure as above in section2.2.5.


2. Determining Water Content of Soil Specimens 7

Moisture Content Determination by Microwave Oven

Sample No. Project

Boring No. Location

Depth

Description of sample

Date Tested by

Mass of container,Mc (g)After 3min.

After 1moremin.

After 1moremin.

After 1moremin.

After 1moremin.

Initial mass of container + wet specimen,Mcws (g)Mass of container + dry specimen,Mcs (g)Mass of water,Mw = Mcws −Mcs (g)Mass of solid particles,Ms = Mcs −Mc (g)Moisture contentw = Mw

Ms× 100% (%)

Percent difference in water content (%) – –

Moisture Content Determination by Oven

Sample No. Project

Boring No. Location

Depth


Date Tested by

Mass of container,Mc (g)Initial mass of container + wet specimen,Mcws (g)Mass of container + dry specimen,Mcs (g)Mass of water,Mw = Mcws −Mcs (g)Mass of solid particles,Ms = Mcs −Mc (g)Moisture contentw = Mw

Ms× 100% (%)


Chapter 3

Particle Size Analysis of Soils

3.1 Purpose

The particle size distribution of a soil (also called a gradation curve) is primarily used for classificationpurposes. The distribution of particle sizes larger then 0.075 mm (retained on the No. 200 sieve) is deter-mined by sieving, while distribution of particles sizes smaller then 0.075 mm is determined by sedimentationprocess using a hydrometer.

3.2 Standard Reference

ASTM D 422 - Standard test method for particle-size analysis of soils.

3.3 Particle size analysis of coarse grained fraction


• A scale sensitive to 0.01 g

• Sieves, bottom pan, and a lid (The table below provides a list of common sieve sizes)

• Mechanical sieve shaker

Sieve No. Opening (mm)4 4.7510 2.0040 0.42580 0.180100 0.150200 0.075

3.3.2 Test Sample

The size of the sample (i.e., the amount of soil) will depend on the maximum size of the particles present inthe sample itself, according to the following table:


Nominal diameter of Approximate Minimumlargest particles Mass of Portion

in. (mm) g3/8 (9.5) 5003/4 (19.0) 10001 (25.4) 2000

1.5 (38.1) 30002 (50.8) 40003 (76.2) 5000

3.3.3 Procedure

1. Clean each sieve to remove any soil left over from previous tests. Use the soft brush on the finer meshsieve and the wire brush on the coarser mesh sieve. Take care not to damage the mesh.

2. Measure and record the mass of each sieve, including the bottom pan.

3. Obtain the appropriate amount of sample.

4. Weigh and record the mass of the sample selected.

5. Assemble the sieves in order from largest to smallest so that the coarsest is at the top and the finest ison the bottom followed by the pan.

6. Place the sample on to the top sieve taking care not to lose any of the mass and place the lid securelyon top.

7. Place the set of sieves in the sieve shaker and adjust the clamps to secure the sieves.

8. Set the shaker on high and set the timer to five minutes.

9. Remove the sieves from the sieve shaker

10. To insure that all the particles passed though the appropriate sieve, tap each sieve over a sheet of paper,starting with the top sieve. Put any material that falls on to the paper into the next sieve and repeat theprocess with the next sieve.

11. Measure and record the mass retained in each sieve.

12. Sum the mass of the material retained on each sieve to verify that there has been no change in the totalmass of the sample. (Note: A mass loss of less than 2% is acceptable.)

3.3.4 Calculations

• Determine the weight of soil that is retained on each sieve,Wi.

• Calculate the percent of soil that is retained on each sieve (%Ri):

%Ri =Wi

W× 100 (3.1)


3. Particle Size Analysis of Soils 11

• Calculate the percent passing each sieve (%Pi):

%Pi = 100−i∑

k=1

%Ri (3.2)

• Plot the percent passing values on the grain size analysis chart provided.

3.4 Particle size analysis of fine grained fraction


• Stirring apparatus.

• Hydrometer, type 151H or 152H.

• Sedimentation cylinder, glass cylinder marked for a volume of 1000 ml.

• A solution of 40 g/l solution of sodium hexametaphosphate (or Calgon) in distilled water is used as adispersing agent and will be provided

• Thermometer, accurate to 1oF (0.5oC).

• Graduated beaker to 250 ml capacity.

• Timer.

3.4.2 Hydrometer Calibration

The specific gravity of the solution of water and dispersing agent is higher than the specific gravity of distilledwater. This difference must be accounted for when using the equations for percentage of soil remaining insuspension in section3.4.4, which were developed for distilled water. In addition, the hydrometers werecalibrated at a constant temperature of 68oF (20oC), which cannot be ensured in our laboratory. Finally,hydrometers are graduated by the manufacturer to be read at thebottom of the meniscus formed by theliquid on the stem. However, given the difficulty of conducting a reading at the bottom of the meniscusthrough the soil-water suspension, the readings should be taken at thetop of the meniscus and then corrected.The combined amount of the corrections for these three items is calledcomposite correctionand should bedetermined before or while conducting the actual test.

For convenience, measurement of the composite correction can be made at a few different temperaturesspanning the range expected during the test, and the result graphed. The correction for intermediate temper-atures can be estimated using a linear approximation.

Calibration procedure

1. In a graduate cylinder, mix 125 ml of the 40 g/l solution of sodium hexametaphosphate (or Calgon)and then distilled water up to 1000 ml.

2. Allow the temperature of the solution to become in equilibrium with the temperature in the room.

3. Place the hydrometer in the solution, allow to adjust to the temperature and stop moving.

4. Read the hydrometer at thetop of the meniscus formed on the stem.



5. The composite correction for hydrometer 151H is the difference between this reading and one; forhydrometer 152GH it is the difference between the reading and zero.

6. Repeat the measurement in parallel with your hydrometer measurements in the soil-water-dispersingagent mix, when the room temperature changes.

3.4.3 Procedure

1. Obtain the equivalent of 50 g of air dried soil from the material passing the #200 sieve (do not ovendry the soil).

2. Determine the hygroscopic water content (due to humidity in the air) using an additional 10-15 g ofsoil.

3. Mix the soil to a thick slurry using 125 ml of the distilled water-dispersing agent solution.

4. Mix the slurry in a stirring apparatus for 60 seconds.

5. Transfer to the sedimentation cylinder and fill with distilled water up to the 1000 ml mark.

6. Mix thoroughly: cover the sedimentation cylinder mouth using a rubber glove and your hand and turnthe cylinder upside down and back for 1 minute.

7. Set the cylinder down and quickly start the timer. Take readings using the hydrometer at 4, 15, 30, 60,90, 120 seconds. Be careful in inserting the hydrometer, so that it will be stabilized as soon as possibleand leave in the suspension for the first 2 minutes. Take readings at thetop of the meniscus.

8. Repeat the mixing process and take a second set of readings for the first 2 minutes.

9. Remove the hydrometer from the suspension and place with a spinning motion in a cylinder filled withdistilled water. To take the following readings, carefully place the hydrometer in the suspension about20-25 s before the reading is due.

10. Take readings at 5, 15, 30, 60, and 1140 minutes. Place the hydrometer into the distilled water imme-diately after each reading. After each reading, take the temperature of the suspension by inserting thethermometer into the suspension.

11. At the end of the experiment, obtain the final dry weight of soil.

3.4.4 Calculations

Hygroscopic correction factor

Determine the hygroscopic correction factor based on the determination of the hygroscopic water contentresults:

HygroscopicCF =Ws

Wt(3.3)

where:Ws is the weight of the soil after oven drying andWt is the initial weight of the air dry sample.



Diameter of soil particles

The diameter of the soil particles is calculating according to Stoke’s law, assuming that the particles arespherical, and measuring the density of the suspension:

D =

√18ηL

(Gs −G1)ρwT(3.4)

where:

µ = viscosity of water (10.09 millipoise at 20oC)

L = depth at which the density of the suspension is being measured (that is, where the center of gravityof the hydrometer is). See appendix for values ofL given hydrometer reading.

ρw = unit weight of water

Gs = specific gravity of the solid particles

G1 = specific gravity of the solution (usually assumed to be 1)

T = elapsed time

For convenience, the above calculations can be simplified as follows:

D(mm) = K

√L

T(3.5)

where:K is a constant that depends on temperature and specific gravity of the solid particles, given inthe appendix.

Percentage of soil in suspension

Calculate the (oven) dry weight (W) of the soil by multiplying the air-dry weight of the soil to be used in thehydrometer analysis by the hygroscopic correction factor.

The percentage of soil remaining in suspension at the level at which the hydrometer is measuring thedensity is calculated differently for the two hydrometers.

For Hydrometer 151H:

P =100, 000

W

Gs

Gs −G1(Rh −G1) (3.6)

For Hydrometer 152H:

P =Rhα

W× 100 (3.7)

where:

P = percentage of soil remaining in suspension at the level at which the hydrometer is measuring

Rh = corrected hydrometer reading

W = weight of the oven dry soil, after hygroscopic correction

Gs = specific gravity of the solid particles

G1 = specific gravity of the dispersing solution (usually 1)

α = correction factor, see appendix



Sieve Analysis of Coarse FractionSample No. Project

Boring No. Location

Depth


Date Tested by

Total weight of sample

Sieve No. Weight ofSieve

Weight ofSieve + Soil

Weight of SoilRetained

PercentageRetained

PercentagePassed

(g) (g) (g) (%) (%)

Total weight of soil (g)



Hyd

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Ana

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ate

Test

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Sam

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No.

Pro

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Bor

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Dep

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(A)

Hyg

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wat

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t(1

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)M

ass

cup

+so

il(a

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ass

cup

+so

il(o

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dry)

(5)

Mas

sof

wat

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ass

ofso

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ven

dry)

(7)

Mas

sof

soil

(air

dry)

(8)

Hyg

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wat

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fact

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(B)

Hyd

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Ana

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ydro

met

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Soi

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Mas

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soil

Cal

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Tim

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ime

Act

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eter

Rea

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orre

ctio

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Cor

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part

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,DP

erce

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(rh)

(Rh)

(deg

rees

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(mm

)(%

)


Chapter 4

Atterberg Limits: Liquid Limit, PlasticLimit, and Plasticity Index of Soils

4.1 Purpose

The liquid limit, plastic limit, and the plasticity index of soils are used extensively to correlate with engi-neering behavior such as compressibility, hydraulic conductivity, shrink-swell, and shear strength. Atterbergdefined four possible states of consistency for soils: liquid, plastic, semi-solid and solid. The liquid limitdivides the plastic and liquid states and is defined as the water content at which the soil flows to close astandard size groove when shaken in a standardized device. At this water content the soil has an approximateshear strength of 2.5 kPa. The plastic limit separates plastic and semi-solid states. At water contents belowthe plastic limit the soil cannot be molded without cracking.


ASTM D 4318 - Standard test method for liquid limit, plastic limit, and plasticity index of soils.

4.3 Determination of Liquid Limit (Multi-Point Method)


• Liquid limit device cup

• Grooving tool

• 200-250 g of soil passing the No. 40 sieve, 425µm aperture size

• Scale with accuracy of 0.001 g

• Water content cup

• Spatula and mixing tools


Figure 4.1: Procedure for adjusting the liquid limit device.

4.3.2 Preparation

Inspection of Wear

Clean the liquid limit device and make sure it is in good working order. The results of the test will beincorrect if the device is not working properly. In particular, check for:

• signs of wear on the base where the cup makes contact. The worn spot should be no greater than10mm (38 in.) in diameter.

• wear on the rim of the cup (reduced to no less than half its original thickness). and in the center wherethe groove is dug into the soil (indentation should be less than 1mm or 0.004 in.).

• side to side movement of the cup should be less than 3mm (18 in.).

• the cup should not drop before the cup hanger loses contact with the cam

• excessive wear of the grooving tool

If your liquid limit device is not in good order please alert your laboratory instructor to obtain a newliquid limit device.

Calibration

It is very important to calibrate your device so that the drop height is correct. The wrong drop height willcause the test results to be incorrect.

Adjust the height of drop of the cup so that the point on the cup that comes in contact with the base risesto a height of 10± 0.2 mm. Place a piece of masking tape across the contact spot on the bottom of the cupand running parallel to the hinged side. Slide the height gage (usually at the end of the grooving tool) underthe cup. The gage should touch both the cup and the tape (see fig.4.1). If the drop height is correct youshould hear a clicking sound, but produce no motion when cranking the handle. Adjust as needed.

4.3.3 Procedure

Soils should be tested starting from the natural water content to ensure the results are more representative ofthe actual field conditions. In our laboratory we will be using air dried samples because it is easier to storethe soil and ensure a constant supply.


4. Atterberg Limits: Liquid Limit, Plastic Limit, and Plasticity Index of Soils 21

The liquid limit is defined as the water content at which a standard groove cut in the remolded soil sampleby a grooving tool closes over a length of 13 mm (0.5 in) at exactly 25 blows of the liquid limit cup fallingfrom a height of 10 mm on a hard rubber base. It is very difficult to mix the soil at the right water content,even after a number of trials. However, if different trials are plotted on a semi-logarithmic scale they shouldlie on a straight line and the liquid limit could be taken as the value of water content where the line crossesthe 25 blows mark. For this reason, in a liquid limit test we try to mix the soil at least three different watercontents aiming at blow counts above and below 25.

1. Mix the soil thoroughly with enough distilled water to reach a consistency requiring about 25 to 35blows of the liquid limit device to close the groove. This is about the consistency of creamy peanutbutter. Keep in mind that it is easier to add water than to take it away, so try to aim for the “thicker”consistency.

2. Using a spatula, place a portion of the prepared soil in the cup of the liquid limit device at the pointwhere the cup rests on the base, squeeze it down, and spread it into the cup to a depth of about 10 mmat its deepest point, tapering to form an approximately horizontal surface. Take care to eliminate airbubbles from the soil pat, but form the pat with as few strokes as possible. Keep the unused soil in themixing/storage dish. Cover the dish to retain the moisture in the soil.

3. Form a groove in the soil pat by drawing the tool, beveled edge forward, through the soil on a linejoining the highest point to the lowest point on the rim of the cup. When cutting the groove, hold thegrooving tool against the surface of the cup and draw in an arc, maintaining the tool perpendicular tothe surface of the cup throughout its movement.

4. Verify that no crumbs of soil are present on the base or the underside of the cup. Lift and drop the cupby turning the crank at a rate of approximately 2 drops per second until the two halves of the soil patcome in contact at the bottom of the groove along a distance of 13mm (1

2 in).

5. Record the number of drops, N, required to close the groove.

6. Quickly remove a slice of soil approximately the width of the spatula, along the groove and includingthe portion of the groove in which the soil flowed together, place in a container of known mass, andobtain a water content. Try to determine water content as soon as possible. The sample is small andlooses water quickly through evaporation.

7. Return the soil remaining in the cup to the mixing cup. Wash and dry the cup and grooving tool andreattach the cup to the carriage in preparation for the next trial.

8. Remix the entire soil specimen in the dish adding distilled water to increase the water content of thesoil and decrease the number of blows required to close the groove.

9. Repeat steps 1-8 for at least two additional trials producing successively lower numbers of blows toclose the groove. One of the trials shall be for a closure requiring 25 to 35 blows, one for closurebetween 20 and 30 blows, and one trial for a closure requiring 15 to 25 blows.

4.3.4 Calculation

• Plot the relationship between the water content,wn, and the corresponding number of drops, N, on thegraph provided. Draw the best straight line through the three or more plotted points.

• Take the water content corresponding to the intersection of the line with the 25-drop abscissa as theliquid limit of the soil and round to the nearest whole number. Computational methods may be substi-tuted for the graphical method for fitting a straight line to the data and determining the liquid limit.



4.4 Determination of Plastic Limit


• Ground glass plate

• Metal rod, 3.2 mm diameter

• Balance

• Water content cup

4.4.2 Procedure

1. Select about 20 g of soil from the material prepared for the liquid limit test.

2. Reduce the water content of the soil to a consistency at which it can be rolled without sticking to thehands by spreading or mixing on the glass plate.

3. From this plastic limit specimen, select a 1.5 to 2.0 g portion. Form the selected portion into a ball.

4. Roll the mass between the palm or fingers and the glass plate to form a thread of uniform diameterthroughout its length. Keep rolling until the thread reaches 3.2 mm (1

8 in) diameter. Compare to themetal rod to determine if the diameter is 3.2 mm. The process should take no more than 2 minutes foreach thread.

5. When the thread has reached a 3.2 mm diameter, break it into pieced and knead together in a ball.Repeat the rolling and kneading process until the thread crumbles and the soil can no longer be rolledinto a 3.2 mm thread. Do not cheat, be consistent: apply the same rolling pressure during each stage ofthe rolling and do not pretend to roll while you wait for the soil to dry and crumble. If the soil breaksinto threads of shorter length, roll each of these shorter pieces into threads 3.2 mm in diameter andrepeat the kneading and rolling process.

6. Collect the broken pieces in a water content cup and cover to prevent further drying while rolling thenext 1.5-2.0 g of soil.

7. Select another 1.5 to 2.0 g portion of soil from the plastic limit specimen and repeat the operationssteps 3-6 until the container has at least 6g of soil.

8. Use the 6 g of soil to obtain the water content according to the procedures in chapter2.

9. Go through the procedure in steps 1-8 until you have obtained two 6 g samples and water contentvalues. The water contents should not have a difference of more than 1.4%. The plastic limit is theaverage of the two water content values.

4.5 Plasticity Index

Calculate the plasticity index as follows:

PI = LL− PL (4.1)

where:


4. Atterberg Limits: Liquid Limit, Plastic Limit, and Plasticity Index of Soils 23

LL = liquid limit

PL = plastic limit



Atterberg Limits Determination

Sample No. ProjectBoring No. LocationDepthDescription of sampleDate Tested by

Liquid Limit Determination

Can No.Mass of can (g)Mass of wet soil + can (g)Mass of dry soil + can (g)Mass of dry soil (g)Mass of water (g)Water content, (%)No. of drops

LIQUID LIMIT =PLASTIC LIMIT =PLASTICITY INDEX =

Plastic Limit Determination

Can No.Mass of can (g)Mass of wet soil + can (g)Mass of dry soil + can (g)Mass of dry soil (g)Mass of water (g)Water content, (%)


Chapter 5

Classification of Soils According to theUnified Soil Classification SyStem (USCS)

The Unified Soil Classification System (USCS) is based on the classification scheme developed by ArthurCasagrande for the United States Army in the 1940’s. In its simplest form, it consists in assigning a two- orfour-lettergroup symbolto the soil sample.

5.1 Definitions

• fines: soil particles passing the #200 sieve (nominal diameter smaller than 0.075mm).

• Coefficient of uniformity:Cu = D60D10

.

• Coefficient of curvature:Cc = Cz = D230

D10D60 .

• Plasticity Index: PI = LL-PL.

5.2 Initial Classification

5.2.1 Highly Organic Soils

Organic soils are recognized by:

• large presence of organic materials;

• dark brown, dark gray or black color;

• organic odor, especially when wet

• very soft consistency

In this case, the material is classified as a peat, with symbol PT, and no further analysis is necessary.


5.2.2 Non Highly Organic Soils

1. Determine gradation curve by sieve analysis. Use only the material with size smaller than 3in (75mm).But report the percentage (by weight) of these large particles.

2. If the soil contains less than 5% fines a detailed sieve analysis is required to estimate the values of thecoefficient of uniformity,Cu, and the coefficient of curvature,Cc or Cz.

3. If the soil contains between 5% and 12% fines, the liquid limit and the plastic limit of the fines shouldbe determined, in addition to the detailed gradation curve andCu, Cc.

4. If the soil contains more than 12% fines the liquid limit and the plastic limit of the fines should bedetermined, but it is sufficient to estimate the percentage of soil in the sand and gravel range. Thegradation characteristics,Cu andCc, are not required.

5.3 Procedure for Classification of Fine Grained Soils

Follow this procedure if 50% or more by weight passes the #200 sieve. This is equivalent to saying that 50%or more by weight has a nominal diameter smaller than 0.075mm.

Figure 5.1: Plasticity chart (from ASTM Standard D2487).

1. Calculate the plasticity index (PI).

2. Compare with the plasticity chart:

• LL>50 and PI>”A” line ⇒ High plasticity clay (CH)

• LL>50 and PI<”A” line ⇒ High plasticity silt (MH)

• LL<50 and PI>”A” line ⇒ Low plasticity clay (CL)

• LL<50 and PI<”A” line ⇒ Low plasticity silt (ML)

• In the shaded area with 16<LL<25-30 and 4<PI<7 above the ”A” line⇒ Silty clay (CL-ML)


5. Classification According to USCS 27

• If the soil has organic content: refer to ASTM standard D2487 on the proper procedure. In short,you need to oven dry the specimen to eliminate the organic material and calculate the LL on theoven dried specimen. The classification is based on the difference between the LL before andafter oven drying.

3. You can add more information on the soil specimen classification after the main group symbol.

• If 15% to 30% of the soil had nominal diameter larger than 0.075mm, use⇒ with sand or withgravel, depending on which is predominant.

• If 30% to 50% of the soil had nominal diameter larger than 0.075mm, use⇒ sandy or withgravelly, depending on which is predominant.

5.4 Procedure for Classification of Coarse Grained Soils

Follow this procedure if 50% or more by weight is retained by the #200 sieve. This is equivalent to sayingthat 50% or more by weight has a nominal diameter larger than 0.075mm.

1. >50% of the specimen is retained on the #4 sieve (nominal diameter larger than 4.75mm)⇒ Gravel(G)

• If <5% fines andCu ≥ 4 and1 ≤ Cc ≤ 3 ⇒ Well-graded gravel (GW)

• If <5% fines andCu ≤ 4 and/or not1 ≤ Cc ≤ 3 ⇒ Poorly-graded gravel (GP)

• If 5% < fines < 12% and the fines are clay⇒ Well-graded gravel with clay (GW-GC) orPoorly-graded gravel with clay (GP-GC) based onCu andCc tests above.

• If 5% < fines < 12% and the fines are silt⇒ Well-graded gravel with silt (GW-GM) orPoorly-graded gravel with silt (GP-GM) based onCu andCc tests above.

• If >12% fines and fines are clay based on plasticity chart⇒ Clayey gravel (GC)

• If >12% fines and fines are silt based on plasticity chart⇒ Silty gravel (GM)

• If >12% fines and fines are CL-ML based on plasticity chart⇒ Silty clayey gravel (GM-GC)

2. >50% of the specimen is retained between the #4 and the #200 sieves (nominal diameter between0.075 and 4.75mm)⇒ Sand (S)

• If <5% fines andCu ≥ 6 and1 ≤ Cc ≤ 3⇒ Well-graded sand (SW)

• If <5% fines andCu ≤ 6 and/or not1 ≤ Cc ≤ 3 ⇒ Poorly-graded sand (SP)

• If 5% < fines < 12% and the fines are clay⇒Well-graded sand with clay (SW-SC) or Poorly-graded sand with clay (SP-SC) based onCu andCc tests above.

• If 5% < fines < 12% and the fines are silt⇒ Well-graded sand with silt (SW-SM) or Poorly-graded sand with silt (SP-SM) based onCu andCc tests above.

• If >12% fines and fines are clay based on plasticity chart⇒ Clayey sand (SC)

• If >12% fines and fines are silt based on plasticity chart⇒ Silty sand (SM)

• If >12% fines and fines are CL-ML based on plasticity chart⇒ Silty clayey sand (SM-SC)


Chapter 6

Visual Classification of Soils

6.1 Purpose

During drilling and sampling operations in the field classification has to be carried out quickly and withoutgradation analyses or Atterberg limits. An approximate procedure is then used and the description is notedon the boring log. The initial boring log is often checked later in the laboratory with the help of the retrievedsoil samples. Even in the laboratory a small portion of the samples will be actually tested for classificationpurposes. The specimens for classification testing are chosen from the different layers that were identifiedduring field operations and from previous information, where available. The remaining samples are classifiedbased on their similarities in the tested samples and visual-manual procedures illustrated below.


ASTM D2488 - Standard practice for description and identification of soils (visual-manual procedure).

6.3 Terminology

Gravel Particles of rock that will pass a 3 in (75 mm) sieve and be retained on a No. 4 (4.75 mm) sieve withthe following subdivisions:

• coarse - passes 3 in (75 mm) sieve and retained on34 in (19 mm) sieve.

• fine - passes a 3.4 in (19 mm) sieve and retained on a No.4 (4.75 mm) sieve.

Sand Particles of rock that will pass a No. 4 (4.75 mm) sieve and be retained on a No. 200 (75µm) sievewith the following subdivisions:

• coarse - passes a No. 4 (4.75 mm) and retained on No. 10 (2.00 mm) sieve

• medium - Passes a No. 10 (2.00 mm) sieve and is retained on a No. 40 (425µm) sieve.

Silt Soil passing a No. 200 (75µm) sieve that is non-plastic or very slightly plastic and that exhibits little ofno strength when dry. For classifications, a silt is fine grained soil or the fine grained portion of a soil,with a plasticity index less than 4, or the plot of plasticity index versus liquid limit falls below the “A”line.


Clay Soil passing a No. 200 (75µm) sieve that can be made to exhibit plasticity within a range of watercontents, and that exhibits considerable strength when air-dry. For classifications a clay is a finegrained soil or a fine grained portion of a soil, with a plasticity index equal to or greater than 4, andthe plot of plasticity index versus liquid limit falls on or above the “A” line.

Organic Silt A silt with sufficient organic content to influence the soil properties. For classifications, anorganic silt is a soil that would be classified as a silt, except that its liquid limit value after oven dryingis less than 75% of its liquid limit value before oven drying.

Organic Clay A clay with sufficient organic content to influence the soil properties. For classification, anorganic clay is a soil that would be classified as a clay, except that its liquid limit value after ovendrying is less than 75% of its liquid limit value before oven drying.

6.4 Descriptive Information for Soils

Angularity Describe the angularity of the sand (coarse sizes only), gravel, cobbles, and boulders, as angular,subangular, subrounded, or rounded in accordance with the criteria in table6.1. A range of angularitymay be stated, such as subrounded to rounded.

Shape Describe the shape of gravel, cobbles, and boulders as flat, elongated, or flat and elongated if theymeet the criteria if they meet in table6.2. Otherwise do not mention the shape. Indicate the fractionof particles that have that shape; for example: ”one-third of the gravel is flat”.

Color Described the color of the sample when moist.

Odor Describe the odor of the sample if organic or unusual

Moisture Condition Describe the moisture condition as dry, moist, or wet in accordance with the criteriain table6.3

Consistency For intact fine-grained soil, describe the consistency as very soft, soft, firm, hard, or very hardin accordance with the criteria in table6.4. This observation is inappropriate for soils with significantamounts of gravel.

Cementation Describe the cementation of intact coarse grained soil as weak, moderate, or strong, in accor-dance with Table6.5.

Range of particle sizesFor gravel and sand components, described the range of particle sizes within eachcomponents. For example, about 20% fine to coarse gravel, about 40% fine to coarse sand.

Maximum particle size Describe the maximum particle size found in the sample for each size classifica-tion. For example, the largest particle size for sand size particles and the largest particle for gravel sizeparticles.

Description CriteriaAngular Particles have sharp edges and relatively plane sides with unpolished surfaces

Subangular Particles are similar to angular description but have corners and edgesSubrounded Particles have nearly plane sides but have rounded corners and edges

Rounded Particles have smoothly curved sides and no edges

Table 6.1: Criteria for describing angularity of coarse-grained particles.


6. Visual Classification of Soils 31

The particle shape shall be described as follows where length, width, and thickness refer tothe greatness, intermediate, and least dimensions of a particle respectively.

Description CriteriaFlat Particles with width/thickness> 3

Elongated Particles with length/width> 3Flat and Elongated Particles meet criteria for both flat and elongated

Table 6.2: Criteria for describing particle shape.

Description CriteriaDry Absence of moisture, dusty, dry to the touch

Moist Damp but no visible waterWet Visible free water, usually soil is below water table

Table 6.3: Criteria for describing moisture conditions.

Description CriteriaVery soft Thumb will penetrate soil more that 1in. (25mm)

Soft Thumb will penetrate soil about 1in. (25mm)Firm Thumb will indent soil about 1/4in. (6mm)Hard Thumb will not indent soil but will readily intent with thumbnail

Very Hard Thumbnail will not indent soil

Table 6.4: Criteria for describing consistency

Description CriteriaWeak Crumbles or breaks with handling of little finger pressure

Moderate Crumbles or breaks with considerable finger pressureStrong Will not crumble with finger pressure

Table 6.5: Criteria for Describing Cementation

Hardness Describe the hardness of coarse sand and larger particles.

6.5 Procedure for Identifying Fine-Grained Soils

Select a representative sample of the material for examination. Remove particles larger than the No. 40 sieveuntil a specimen equivalent to about a handful of material is available. Use this specimen for performing thedry strength, dilatancy, and toughness test.

Dry Strength Select a few dry lumps of about 1/2in. in diameter. Test the strength of the dry pieces bycrushing between the fingers. Note the strength as none, low, medium, high, or very high in accordancewith the criteria in Table6.6. If natural dry lumps are used do not use the results of any of the lumpsthat are found to contain particles of coarse sand.

Dilatancy From the specimen select enough material to mold into a ball about 1/2in. in diameter. Mole thematerial, adding water if necessary, until it has a soft, but not sticky consistency. Smooth the soil inthe palm of one hand with a small spatula. Shake horizontally, striking the side of the hand vigorouslyagainst the other hand several times. Note the reaction of water appearing on the surface of the soil.



Description CriteriaNone The dry specimen crumbles into powder under mere pressure of handlingLow The dry specimen crumbles into powder with some finger pressure

Medium The dry specimen breaks into pieces or crumbles with considerable finger pressureHigh The dry specimen cannot be broken with finger pressure

Very High The dry specimen cannot be broken with thumb and a hard surface

Table 6.6: Criteria for Describing Dry Strength

Squeeze the sample by closing the hand or pinching the soil between the fingers, and note the reactionas none, slow, or rapid in accordance with the criteria in Table6.7. The reaction is the speed at whichthe water appears while shaking, and disappears while squeezing.

Description CriteriaNone No visible change in specimenSlow Water appears slowly on the surface during shaking and does not disappear or

disappears slowly upon squeezingRapid Water appears quickly during shaking and disappears quickly during squeezing

Table 6.7: Criteria for Describing Dilatancy

ToughnessFollowing the completion of the dilatancy test, the test specimen is shaped into an elongated patand rolled by hand on a smooth surface or between the palms into a thread about 1/8in. in diameter.Fold the threads and reroll repeatedly until the thread crumbles at a diameter of about 1/8in. The threadwill crumble at a diameter of 1/8 in. when the soil is near the plastic limit. Note the pressure requiredto roll the thread near the plastic limit. Also, note the strength of the thread. After the thread crumbles,the pieces should be lumped together and kneaded until the lump crumbles. Note the toughness of thematerial during kneading.Describe the toughness of the thread and lump as low, medium or high inaccordance with the criteria in table6.8.

Description CriteriaLow Only slight pressure is required to roll the thread near the plastic limit. The

thread and lump are soft and weakMedium Medium pressure is required to roll the thread to near the plastic limit. The

thread and lump have medium stiffness.High Considerable pressure is needed to roll thread near the plastic limit. The thread

and lump have very high stiffness

Table 6.8: Criteria for Describing Toughness

Plasticity On the basis of observations made during the toughness test, describe the plasticity of the materialin accordance with the criteria given in Table6.9.

6.6 Identification of Inorganic Fine-Grained Soils

Identify the soil as follows:



Description CriteriaNonplastic A 1/8in. thread cannot be rolled at any water content

Low The thread can barely be rolled and the lump cannot be formed when drier thanthe plastic limit

Medium The thread is easy to roll and not much time is required to reach the plasticlimit. The thread cannot be rolled after reaching the plastic limit. The lumpcrumbles drier than the plastic limit

High It takes considerable time rolling and kneading to reach the plastic limit. Thethread can be rolled several times after reaching the plastic limit. The lumpcan be formed without crumbling when drier than the plastic limit.

Table 6.9: Criteria for Describing Plasticity

Soil Symbol Dry Strength Dilatancy ToughnessML None to Low Slow to rapid Low or thread cannot be formedCL Medium to High None to Slow MediumMH Low to Medium None to Slow MediumCH High toVery High None High

Table 6.10: Identification of Inorganic Fine-Grained Soils from Manual Test

6.7 Procedure for identifying Coarse-Grained Soils

1. The soil is a gravel if the percentage of gravel is estimated to be more than the percentage of sand.

2. The soil is a sand if the percentage of gravel is estimated to be equal to or less than the percentage ofsand.

3. The soil is a clean gravel or clean sand if the percentage of fines is estimated to be 5% of less.

4. Identify the soil as well-graded gravel, GW, or as well-graded sand, SW, if it has a wide range ofparticle sizes and substantial amounts of the intermediate particle sizes.

5. Identify the soil as a poorly graded gravel, GP, or as a poorly graded sand, SP, if it consists predom-inantly of one size (uniformly graded), or it has a wide range of sizes with some intermediate sizesobviously missing.

6. The soil is either a gravel with fines or a sand with fines if the percentage of fines is estimated to be15% or more.

7. Identify the soil as a clayey gravel, GC, or a clayey sand, SC, if the fines have the properties of clays.

8. Identify soil as a silty gravel, GM, or a silty sand, SM, if the fines have the properties of a silt.

9. If the soil is estimated to contain 10% fines, give the soil a dual identification using two group symbols.The first group symbol shall correspond to a clean gravel or sand (GW,GP, SW, SP) and the secondsymbol shall correspond to a gravel or sand with fines (GC, GM, SC, SM).

10. The group name shall correspond to the first group symbol plus the words ”with clay” or ”with silt”to indicate the plasticity characteristics of the fines. For example: ”well-graded gravel with clay,GW-GC” or ”poorly graded sand with silt, SP-SM.”



11. If the specimen is predominantly sand or gravel but contains an estimated 15% or more of the othercoarse-grained constituent, the words ”with gravel” or ”with sand” shall be added to the group name.For example: ”poorly graded gravel with sand, GP” or ”clayey sand with gravel, SC.”

12. If the specimen is predominantly sand or gravel but contains an estimated 15% or more of the othercoarse-grained constituent, the words ”with gravel” or ”with sand” shall be added to the group name.For example: ”poorly graded gravel with sand, GP” or ”clayey sand with gravel, SC.”

13. If the field sample contains any cobbles or boulders, or both the words ”with cobbles” or ”with cobblesand boulders” shall be added to the group name. For example: ”silty gravel with cobbles, GM.”

6.8 Check List For Description Of Soil

1. Group Name

2. Group Symbol

3. Percent of cobbles or boulders, or both

4. Percent of gravel, sand or fines, or all three (by dry weight)

5. Particle size range gravel - fine or coarse, sand - fine, medium or coarse

6. Particle angularity: angular, subangular, subrounded, rounded.

7. Particle shape: (if appropriate) flat, elongated, flat and elongated

8. Maximum particle size dimension

9. Hardness of coarse sand and larger particles

10. Plasticity of fines: nonplastic, low, medium, high, very high

11. Dry strength: none, low, medium, high, very, high

12. Dilatancy: none,slow, rapid

13. Toughness: lox, medium, high

14. Color (in moist conditions)

15. Odor (if unusual or organic)

16. Moisture: dry, moist, wet

17. Consistency (fine-grained soils only): very soft, soft, firm, hard, very hard

18. Cementation: weak, moderate, strong

19. Local name (if any)

20. Geologic interpretation

21. Any additional comments



Classification Data SheetSample Classification Comments


Chapter 7

Compaction Using Standard Effort

7.1 Purpose

Soil placed as engineering fill (embankments, foundation pads, road bases) must be compacted to the se-lected density and water content to ensure the desired performance and engineering properties such as shearstrength, compressibility, or permeability. Also, foundation soils are often compacted to improve their en-gineering properties. Laboratory compaction tests provide the basis for determining the percent compactionand water content needed in the field, and for controlling construction to assure that the target values areachieved.

In a geotechnical laboratory you would prepare at least four (preferably five) specimens with watercontents bracketing the estimated optimum water content. A specimen having a water content close tooptimum would be prepared first by trial additions of water and mixing and then water contents for the restof the specimens would be selected to provide at least two specimens wet and two specimens dry of optimum,and water contents varying by about 2%, but no more than 4%. In this laboratory exercise each group in yoursection will compact one of the specimens at a specific water content, as directed by the laboratory instructor,and the results from all the groups will be combined later.

The data, when plotted, represents a curvilinear relationship known as the compaction curve. The valuesof optimum water content and standard maximum dry unit weight are determined from the compaction curve.

These test methods apply only to soils (materials) that have 20% or less by mass of particles retained onthe No.4 (4.75 mm) sieve.


ASTM D 698 - Standard test methods for laboratory compaction characteristics of soil using standard effort(12,400 ft-lbf/ft3 (600 kN-m/m3)).

7.3 Required Materials and Equipment

• Mold - A cylindrical metal mold having a 4.000± 0.016 in (101.6± 0.4 mm) average inside diameter,a height of 4.584± 0.018 in (116.4± 0.5 mm) and a volume of 0.0333± 0.0005ft3 (944± 14 cm3).

• Rammer - with free fall of 12± 0.05 in (304.8± 1.3 mm) from the surface of the specimen. The massof the rammer is 5.5± 0.02 lbm (2.5± 0.01 kg).

• Sample extruder - A jack for extruding compacted specimens from the mold.


• Balance - with 1 g readability.

• straight edge - for leveling off compacted sample

• mixing tools - for mixing the sample of soil with increments of water.

7.4 Procedure

7.4.1 Specimen preparation

1. Obtain from your laboratory instructor a sample of the soil to be tested. You will need approximately2 kg.

2. Without previously drying the sample, pass it through a No. 4 (4.7 mm) sieve. Determine the watercontent of the processed soil. See chapter2 for the procedure.

3. Double check the target water content for your specimen with the laboratory instructor.

4. Calculate how much water should be added or subtracted from your sample to obtain the desired watercontent. Remember to account for the moisture already present in the sample and use the exact valuefor the mass of the soil, not the approximate number.

5. To add water, spray it into the soil during mixing; to remove water, allow the soil to dry in air at ambienttemperature Mix the soil frequently during drying to maintain an even water content distribution.Thoroughly mix each specimen to ensure even distribution of water throughout and then place in aseparate covered container.

7.4.2 Compaction

1. Determine and record the mass of the mold or mold and base plate.

2. Assemble and secure the mold and collar to the base plate. Place on the concrete floor of the laboratory,NOT on the counters.

3. The specimen is compacted in 3 layers. Remember that after compaction the layers should be approx-imately equal in thickness and the last layer should extend above the top of the mold, but no more than14 in (6 mm). Place approximately 1/3 of the loose soil into the mold for each layer and spread into alayer of uniform thickness.

4. Compact each layer with 25 blows. In operating the manual rammer, do not lift the guide sleeveduring the rammer upstroke. Hold the guide sleeve steady and within 5o of vertical. Apply the blowsat a uniform rate of approximately 25 blows per minute and in such a manner as to provide complete,uniform coverage of the specimen surface. Usually this is achieved by moving the rammer along theperimeter of the mold and using 5 blows to cover the whole area. Then the pattern is repeated for 5times.

5. After compaction of the first two layers, trim any soil remaining on the mold walls or extending abovethe compacted surface and include it with the soil for the next layer. Before placing the next layer ofsoil scarify the surface of the compacted soil with a knife or other suitable tool to avoid separation ofthe layers at the joints later in the test.


7. Compaction Using Standard Effort 39

6. If the third layer extends above the top of the mold by more than14 in (6 mm) or below the top of the

compaction mold, the specimen should be discarded.

7. Following compaction of the last layer, remove the collar and base plate from the mold. A knife maybe used to trim the soil adjacent to the collar to loosen the soil from the collar before removal to avoiddisrupting the soil below the top of the mold.

8. Carefully trim the compacted specimen even with the top of the mold by means of the straightedgescraped across the top of the mold to form a plane surface even with the top of the mold. Initialtrimming of the specimen above the top of the mold with a knife may prevent the soil from tearingbelow the top of the mold. Fill any holes in the top surface with unused or trimmed soil from thespecimen, press in with the fingers, and again scrape the straightedge across the top of the mold.

9. Determine and record the mass of the specimen and mold to the nearest gram.

10. Remove the material from the mold using the sample extruder.

11. Obtain a specimen for water content by using the whole specimen or a representative sample. Select asuitable container and record its weight.

12. Weigh the container and the specimen.

13. Place in the oven for 24 hours. If the entire specimen is used, break it up to facilitate drying.

14. Record the weight of the oven dried specimen in the container.

7.5 Calculations

• Post the following information as directed by the laboratory instructor: laboratory section (week day),group (color), date, mass of moist specimen in the mold, mass of mold, water content determination:mass of moist soil after compaction and can, mass of can, mass of oven dried specimen an can. Seesection7.5for a form to fill.

• Calculate the total unit weight of each specimen:

γt =Mt g

Vm=

(Msm −Mm)gVm

(7.1)

where:

Mt = mass of moist soil

Msm = mass of the moist specimen and mold

Mm = mass of the mold

Vm = volume of the mold (944cm3)

g = acceleration of gravity (9.807m/s2)

• Calculate water content of each compacted specimen:

w =Mw g

Ms g=

(Mwsc −Msc)(Msc −Mc

(7.2)

where:



Mw = mass of water

Ms = mass of dry soil

Mwsc = mass of wet soil and can

Msc = mass of dry soils and can

Mc = mass of can

w = water content

• Calculate dry unit weight:

γd =γt

1 + w(7.3)

• Plot the values and draw the compaction curve as a smooth curve through the points (see example,Fig. 3). Plot dry unit weight to the nearest0.1 lbf

ft3, (0.2 kN

m3 ) and water content to the nearest 0.1 %.

• From the compaction curve, determine the optimum water content and maximum dry unit weight.

• Plot the 100% saturation curve.


7. Compaction Using Standard Effort 41

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Moisture content Determination

Sample No. Project

Boring No. Location

Depth


Date Tested by

Mass of container,Mc (g)After 3min.

After 1moremin.

After 1moremin.

After 1moremin.

After 1moremin.

Initial mass of container + wet specimen,Mcws (g)Mass of container + dry specimen,Mcs (g)Mass of water,Mw = Mcws −Mcs (g)Mass of solid particles,Ms = Mcs −Mc (g)Moisture contentw = Mw

Ms× 100% (%)

Percent difference in water content (%) – –

Group Data SheetGroup Target Water

ContentMoist UnitWeight

Water Content Dry UnitWeight

Dry UnitWeight for100% Sat.

(%) (kN/m3) (%) (kN/m3) (kN/m3)


Chapter 8

Measuring Suction with the Filter PaperMethod

8.1 Purpose

The filter paper method has long been used in soil science and engineering practice and it has recently beenaccepted as an adaptable test method for soil suction measurements because of its advantages over othersuction measurement devices. Basically, the filter paper comes to equilibrium with the soil either throughvapor (total suction measurement) or liquid (matric suction measurement) flow. At equilibrium, the suctionvalue of the filter paper and the soil will be equal. After equilibrium is established between the filter paperand the soil, the water content of the filter paper disc is measured. Then, by using filter paper water contentversus suction calibration curve, the corresponding suction value is found from the curve. This is the basicapproach suggested by ASTM Standard Test Method for Measurement of Soil Potential (Suction) UsingFilter Paper (ASTM D 5298). ASTM D 5298 employs a single calibration curve that has been used to inferboth total and matric suction measurements. The ASTM D 5298 calibration curve is a combination of bothwetting and drying curves. Bulut (2001) demonstrates that the ”wetting” and ”drying” suction calibrationcurves do not match, an observation that was also made by Houston et al. (1994). In this test, the wettingcurve as shown in Figure8.2 is used because the filter paper becomes wet during the test.

8.2 Soil Suction Concept

In general, porous materials have a fundamental ability to attract and retain water. The existence of thisfundamental property in soils is described in engineering terms as suction, negative stress in the pore water.In engineering practice, soil suction is composed of two components: matric and osmotic suction (Fredlundand Rahardjo 1993). The sum of matric and osmotic suction is called total suction. Matric suction comesfrom the capillarity, texture, and surface adsorptive forces of the soil. Osmotic suction arises from thedissolved salts contained in the soil water. This relationship can be formed in an equation as follows:

ht = hm + hπ (8.1)

where:

ht = total suction (kPa)

hm = matric suction (kPa)


hp = osmotic suction (kPa)

Total suction can be calculated using Kelvin’s equation, which is derived from the ideal gas law usingthe principles of thermodynamics and is given as:

ht =RT

Vln

(P

Po

)(8.2)

where:

ht = total suction

R = universal gas constant

T = absolute temperature

V = molecular volume of water

P/Po = relative humidity

P = partial pressure of pore water vapor

Po = saturation pressure of water vapor over a flat surface of pure water at the same temperature.

If equation8.2 is evaluated at a reference temperature of 25o, the following total suction and relativehumidity relationship can be obtained:

ht = 137, 182 ln(P/Po) (8.3)

It can be said, in general, that in a closed system under isothermal conditions the relative humidity maybe associated with the water content of the system such as 100% relative humidity refers to a fully saturatedcondition. Therefore, the suction value of a soil sample can be inferred from the relative humidity andsuction relationship if the relative humidity is known. In a closed system, if the water is pure enough, thepartial pressure of the water vapor at equilibrium is equal to the saturated vapor pressure at temperature, T.However, the partial pressure of the water vapor over a partly saturated soil will be less than the saturationvapor pressure of pure water due to the soil matrix structure and the free ions and salts contained in the soilwater (Fredlund and Rahardjo 1993).

In engineering practice, soil suction has usually been calculated in pF units (Schofield, 1935) (i.e., suc-tion in pF = log10|suction in cm of water|). However, soil suction is also currently being represented inlog(kPa) unit system (Fredlund and Rahardjo 1993) (i.e., suction inlog(kPa) = log10|suction in kPa|).The relationship between these two systems of units is approximately suction inlog(kPa) = suction in pF- 1. Matric suction can be calculated from pressure plate and pressure membrane devices as the differencebetween the applied air pressure and water pressure across a porous plate. Matric suction can be formed in arelationship as follows:

hm = −(ua − uw) (8.4)

where:

hm = matric suction

ua = applied air pressure

uw = free water pressure at atmospheric condition


8. Measuring Suction with the Filter Paper Method 45

The osmotic suction of electrolyte solutions, that are usually employed in the calibration of filter papersand psychrometers, can be calculated using the relationship between osmotic coefficients and osmotic suc-tion. Osmotic coefficients are readily available in the literature for many different salt solutions. Table 1gives the osmotic coefficients for several salt solutions. Osmotic coefficients can also be obtained from thefollowing relationship (Lang 1967):

φ = − ρw

vmwln

(P

Po

)(8.5)

where:

f = osmotic coefficient

v = number of ions from one molecule of salt (i.e.,v = 2 for NaCl, KCl,NH4Cl andv = 3 forNa2SO4,CaCl2, Na2S2O3,etc.)

m = molality

w = molecular mass of water

ρw = density of water

The relative humidity term(P/Po) in eq. 8.5 is also known as the activity of water (aw) in physicalchemistry of electrolyte solutions. The combination of eq.8.2 and eq.8.5 gives a useful relationship thatcan be adopted to calculate osmotic suctions for different salt solutions:

hπ = −vRTmφ (8.6)

8.3 Required Materials and Equipment

• Schleicher & Schuell No. 589-WH filter paper

• Sensitive balance with accuracy of 0.0001 g

• Constant temperature container (or cooler)

• moisture tins and glass jars

• PVC rings, electrical tape

• tweezers and gloves

• Oven and aluminum block

8.4 Procedure

A testing procedure for total suction measurements using filter papers can be outlined as follows:

1. At least 75% by volume of a glass jar should be filled with the soil; the smaller the empty spaceremaining in the glass jar, the smaller the time period that the filter paper and the soil system requireto come to equilibrium.



2. A ring type support, which has a diameter smaller than filter paper diameter and about 1 to 2cm inheight, is put on top of the soil to provide a non-contact system between the filter paper and the soil.Care must be taken when selecting the support material; materials that can corrode should be avoided,plastic or glass type materials are much better for this job.

3. Two filter papers one on top of the other are inserted on the ring using tweezers. The filter papersshould not touch the soil, the inside wall of the jar, and underneath the lid in any way.

4. Then, the glass jar lid is sealed very tightly with plastic tape.

5. Steps 1, 2, 3, and 4 are repeated for every soil sample.

6. After that, the glass jars are put into the ice-chests in a controlled temperature room for equilibrium.

Researchers suggest a minimum equilibrating period of one week (ASTM D 5298; Houston et al., 1994;Lee 1991). After the equilibration time, the procedure for the filter paper water content measurements canbe as follows:

1. Before removing the glass jar containers from the temperature room, all aluminum cans that are usedfor moisture content measurements are weighed to the nearest 0.0001 g. accuracy and recorded.

2. After that, all measurements are carried out by two persons. For example, while one person is openingthe sealed glass jar, the other is putting the filter paper into the aluminum can very quickly (i.e., in afew seconds) using tweezers.

3. Then, the weights of each can with wet filter paper inside are taken very quickly.

4. Steps 2 and 3 are followed for every glass jar. Then, all cans are put into the oven with the lids half-open to allow evaporation. All filter papers are kept at105 ± 5oC temperature inside the oven for atleast 10 hours.

5. Before taking measurements on the dried filter papers, the cans are closed with their lids and allowedto equilibrate for about 5 minutes. Then, a can is removed from the oven and put on an aluminumblock (i.e., heat sinker) for about 20 seconds to cool down; the aluminum block functions as a heatsink and expedites the cooling of the can. After that, the can with the dry filter paper inside is weighedvery quickly. The dry filter paper is taken from the can and the cooled can is weighed again in a fewseconds.

6. Step 5 is repeated for every can.

8.5 Soil Matric Suction Measurements

Soil matric suction measurements are similar to the total suction measurements except instead of insertingfilter papers in a non-contact manner with the soil for total suction testing, a good intimate contact shouldbe provided between the filter paper and the soil for matric suction measurements. Both matric and totalsuction measurements can be performed on the same soil sample in a glass jar as shown in Fig. 1. A testingprocedure for matric suction measurements using filter papers can be outlined as follows:


8. Measuring Suction with the Filter Paper Method 47

Figure 8.1: Assembly for total and matric suction measurements.

8.6 Procedure

1. A filter paper is sandwiched between two larger size protective filter papers. The filter papers used insuction measurements are 5.5cm in diameter, so either a filter paper is cut to a smaller diameter andsandwiched between two 5.5cm papers or bigger diameter (bigger than 5.5cm) filter papers are usedas protection.

2. Then, these sandwiched filter papers are inserted into the soil sample in a very good contact manner(i.e., as in Fig. 1). An intimate contact between the filter paper and the soil is very important.

3. After that, the soil sample with embedded filter papers is put into the glass jar container. The glasscontainer is sealed up very tightly with plastic tape.

4. Steps 1, 2, and 3 are repeated for every soil sample.

5. The prepared containers are put into ice-chests in a controlled temperature room for equilibrium.

8.7 Calculations

After obtaining all of the filter paper water contents, figure8.2 is employed to get total suction and matricvalues of the soil samples.



Figure 8.2: Filter paper wetting calibration curve.

Paper Suction Determination

Sample No. Project

Boring No. Location

Depth


Date Tested by

Total SuctionPaper

Matric SuctionPaper

Container NumberMass of container (g)Mass of wet paper + container (g)Mass of wet filter paper (g)Mass of hot container (g)Mass of dry filter paper (g)Mass of water in filter paper (g)Water content of filter paper (%)


Chapter 9

Hydraulic Conductivity

9.1 Purpose

Hydraulic conductivity is the parameter that tells us how fast water can flow through soil. This quantity ismeasured to determine if a particular soil is a suitable material for a levee, dam or landfill liner, or filter.During this laboratory both the constant head and the falling head methods will be used.


ASTM D 2434 - Standard test method for permeability of granular soils (constant head).

9.3 Fundamental Test Conditions

The following test conditions are prerequisites for laminar flow of water through granular soils, underconstant-head conditions:

• Continuity of flow with no soil volume change during a test.

• Flow with the soil voids saturated with water and no air bubbles in the soil voids.

• Flow is steady state with no change in hydraulic gradients.

• Direct proportionality of velocity of flow with hydraulic gradients below certain values, at whichturbulent flow starts.

All other types of flow involving partial saturation of soil voids, turbulent flow, and unsteady state offlow are transient in character and yield variable and time-dependent coefficients of permeability; therefore,they require special test conditions and procedures.

9.4 Constant head test


• Permeameter - Specimen cylinders with minimum diameter of 8 or 12 times the maximum particlesize. The permeameter should be fitted with a porous disk at the bottom with a permeability greater


Figure 9.1: Schematic of constant head test set-up.

than that of the soil specimen, but with openings small enough to prevent movement of the soil par-ticles. The permeameter should be fitted with manometer outlets for measuring head loss,h, over alength,L, equivalent to at least the diameter of the cylinder.

• Sample - A representative sample of air-dried granular soil containing less than 10% of the materialpassing the No. 200 sieve.

• Constant head board - Board including manometer tubes with scales for measuring head of water anda water reservoir.

• Plastic tubing

• Stopwatch

• Thermometer

9.4.2 Procedure

1. Unscrew the three nuts on the top of the permeameter cell and remove the top. Make sure the #200mesh screen is covering the two ports on the inside middle of the cell.


9. Hydraulic Conductivity 51

2. Place one of the porous stones in the bottom of the cell. Fill the cell with the soil sample. Place theother porous stone on top. The top of this stone should be about 1/4 inch below the top of the cell.

3. Make sure the surface where the O-ring seals off the cell is clean and replace the top. Evenly tighteneach of the nuts on the top of the cell.

4. Connect a tube coming out of the reservoir on the board to the water faucet.

5. Place the other tube coming out of the reservoir over the sink so that water will be allowed to drainout.

6. Connect tubes from points A and B on the permeameter cell to the two manometers. The distancebetween these two points on our sample is 10 cm.

7. Connect a tube from the needle valve on the board to the lower ball valve on the cell.

8. Fill the reservoir with water. Adjust the water tap so that the level in the cup remains the same andwater is draining into the sink. This gives us constant head.

9. Let the water flow slowly from the reservoir, into the cell, through the bottom porous stone, soilsample, top stone, out of the top of the cell. The water will replace the voids within our sample.

10. Get all of the bubbles out of the tubes by tapping them. De-air the lines going to the manometer tubes.Close the top ball valve and open the lower ball valve. Crack the petcock valve to purge out any airbubbles and then close it off.

11. Open the top ball valve on the cell and watch water come out of the top of the cell. The needle valveon the board controls the flow out of the top of the cell.

12. Record the differential reading between the two manometers.

13. Using a beaker, collect 100 mL of water from the water coming out of the top of the cell. Time howlong it takes to get 100 mL using the stopwatch.

14. Repeat this process collecting 200 and then 300 mL of water.

15. Take the temperature of the water in the constant head cup. Our data will only be good for water atthis specific temperature.

9.4.3 Calculations

• Determine the average time it took to collect 100 mL of water.

• Calculate the cross-sectional area of our soil sample. The diameter of the sample is 2.5 in or 6.35 cm.

• Calculate the coefficient of permeability, k.

k =QL

A∆ht(9.1)

Where

Q=volume of water collected

L=sample height



A=cross-sectional area of soil specimen

∆ h=differential reading betweenh0 andh1

t=duration of water collection

• Calculate the corrected k value for the temperature you recorded.

kcorrected = kηTC

η20C(9.2)

9.5 Falling head test


• Permeameter

• Sample - use the same sample prepared for the constant head test

• Calibrated stand pipe

• Plastic tubing

• Calipers

• Stopwatch

9.5.2 Procedure

1. Connect a tube between points A and B on the permeameter cell. We bypass the manometers this time.

2. We have a new sample height for this test. Measure the height using the calipers from the top of thebottom porous stone to the bottom of the top stone.

3. Attach a tube from the top ball valve on the cell to the calibrated stand pipe valve.

4. Open both of these valves.

5. Attach a tube from the water faucet to the lower ball valve on the cell.

6. Let the water flow through the cell, out of the top, and into the stand pipe.

7. Purge any bubbles from the tubes by opening the petcock valve on the permeameter cell.

8. Allow water to flow slowly through the stand pipe and out of the funnel at the top.

9. When there are no more bubbles, disconnect the hose from the faucet and close the ball valve at thesame time.

10. Time how long it takes the water to drop a known distance in the stand pipe.



Figure 9.2: Schematic of falling head test set-up.



9.5.3 Calculations

• Calculate the cross-sectional area of the tube. The inner diameter of the tube is 3/16 in.

• Calculate the coefficient of permeability, k.

k =aL

Atln

h0

h1(9.3)

Where

– a=cross-sectional area of tube

– L=sample height

– A=cross-sectional area of soil specimen

– t=elapsed time

– h0=initial head

– h1=final head

• Calculate the corrected k value for the temperature you recorded using9.2.



Constant Head Data

∆H =L =Temp =

mL Collected Time(s)

Falling Head Data

L =h0=h1 =Temp =

Trial Number Time(s)


Chapter 10

Flow Nets

10.1 Definitions

• Flow net a graphical representation of the2−D flow of water through soils

• Flow line the flow path of a particle of water

• Equipotential line− a line representing constant head

10.2 Flow Net Facts

• The area between two flow lines is called a flow channel.

• The rate of flow in a flow channel is constant.

• The velocity of flow is normal to equipotential lines.

• The difference in head between two equipotential lines is called the potential drop or head loss.

10.3 Drawing Flow Nets

• Identify prefixed conditions, noting starting directions of lines.

• Draw trial family of flow lines (or equipotentials) consistent with prefixed conditions.

• Keeping the lines you just drew, sketch first trial flow net. Make all lines intersect other set of lines at90 degrees.

• Erase and redraw lines until all figures are square. Subdivide as desired for detail and accuracy.

10.4 Rules for Sketching Flow Nets

• Flow lines must intersect equipotential lines at right angles.

• The area between flow lines and equipotential lines must be curvilinear squares. An inscribed circleshould be able to be drawn that touches each side of the square.


Figure 10.1: Budhu, 2000.

Figure 10.2: Cedergren, 1989.


10. Flow Nets 59


• Flow lines cannot intersect other flow lines.

• Equipotential lines cannot intersect other equipotential lines.

• The more flow lines and equipotential lines drawn, the more accurate your results. However, the morelines, the more difficult it will be to draw the flow net. Drawing a few will allow you to obtain asuitable solution.

10.5 Common Mistakes

10.6 Example

10.7 Example Problem




Figure 10.5: Budhu, 2000.


Chapter 11

Plaxis exercise 1: Groundwater calculation

The second phase of the project requires you to evaluate the design of embankment in terms of seepage. Youwill use finite elements to solve Laplace equation for complex boundary conditions and non-homogeneouscross sections.

11.1 Groundwater calculations for an embankment

Start Plaxis 7.2 Professional, Plaxis Input and select “New Project”.

11.1.1 Case 1: uniform embankment

General settings

• In theProject tab sheet, enter “365 Project” in theTitle box.

• In theGeneralbox select thePlane strain modeland15-node elements.

• In theDimensionstab sheet, leave the default units (note: everything is in m, kN, etc..). ForGeometrydimensions, enter: left:0.00, Right=65.00, bottom=0.00, top=16.00. In theGrid section, leave spacingat 1m, but increase the number of intervals to 2. This allows you to “snap-to-grid”. defaults.

• Click OK to confirm.

Input of geometry

Select theGeometry linetool. Use figure11.1 in the next page to construct the geometry of the problem.Note: right click to end a geometry line. Use the selection tool (red arrow) to click and drag on pointsyou want to move or delete. To input coordinates with the keyboard you can click in thePoint number andcoordinatesbar below the drawing area and use the syntax: (x coord. y coord). The geometry line toolmust be selected and you must have a space between the two numbers). You need point 8 because that is thehighest water level impounded.

Input of boundary conditions

Click on thestandard fixitiesbutton. The bottom will be prevented from moving both in the vertical andhorizontal directions, the sides can slide in the vertical direction, but not in the horizontal. The fixitiesappear as green marks at the bottom and sides (see figure11.1).


Point X Y(m) (m)

0 0.0 0.01 61.0 0.02 61.0 8.53 0.0 8.54 10.0 8.55 28.0 14.56 34.0 14.57 52.0 8.58 26.5 14

Table 11.1: Coordinates of the embankment.

Figure 11.1: Geometry input of the embankment.


11. Plaxis exercise 1: Groundwater calculation 63

Input of material properties

In this part you assign the material parameters that describe the response of the soil. You should assignappropriate values forγdry andγwet for both soils. You were supposed to measure the hydraulic conductivityof the sand in last week’s laboratory. Since that did not happen because of “technical problems” results fromprevious tests have been used to estimate the hydraulic conductivity of the clayey sand listed in table11.1.Check that the suggested values fork are indeed appropriate for the materials used in your project. Input allthe remaining parameters according to the table. Notice that you are not going to perform any calculation ofstresses or strains at this time, therefore the stiffness and Poisson’s ratio inputs are inconsequential, as wellas the material model selected.

Follow these steps to create a new data set:

• Click on theMaterial setsbutton.

• Select new. A new window appears.

• General tab: write “clay” in the Identificationbox. Select the linear elastic Material model and thedrained conditions.

• Parameters tab: follow the information on the table. Notice that you only need to inputEref andν.Click OK.

• Repeat the same process for the clayey sand.

• Click on the data set “clay” and drag to the soil cluster (area) in the drawing area and drop it. Thecluster should become of the same color as the data set. Repeat for the sand embankment.

Parameter Clay Sandγdry

γwet

kx 8× 10−5m/day 8× 10−3m/day

ky 8× 10−5m/day 8× 10−3m/day

Eref 30,000kN/m3 40,000kN/m3

ν 0.33 0.33

Mesh generation

In the mesh menuselect grid coarseness: very fine. Generate the mesh. Remember the mesh must begenerated any time changes are made to the geometry. When the mesh appears in a new window you needto click on update to save the new mesh. You may also want to select the embankment cluster (click on itand it should become cross-hatched in red) and select “Refine cluster” in the Mesh menu. The mesh will bere-generated with additional elements added to the embankment. See figure11.2for an example. Note thatyour mesh may be diffrent.

11.1.2 Initial conditions

Once the geometry is defined, the materials selected and the discretization completed, you need to input theinitial conditions. In this case you will only go so far as setting up the pore pressures due to steady-stateseepage through the embankment. Click on the green arrow pointing to “Initial conditions” on the top right.You will be asked about the unit weight of water, you can OK the default.



Figure 11.2: Mesh of the embankment generated by Plaxis.


11. Plaxis exercise 1: Groundwater calculation 65

Figure 11.3: Values of total head for the embankment.

Generation of pore pressures

The geometry should look all gray. If not you need to make sure the “green light” on the left is selected.

• Select theClosed flow boundarytool (vertical black line) and make the bottom of the geometry imper-meable. Click on point 0 and then point 1. Right click to end. Also make the top of the embankmenta closed flow boundary.

• Click on the selection tool (the red arrow) and assign boundary conditions: double click on the differentgeometry lines and assign the head to the end points of the geometry line based on figure11.3.

• Click onGenerate water pressures, the button with blue crosses.

• Select: Groundwater calculation (steady state)

Does the calculation converge? If not, the problem is in the large difference in hydraulic conductivitybetween the two materials, which causes very high exit velocities at the toe of the embankment. This mayeventually erode the embankment and result into serious problems for the stability. In most cases, the prob-lem is solved by adding a drain at the toe of the embankment. A drain is usually designed to attract the flowand it is constructed with less erodible materials. Go back to the geometry input and add a drain at the toeof the embankment. Make the drain 0.5m thick and extend it a small length on either side of the toe (seefigure11.4, but don’t add the core boundaries yet). You need to assign another material set to the drain, usea high hydraulic conductivity, two orders of magnitude larger than the sand’s. The other material parametersare not important for this exercise, so you can use the same as the sand’s. Re-mesh the problem, refining the



Figure 11.4: Geometry of the zoned embankment with the drain.

drain cluster. You want to make sure that the groundwater surface is all inside the embankment and does notcross the slope. This avoids seepage on the side of the embankment and prevents erosion. The calculationsshould converge now.

11.1.3 Case 2: Zoned embankment

In the original design the embankment was to be constructed with a central low hydraulic conductivity coreto minimize the flow. The geometry needs to me modified to include the core. Go back to the geometryinput (red arrow at the top left). You may want to save this new geometry under a different name, in caseyou need to go back to your original problem for more considerations. Repeat all the steps from the previouspart. Remember that the core is supposed to be constructed by compacting the in-situ clay when you assignthe material properties for the new cluster. You will also need to re-mesh the geometry.

11.1.4 Case 3: anisotropic conditions

What happens if the hydraulic conductivity is larger (3 to 10 times) in the horizontal direction than it is inthe vertical direction? This is typically the case in clays.


Chapter 12

State of Stress: Mohr’s Circle

12.1 Purpose

In order to describe the state of stress at a point, it is necessary to characterize both normal and shear stressesacting on any arbitrary plane passing through that point. A three-dimensional state of stress is fully charac-terized by six components (3 normal stresses and 3 shear stresses). In the case of geotechnical engineering,we often limit the analysis to two-dimensional states of stress and strain. Mohr’s circle construction is oneof the simplest methods to examine the state of stress and strain in the soil.

12.2 Two-Dimensional States of Stress

The 2-D state of stress at a point can be represented by the normal and shear stresses acting on the faces ofan infinitesimal plane element, such as that in figure12.1a. The normal stressσxx acts on the plane normalto the x-axis in the direction parallel to the x-axis. The shear stressτxz act on the same plane, but in thedirection parallel to the z-axis. The directions ofσzz andτzx are defined similarly. By equilibrium it followsthatτxz = τzx.

In soils, normal stresses are usually compressive and, by convention, compression is taken as positive(notice that the opposite convention is used in continuum mechanics). Then, stressesσxx andσzz in figure12.1a are positive quantities and the shear stresses are also positive as marked.

If the stressesσxx, σzz, τxz are known, it is possible to calculate the magnitudes of the stresses (σθ, τθ)on some arbitrary plane at an angleθ with the x-axis12.1b.

12.3 Mohr’s Circle of Stress

For the purpose of plotting Mohr’s circles,and for this purpose alone, we adopt the convention that counter-clockwise shear stresses are taken as positive quantities. Thus, the counter-clockwise shear stressτzx infigure12.1a is positive and the clockwise shear stressτxz is negative when constructing the Mohr’s circle infigure12.1c.

12.3.1 The Pole Method

The pole of a Mohr’s circle is a unique point on the Mohr’s circle characterized by an important property:

if a line is drawn through the pole with the direction of any plane in the physical space, itintersects the Mohr’s circle at a point that defines the state of stress on that plane.


Figure 12.1: State of stress in a two-dimensional element and the corresponding Mohr’s circle.


12. State of Stress: Mohr’s Circle 69

Figure 12.2: Principal planes and principal stresses

By reversing the definition we can locate the pole as the intersection of the line representing the physicalplane on which the stresses are acting (line QP or RP) and the Mohr’s circle. Line QP is parallel to the planeon whichσzz andτzx act and is parallel to the x-axis. The point P where the line intersects the Mohr’s circleis the pole, P. Similarly, RP is parallel to the z-axis and it also identifies the pole.

We may now use the pole of the circle to calculate the state of stress on any plane through the material.For example, the normal and shear stresses (σθ, τθ) on the plane inclined at an angleθ to the x-axis. Wedraw a line, PN, trough P inclined atθ with line QP (and the x-axis). The stresses at point N are the stressesacting on that plane.

12.4 Principal Stresses and Principal Planes

The points at which the Mohr’s circle crosses theσ-axis represent planes on which the shear stress is zero andthe normal stress is either a minimum or a maximum. These planes are known asprincipal planesande thecorresponding stresses asprincipal stresses. From the geometry of the Mohr’s circle the principal stressesoccur on two orthogonal planes, therefore the stresses must also be orthogonal (see figure12.2.

In three-dimensional stress analysis there are three principal stresses and three principal planes. Thesewill be denoted byσ1, σ2 andσ3, and it is usual practice to defineσ1 ≥ σ2 ≥ σ3; σ1 is the major principalstress,σ2 is the intermediate andσ3 is the minor.

When the layering of soils is horizontal, the vertical and horizontal stresses (σv, σ′v, σh andσ′

h) areprincipal stresses and the vertical and horizontal planes are principal planes. Since it is an axi-symmetricstate of stress (the horizontal stress is the same independent of the direction in the horizontal plane)σv = σ1

andσh = σ2 = σ3.



12.5 Mohr’s Circles of Total and Effective Stress

So far we haven’t differentiated between total and effective stresses. If the stresses acting on the element infigure12.1are total stresses, the effective stresses can be calculated using the principle of effective stress:

σ′ = σ − u

The effective stress circle has the same diameter of the total stress circle, but it is translated to the left bythe amount of the pore pressure (see figure12.3). By examining the circles, we note that:

σ′θ = σθ − u

τ ′θ = τθ

Thus, for a given state of total stress, changes in pore pressure have no effect on the shear stresses.

Figure 12.3: Mohr’s circles of total and effective stress.



Figure 12.4: Example 1.



Figure 12.5: Example 2.



A loading due to a proposed embankment is estimated to be equivalent to a uniform load of 100kPa as shown in figure12.6. The unit weight of the foundation material is16kN/m3, andKo is 0.5. The water table is at 5m depth.

• Draw the Mohr’s circle for the initial stresses in the soil, before the construction of the embankment.

• Two exiting pipelines run parallel to the embankment at a depth of 3m, as shown in figure12.6. We want tomake sure that the stress increase in the soil due to the construction of the embankment is not going to damagethe pipelines. What is the increase in stresses at A and B? Draw the new Mohr’s circles for both points.

• What is the magnitude and the direction of the principal stresses at point A and B after construction?

Figure 12.6: Schematic of the embankment and location of the pipelines.


Chapter 13

Instrumentation and Calibration

13.1 Purpose

The purpose of this laboratory exercise is to familiarize students with some of the basic instrumentationcommonly used in geotechnical engineering laboratories to measure the mechanical properties of soils. Forthe purposes of this class we will assume that electronic instrumentation is the preferred method for allmeasurements in our experiments and we will familiarize ourselves with how they operate and calibratethem for future usage in our later laboratories.

Typically, the physical quantities that we need to measure when conducting experiments on soils aretemperature, force, displacement, and pressure. The choice of which sensor to use for a particular task, in aparticular situation depends on two main considerations: a) technical characteristics of the sensor; b) a cost-benefit analysis, which includes considerations on ease of use as well. Temperature is the easiest to accuratelymeasure and for all experiments in this lab will be measured with a simple mercury thermometer or a handheld digital thermometer. In many research laboratories the instrumentation is kept at a carefully controlled,constant temperature, because many sensors are sensitive to temperature, even if they are not meant tomeasure it. Commercial geotechnical laboratories are not usually equipped with constant temperature rooms,and the expense would not be justified in normal circumstances.

The experimenter must consider cost, simplicity, technical characteristics and time to decide whetherto use relatively inexpensive instrumentation such as mechanical dial indicator based instruments (for dis-placement and force measurements) and simple pressure gages or the more expensive, more accurate andautomated electronic instrumentation. These days, the cost of electronics is usually not an impediment to theuse of electronic instrumentation for all the measuring needs in a soil mechanics laboratory.

13.2 Transducers

A transducer is a device that converts energy from one form to another. An electronic transducer has eitheran input or an output that is electrical in nature, such as a voltage or a current. In our case, we are interestedin a transducer that senses a physical change (force, displacement, pressure) and converts it to an electricalsignal, directly related to that physical change. We call this type of transducer a sensor. The principle ofelectronic instrumentation is to use an electrical sensor to detect change in a physical quantity and output anelectrical signal to a measuring device. This electrical signal becomes convenient to use as the input signalto a measurement system, such as an elaborate voltmeter, a chart recorder, an oscilloscope, or even better, acomputer that will accumulate all the information over time in memory, so it can be used at a later date. Therelationship between measured output voltage and physical quantity being sensed is the response function,usually expressed in terms of a formula and obtained through a calibration process.


A good example: you are driving a car at the speed indicated on your speedometer. The rotation rate ofthe car’s wheel is detected by a sensor, which outputs a voltage that increases with increasing speed. Youcould then use a digital voltmeter to read the output of the sensor. Obviously, you would get a speeding ticket,because the voltage alone does not tell you the speed. You also need a relationship between measured voltageand speed and, you’d rather see your speed directly in miles/hr. In order to make this conversion to MPHone has to determine the correlation between the sensor’s output voltage and the known speed. Usuallythe voltage is measured at several different speeds in order to maximize the accuracy of the conversionrelationship. Lastly, thanks to the relationship between voltage and speed, the voltmeter can be re-scaled inMPH rather than volts.

In conclusion, we used a sensor to detect a certain physical quantity and then converted the electricalcurrent output from the sensor (through calibration against a known standard) to engineering units that aremore meaningful and useful to us.

In general, when examining the technical characteristics of a sensor we consider:

• Precision, or the ability to detect small changes in the measured quantity reliably, and the ability tomeasure the same value under repeated identical conditions. Example: a typical measuring tape has aprecision of1/4in., because that is the closest distance between two marks.

• Accuracy, the difference between the measured quantity and the ”true” value, as defined by acceptedstandards. Example: when you weigh yourself with a cheap scale the precision may be 1lb, but theneedle indicates a weight that may not be accurate. In fact if you step down and back up the needlewill usually indicate a different weight: the scale is not accurate.

• Range

• Stability

• Noise

• Temperature coefficient

• Linearity error

• Physical ruggedness, and size.

13.3 Calibration

You will calibrate two instruments this week. Both will be used in future laboratories during the rest of thesemester. These instruments are a force transducer and a displacement transducer. Output accuracy of thesetransducers is only as good as the quality of the transducer, accuracy of the standard used in comparison, andthe care taken in calibrating the transducer to the known standard. In this week’s lab we will calibrate boththe force (in N) and displacement transducer (in mm), each to a known physical standard. We will vary thephysical parameters over a known range of the instrument and record the voltage output at each point overthat range. We can then generate a best-fit line through those points by plotting the physical input parameter(mm or N) against the resulting voltage output reading from the transducer. Plot the input parameter inphysical units on the Y axis and the resultant output reading on the X axis. Using any appropriate softwarepackage, determine the best fit to your data. Usually, a linear fit is the most appropriate and will have theform:

Physical Quantity = CF * Output Voltage + ZEROWhere: CF is the calibration factor ZERO, this constant ensures that when the physical quantity is zero

(for example: no force applied) or in the initial position (example: we need to measure the differential


13. Instrumentation and Calibration 77

displacement, not the absolute position) the formula will give a zero reading. Notice that in the case of theforce transducer the ZERO is very important because any error in estimating the ZERO during calibrationresults in an error in our estimate of the applied load. When measuring differential displacement we set theinitial measurement as ZERO, without calibrating the sensor again.

This formula is the response function for the transducer and will be used in the future. Given this formula,we can use the transducer in different experiments, read the output, and know from our calibration constantswhat the resulting measurement is in physical units.

13.3.1 Calibration Procedure

Calibration of LSCT (Linear Strain Conversion Transducer)

The LSCT is calibrated using a known standard, the 0-1” micrometer head on a fixture that holds the LSCT”face to face” with the micrometer anvil. The micrometer can be moved by any desired increment (downto .001 inches if necessary) and the resulting output voltage is recorded at each point along the range overwhich calibration is desired. The range we will calibrate our instrument over is 0-1” and we will take a seriesof readings in .1” increments over the entire range. Additionally, we will take a smaller increment series ofreadings about the middle of our range, say, from .5 to .6” and take these readings at the .025” increments.Our complete set of input points will start at 0” and go: .1, .2, .3, .4, .5, .525, .550, .575, .6, .7, .8, .9, and1.000”, for a total of 14 readings. For each physical input change we will read and record the correspondingoutput voltage. When completed, a calibration plot and corresponding transducer formula can be generatedin MS Excel, or any similar software package. Using statistical analysis we will also analyze our transducerfor linearity.

1. Obtain LSCT transducer and record: Serial number, range, date of today’s calibration, and your groupcolor.

2. Obtain calibration fixture with the micrometer head. Take the time to examine the fixture such thatyou are familiar with its proper usage. If you are uncertain, ask your TA for assistance.

3. Insert the LSCT in the fixture and lock it down using the allen key. Make certain that the micrometerhead reads exactly 1.000 inches. When mounting the LSCT in the fixture, slide the plunger up to theface of the micrometer rod and ensure that it just barely physical touches.IT MUST TOUCH.

4. Plug the transducer into the 10 volt excitation receptacle as explained in classroom discussion.

5. Insert the voltmeter probes into the excitation jacks on the lab island panel. Record the excitationvoltage with the transducer plugged it. Then move the voltmeter probes to the transducer output jackson the panel.

6. Start your calibration and record each input parameter, its incremental change, the resulting outputvoltage reading (in millivolts, 1/1000 of a volt), and the incremental voltage change from the previousreading.

7. Record all 14 data points in the data sheet and use MS Excel to reduce your data as described in class.Remember to convert the units from inches to millimeters.

Calibration of Force transducer

The calibration of the force transducer is similar to the procedure outlined above for the LSCT. However,the physical quantity will be in kilogram force (kgf) and the calibration range of the force transducer will be



from 0 to 200 kgf, in 10 kgf increments. This makes a total of 21 points of input and 21 corresponding outputvoltage readings. The process is the same but dealing with the load frames used in this procedure (and safeusage) will explained in detail during class. Remember to transform the units from kgf to Newton (N).

13.4 Report

For the report, be sure to include:

• Memo to Mike Linger

• Plot with data on same page. Display equation of best fit line andR2 value taken to 5 decimal places.

• Include raw data


13. Instrumentation and Calibration 79

Calibration Data Sheet (LSCT)

Date Tested by

Transducer type Serial number

ExcitationVoltage

MicrometerReading

Incrementaldisplacement

Transduceroutput

Change intransduceroutput

(V) (in) (in) (mV) (mV)



Calibration Data Sheet (Force)

Date Tested by

Transducer type Serial number

ExcitationVoltage

Mass Added IncrementalApplied Force

Transduceroutput

Change inTransducerOutput

(V) (kg) (N) (mV) (mV)


Chapter 14

Shrink/Swell Properties of Expansive Soils

14.1 Purpose

This test method outlines procedures for demonstrating the shrink/swell potential of a given soil sample.Typically, the shrink/swell test is performed on soils with a high shrink/swell potential. These soils aregenerally clays that undergo large volume changes from cycles of wetting and drying. In this test, water willbe introduced to a sample that is laterally restrained with a constant load applied, and the one-dimensionalvolume change will be measured with respect to time. This test method is most commonly performed onundisturbed samples of fine grained soils naturally sedimented in water, although the same procedures canbe applied to compacted soils.

14.2 Apparatus

• Consolidometer - A device to hold the specimen in a ring that is either fixed to the base or floating(supported by friction on periphery of specimen) with porous disks on each face of the specimen.The inside diameter of the ring shall be determined to a tolerance of 0.075mm (0.003in). The Con-solidometer shall also provide a means of submerging the specimen, for transmitting the concentricvertical load to the porous disks, and for measuring the change in height of the specimen.

- Minimum Specimen Diameter - The minimum specimen diameter shall be 50mm (2.00in).

- Minimum Specimen Height-The minimum initial specimen height shall be 12mm (0.5in), butshall be not less than ten times the particle diameter.

- Minimum Specimen Diameter-to-Height Ratio-The minimum specimen Diameter-to-Height Ra-tio shall be 2.5

- Specimen Ring Rigidity-The rigidity of the ring shall be such that, under hydrostatic stress con-ditions in the specimen, the change in diameter of the ring will not exceed 0.03% of the diameterunder the greatest load applied.

- Specimen Ring Material-The ring shall be made of a material that is non-corrosive in relation tothe soil tested. The inner surface shall be highly polished or shall be coated with a low frictionmaterial. Silicone grease of molybdenum disulfide is recommended; polytetrafluoroethylene isrecommended for non-sandy soils.

• Porous Disks-The porous disks shall be of silicone carbide, aluminum oxide, or similar non-corrosivematerial. The grade of the disks shall be fine enough to prevent intrusion of soil into the pores. If nec-essary, a filter paper may be used to prevent infusion of soil into the disks; however, the permeability


of the disks, and filter paper, if used, must be at least one order of magnitude higher than that of thespecimen.

• Specimen Trimming Device-A trimming turntable or a cylindrical cutting ring may be used for trim-ming the sample down to the inside diameter of the consolidometer ring with a minimum of distur-bance. A cutter having the same inside diameter as the specimen ring shall attach to or be integral withthe specimen ring. The cutter shall have a sharp edge, a highly polished surface and be coated with alow-friction material. Alternatively, a turntable or trimming lathe may be used. The cutting tool mustbe properly aligned to form a specimen of the same diameter as that of the ring.

• Deformation Indicator-To measure change in specimen height, with a readability of 0.0025mm (0.0001in.).(Deformation transducer).

• Miscellaneous Equipment-Including timing device with a 1s readability, distilled or de-mineralizedwater, spatulas, knives, wire saws, used in preparing the specimen.

Environment-Tests shall be performed in an environment where temperature fluctuations are less than±4oC(±7oF) and there is no direct exposure to sunlight.

14.3 Specimen Preparation

All possible precautions should be taken to minimize disturbance of the soil or changes in moisture anddensity during specimen preparation. Avoid vibration, distortion, and compression.

1. Prepare test specimens in an environment where soil moisture change during preparation is minimized.A high humidity environment is usually used for this purpose.

2. Trim the specimen and insert it into the consolidation ring. When specimens come from undisturbedsoil collected using sample tubes, the inside diameter of the shall be at least 5mm (0.25in) greaterthan the inside diameter of the consolidation ring. It is recommended that either a trimming turntableor cylindrical cutting ring be used to cut the soil to the proper diameter. When using a trimmingturntable, make a complete perimeter cut, reducing the specimen diameter to the inside diameter ofthe consolidation ring. Carefully insert the specimen into the consolidation ring, by the width of thecut, with a minimum of force. Repeat until the specimen protrudes from the bottom the ring. Whenusing a cylindrical cutting, trim the soil to a gentle taper in front of the cutting edge. After the taperis formed, advance the cutter a small distance to form the final diameter. Repeat the process until thespecimen protrudes from the ring.

3. Trim the specimen flush with the plane ends of the ring. The specimen may be recessed slightly belowthe top of the ring, to facilitate centering of the top of the stone, by partial extrusion and trimmingof the bottom surface. For soft to medium soils, a wire saw should be used for trimming the top andthe bottom of the specimen to minimize smearing. A straightedge with a sharp cutting edge may beused for the final trim after the excess soil has first been removed with a wire saw. For stiff soils,a sharpened straightedge alone may be used for trimming the top and bottom. If a small particle isencountered in any surface being trimmed, it should be removed and the resulting void filled with soilfrom the trimmings.

4. Determine the initial wet mass of the specimen,MTo , in the consolidation ring by measuring the massof the ring with the specimen and subtracting the mass of the ring.


14. Shrink/Swell Test 83

5. Determine the initial height,Ho, of the specimen to the nearest 0.025mm (0.001in.) by taking theaverage of at least 4 evenly spaced measurements over the top and bottom surfaces of the specimenusing a dial comparator or other suitable measuring device.

6. Compute the initial volume,Vo, of the specimen to the nearest 0.25cm3 (0.015in3) from the diameterof the ring and the initial specimen height.

7. Obtain two or three natural water content determinations of the soil in accordance with Method D2216from material trimmed adjacent to the test specimen if sufficient material is available.

14.4 Procedures

1. Preparation of the porous disks and other apparatus will depend on the specimen being tested. Theconsolidometer must be assembled in such a manner as to prevent a change in water content of thespecimen. Dry porous disks and filters must be used with dry, highly expansive soils and may be usedfor all other soils. Damp disks may be used for partially saturated soils. Saturated disks may be usedwhen the specimen is saturated and known to have a low affinity for water. Assemble the ring withthe specimen, porous disks, filter disks (when needed) and consolidometer. If the specimen will notbe inundated shortly after application of the seating load, enclose the consolidometer in a lose fittingplastic or rubber membrane to prevent change in specimen volume due to evaporation.

2. After assembly of the consolidometer, secure a displacement transducer and/or dial gauge to the con-solidometer in a manner to prevent disturbance during the experiment. At time zero, add distilledwater to the consolidometer. Take readings at 0.25, 0.5, 1, 2, 4, 8, 15, 30, 60, 120, 240, 480, 960,1440, 2880, 5760 minutes, etc. Be sure to keep the sample submerged in water, and add distilled waterif necessary.

3. Once the test has been completed, obtain a final water content of the sample by weighing the ring withsample to determine the final weight, and oven dry the entire sample for a period of at least 12 hours.

14.5 Calculations

The goal of this test is to determine the shrink/swell potential of a soil sample. To do this, the followingparameters need to be determined.

14.5.1 Shrinkage Limit

To determine the shrinkage limit, first determine the mass of soil solids in the soil sample:

Ms =Mt

1 + winitial(14.1)

WhereMs is the mass of the soil solids in the sample;Mt is the initial total mass of the sample beforeswelling; andwinitial is the initial water content of the sample before swelling.

Then determine the dry density of the sample using:

ρdry =Ms

Vt(14.2)

Whereρdry is the dry density of the sample before swelling; andVt is the total volume of the samplebefore swelling.



The shrinkage limit of the soil is then calculated using:

SL =ρw

ρdry− 1

Gs(14.3)

WhereSL is the shrinkage limit of the sample in decimal form;ρw is the density of water;Gs is thespecific gravity of the soil solid particles (assume 2.7 unless otherwise specified)

Using time-deformation data, you can plot the percentage of swell of the sample as a function of time.The percentage swell is given by:

S =∆L

L0∗ 100% (14.4)

WhereS is swell in percent (%);DL is the change in height of the sample;L0 is the initial sampleheight.

Lastly, you can compare the experimentally measured and the theoretically calculated volume change.The theoretical volume change can be calculated as:

∆L

L0= ∆w ∗

ρdry

ρw∗ 100% (14.5)

WhereDw is the increase in water content from the shrinkage limit in decimal form given by:

∆w = wfinal − SL (14.6)

Wherewfinal is the final water content of the sample.

14.6 Report


• Final displacement reading

• Shrinkage Limit

• Percentage swell versus time(min) plot

• Theoretical volume change

• Actual volume change

• Initial and final degrees of saturation

• Initial and final water contents


14. Shrink/Swell Test 85

Swell Test Data Sheet

Date Tested bySection No. Group No.Description of sample

Mass of sample ring Mass of sample ring + 1Diameter of sample ring Height of sample ring

Laterally Constrained Test

Initial sample height Initial sample massInitial sample volume Final sample height

Test Before AfterContainer No.Mass of container (g)Mass of wet soil + container (g)Mass of dry soil + container (g)Mass of dry soil (g)Mass of water (g)Water content, (%)



Time Deformation Data Sheet

Elapsed time Displacement reading Net displacement(mm) (in)


Chapter 15

One-Dimensional Consolidation

15.1 Purpose

A surface load, for example due to the construction of a building, results in increased stresses in the under-lying soils. The increase in stress also causes settlements. When the soils are fine grained and saturated theincrease in total stress is carried by the water, as excess pore pressure. Since these soils have low hydraulicconductivity the excess pore pressure will dissipate slowly and the settlement will be delayed in time.

The consolidation test, or oedometer test, is used to determine the parameters that can be used to estimateboth the magnitude and the time rate of the settlements. The test is performed on a cylindrical specimen,constrained laterally by a ring and allowed to compress under a constant load. The load is held on thesample for 24 hours or until all excess pore pressure is dissipated. During this time the change in height ismeasured. The load is usually doubled at the end of the 24 hour period and the process repeated. Usually 5or 6 load increments are applied and then data are taken during one unloading step. The measurements areused to determine the relationship between the effective stress and void ratio or strain, and the rate at whichconsolidation can occur.

This test method uses conventional consolidation theory based on Terzaghi’s consolidation equation tocompute the coefficient of consolidation,cv. The analysis is based on the following assumptions:

• The soil is saturated and has homogeneous properties.

• The flow of pore water is in the vertical direction.

• The compressibility of soil particles and pore water is negligible compared to the compressibility ofthe soil skeleton.

• The stress-strain relationship is linear over the load increment.

• The ratio of soil permeability to soil compressibility is constant over the load increment.

• Darcy’s law for flow through porous media applies.


ASTM D 2435 - Standard test method for one-dimensional consolidation properties of soils.



• Load Device - A suitable device for applying vertical loads or total stresses) to the specimen. Thedevice should be capable of maintaining specified loads for long periods of time with an accuracy of± 0.5% of the applied load and should permit quick application of a given load increment withoutsignificant impact.

• Consolidometer - A device to hold the specimen in a ring that is either fixed to the base or floating(supported by friction on periphery of specimen) with porous disks on each face of the specimen. Theinside diameter of the ring shall be determined to a tolerance of 0.075mm (0.003in). The consolidome-ter shall also provide a means of submerging the specimen, for transmitting the concentric vertical loadto the porous disks, and for measuring the change in height of specimen.

- The minimum specimen diameter is 50 mm (2.00 in).

- The minimum specimen height is 12 mm (0.5 in), but not less than ten times the maximumparticle diameter.

- The minimum specimen diameter-to-height ratio is 2.5.

- The ring must be made of a material that is noncorrosive in relation to the soil tested. The innersurface needs to be highly polished or coated with a low-friction material.

• Porous disks - The porous disks are made of noncorrosive material. The grade of the disks shall befine enough to prevent intrusion of soil into the pores. If necessary, filter paper may be used to preventintrusion of the soil into the disks; however, the permeability of the disks, and filter paper, if used,must be at least one order of magnitude higher than that of the specimen.

• Specimen trimming device - A trimming turntable or a cylindrical cutting ring may be used for trim-ming the sample down to the inside diameter of the consolidometer ringwith a minimum of distur-bance. The specimen ring has a sharp edge that can be used as a cutter. Alternatively, a turntable ortrimming lathe may be used. The cutting tool must be properly aligned to form a specimen of the samediameter as that of the ring.

• Deformation indicator - To measure change in specimen height, with a readability of 0.0025 mm(0.0001 in.).

• Miscellaneous equipment - A timing device with 1 s readability, distilled or demineralized water,spatulas, knives, and wire saws, used in preparing the specimen.

Tests shall be performed in an environment where temperature fluctuations are less than±4oC(±7oF )and there is no direct exposure to sunlight.

15.3 Specimen Preparation

All possible precautions should be taken to minimize disturbance of the soil or changes in moisture anddensity during specimen preparation. Avoid vibration, distortion, and compression.

1. Prepare test specimens in an environment where soil moisture change during preparation is minimized.A high humidity environment is usually used for this purpose.


15. One-Dimensional Consolidation 89

2. Trim the specimen and insert it into the consolidation ring. When using a cylindrical cutting ring, trimthe soil to a gentle taper in front of the cutting edge. After the taper is formed, advance the cutter asmall distance to form the final diameter. Repeat the process until the specimen protrudes from thering.

3. Trim the specimen flush with the plane ends of the ring. For soft to medium soils, a wire saw shouldbe used for trimming the top and bottom of the specimen to minimize smearing. A straightedge witha sharp cutting edge may be used for the final trim after the excess soil has first been removed with awire saw. For stiff soils, a sharpened straightedge alone may be used for trimming the top and bottom.If a small particle is encountered in any surface being trimmed, it should be removed and the resultingvoid filled with soil from the trimmings.

4. Determine the initial wet mass of the specimen,MTo, in the consolidation ring by measuring the massof the ring with specimen and subtracting the tare mass of the ring.

5. Determine the initial height,Ho, of the specimen to the nearest 0.025 mm (0.001 in.) by taking theaverage of at leastfour evenly spaced measurements over the top and bottom surfaces of the specimenusing a dial comparator or other suitable measuring device.

6. Compute the initial volume,VO, of the specimen to the nearest0.25cm3(0.015in3) from the diameterof the ring and the initial specimen height.

7. Obtain two or three natural water content determinations of the soil from material trimmed adjacent tothe test specimen if sufficient material is available.

15.4 Procedure

1. Preparation of the porous disks and other apparatus will depend on the specimen being tested. Theconsolidometer must be assembled in such a manner as to prevent a change in water content of thespecimen. Dry porous disks and filters must be used with dry, highly expansive soils and may be usedfor all other soils. Damp disks may be used for partially saturated soils. Saturated disks may be usedwhen the specimen is saturated and known to have a low affinity for water. Assemble the ring withspecimen, porous disks, filter disks (when needed) and consolidometer. If the specimen will not beinundated shortly after application of the seating load, enclose the consolidometer in a loose fittingplastic or rubber membrane to prevent change in specimen volume due to evaporation.

2. Place the consolidometer in the loading device and apply a seating pressure of 5 kPa (100lbf/ft2).Immediately after application of the seating load, adjust the deformation indicator and record the initialzero reading,do. If necessary, add additional load to keep the specimen from swelling. Conversely, ifit is anticipated that a load of5kPa(100lbf/ft2) will cause significant consolidation of the specimen,reduce the seating pressure to 2 or 3 kPa (about 50lbf/ft2) or less.

3. If the test is performed on an intact specimen that was either saturated under field conditions or ob-tained below the water table, inundate shortly after application of the seating load. As inundation andspecimen wetting occur, increase the load as required to prevent swelling. Record the load required toprevent swelling and the resulting deformation reading.

4. The specimen is to be subjected to increments of constant total stress.



5. The standard loading schedule shall consist of a load increment ratio (LIR) of one which is obtainedby doubling the pressure on the soil to obtain values of approximately 12, 25, 50, 100, 200, etc. kPa(250, 500, 1000, 2000, 4000, etc.lbf/ft2).

6. The standard rebound or unloading schedule should be selected by halving the pressure on the soil(that is, use the same increments as before, but in reverse order). However, if desired, each successiveload can be only one-fourth as large as the preceding load, that is, skip a decrement. An alternativeloading, unloading, or reloading schedule may be employed that reproduces the construction stresschanges or obtains better definition of some part of the stress deformation (compression) curve, oraids in interpreting the field behavior of the soil.

7. Before each pressure increment is applied, record the height or change in height,df , of the specimen.

8. The standard load increment duration is 24 h. Record the height or change in height,d, at timeintervals of approximately 0.1, 0.25, 0.5, 1, 2, 4, 8, 15 and 30 min, and 1, 2, 4, 8 and 24 h. Takesufficient readings near the end of the pressure increment period to verify that primary consolidationis completed. For some soils, a period of more than 24 h may be required to reach the end-of-primaryconsolidation.

9. To minimize swell during disassembly, rebound the specimen back to the seating load (5 kPa). Onceheight changes have ceased (usually overnight), dismantle quickly after releasing the final small loadon the specimen. Remove the specimen and the ring from the consolidometer and wipe any free waterfrom the ring and specimen. Determine the mass of the specimen in the ring and subtract the taremass of the ring to obtain the final wet specimen mass,MTf . The most accurate determination of thespecimen dry mass and water content is found by drying the entire specimen at the end of the test. Ifthe soil sample is homogeneous and sufficient trimmings are available for the specified index testing,then determine the final water content,wf , and dry mass of solids,Md, using the entire specimen.

15.5 Calculation

The goal of this test is to determine the magnitude of settlement and the rate of settlement. For this purpose,the compression index,Cc, the re-compression index or swelling index,Cr, the coefficient of secondarycompression,Cα, the coefficient of consolidation,cv, and the pre-consolidation pressureσzc must be ob-tained from the data. Consult your textbook for the appropriate methods to use for interpretation of thedata.

15.6 Report


• cv, Cα, and void ratio for each day

• Void ratio versus effective stress plot

• σ′zc, Cc, Cr

• Displacement versus time for each day included in appendix


15. One-Dimensional Consolidation 91

Consolidation Data

Sample No. Project

Boring No. Location

Depth


Date Tested by

Load(kPa)

12 25 50 100 200 25 Seat

Time Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7


Chapter 16

Plaxis exercise 2: consolidation settlementscalculation

The third phase of the project requires you to evaluate the settlements of the embankment due to consolida-tion of the soft marine clay. During this exercise we are going to simulate the construction of the embankmentin three steps. After each step we will let the soil consolidate for a time before applying a new load incre-ment. The delay is required to allow the soil to gain strength. If the embankment were built in one step thesoil wouls fail.

16.1 Consolidation settlements of an embankment during construction andafter completion

16.1.1 Input of geometry

Start Plaxis 7.2 Professional, Plaxis Input and select your old project, developed in the first Plaxis exercise.If the title of the project does not appear on the list, select “More files” and navigate to the folder where theproject is located.

The geometry input needs to be changed because we are going to simulate the construction of the em-bankment in three steps. We need to draw the geometry lines that define the three layers that will be placed.The boundaries of the foundation soil (the marine clay) will also need to be extended.

- Select theGeometry linetool on the top left of the toolbar.

- Draw a line from point (16.0, 10.5) to point (46.0, 10.5) defining the first layer. Notice that points arecreated at the intersection between the new line and the lines delimiting the core. Right click to exitthe drawing tool.

- Draw the line between the second and the third layer between point (22.0, 12.5) and point (40.0, 12.5).

- Click on and drag point “0” to the left as much as possible. Hold the shift key to ensure the bottomline remains horizontal.

- Repeat with point “3”, so that point “0” and “3” are aligned.

- Repeat on the right boundary.


Figure 16.1: Geometry input of the embankment.

Plaxis parameter= Description Valueλ∗ = 0.434Cc

1+eoVirgin compression

κ∗ = 0.434Cr1+eo

Unload-reloadk =Cvmvγw Hydraulic conductivity and time ratec’ = c’ Cohesion 5kPaφ′ = φ′ Friction angle 30 degreesΨ = Ψ Dilatancy 0

Table 16.1: Relationships between clay properties and Plaxis parameters.

16.1.2 Input of material parameters

In this part you assign the new material parameters that describe the response of the soil. We have two soilsin this problem: a soft marine clay as a foundation, and a clayey sand for the compacted soil embankment.At this point we will disregard the drain material. In the first Plaxis exercise the only important materialparameter was the hydraulic conductivity. In this exercise selecting the correct mechanical properties of thematerials involved is essential for predicting the settlements. Plaxis offers five possible material models torepresent the response of soils. The linear elastic material model is not effective when trying to representconsolidation problems, therefore a different model must be selected. In our experience, the soft soil modelgives quite realistic predictions of the actual response of soft clays, such as the one at our site. This modelis quite complicated mathematically and requires a total of seven parameters to describe the stress-strainresponse and the failure conditions.

The data from a consolidation test on a sample of the soft marine clay, such as those you have been test-ing, are given in figures16.2. You can determineCc andCr from this figure. The coefficient of consolidationCv was determined to be 6.37×10−2m2/day. The value of the modulus od volumetric compressibility (mv)is calculated from the consolidation curve plotted in the strain vs. vertical effective stress space. You canfind the curve and a plot of the variation ofmv in figure16.3.

Complete table16.1with the Plaxis parameters you derive from the results of the consolidation test.The embankment material will be modeled as a linear elastic-perfectly plastic material with parameters

in table16.2.Follow these steps to change the material data sets:

- Click on theMaterial setsbutton on the toolbar.

- Double click on the “clay” to edit the soft marine clay material data set.


16. Plaxis exercise 2: consolidation settlements calculation 95

Figure 16.2: Consolidation curve for the marine clay.

Plaxis parameter= Value DescriptionE =2.0×104 kPa Young modulusν = 0.20 Poisson ratioc’ = 1 kPa Cohesionφ′ = 35 degrees Friction angleΨ = 0 Dilatancy

Table 16.2: Material parameters for the embankment material.



Figure 16.3: Consolidation curve in strain vs. vertical effective stress and modulus of volume compressibilityfor the marine clay.



- SelectSoft soil modelfor Material model.

- SelectUndrainedfor Material type.

- Enter the parameters from table16.1, including those you calculated.

- Click “OK” and “Apply”.

- Double click on the “clayey sand” to edit the embankment material data set.

- SelectMohr Coulombfor Material model.

- SelectDrained for Material type.

- Enter the parameters from table16.2.

- Click “OK” and “Apply”.

16.1.3 Generation of new mesh

Since new geometry lines were added, a new mesh must be generated.

- In the mesh menu select “Global coarseness” and then “Medium”.

- Click on “Generate mesh” on the right of the toolbar

- Click on update when the new window appears.

16.1.4 Initial conditions

Once the geometry is defined, the materials selected and the discretization completed, you need to input theinitial conditions. In this case you will need to define both the initial pore pressures and the initial stresses.Click on the green arrow on the top right of the toolbar to go to theInitial conditionssection.

Generation of pore pressures

The geometry should look all gray. If not, you need to make sure the “green light” on the left is selected.

- Select thePhreatic linetool on the top left of the toolbar.

- Draw the groundwater level at the ground surface, or 8.5 m. Click on the left boundary at height 8.5m and then click on the right boundary at 8.5 m. Right click to end the line.

- Click onGenerate water pressures, the button with blue crosses.

- Select:Phreatic lineand “OK”.

- A new window appears with the calculated initial pore pressures. It is easier to interpret the results byselectingshadingsfrom the drop down menu. Do the results agree with what you expected?

- Click onUpdate.

Generation of initial stresses

Select the other green light button in the middle of the toolbar. The geometry should now appear in color.The initial stresses are calculated before construction begins, therefore we need to de-select the embankment.As you click on the clusters (areas) forming the embankment they should become white like the background.This tells the program to ignore the weight of those areas in the calculations. Click onGenerate initialstresses, the button with the red crosses, to calculate. The pop up window shows the values ofKo that willbe used in the calculations and OCR (or POP=pre-consolidation pressure). Click OK to accept the proposedvalues. Check that the calculated stresses are what you would expect them to be, and update.



Figure 16.4: Mesh of the embankment.



16.2 Calculations

Click on the green arrowCalculateto go to the calculations section of Plaxis. In this part we will define allthe phases of construction and the periods of consolidation. First, define all phases of the problem.

- Click next to create a new phase. We need to “build” the first layer of the embankment.

- OnCalculation typeselectPlasticandLoad adv. ultimate level.

- On theParameters tabselect Staged construction (on the bottom right section) and click onDefine.

- The geometry appears, click on the areas forming the first layer of the embankment. They shouldbecome colored as you click on them. Now the program is going to add the weight of the first layer.

- Click next to create a new phase. We need to allow consolidation to occur.

- OnCalculation typeselectConsolidationandAutomatic time stepping.

- On theParameters tabselectUltimate time intervaland input the length of time before the next layerof the embankment is placed. For example 120 days.

- Repeat the same procedure for the next two layers. For the second consolidation phase use 180 days.If you forget and use 120 days the embankment will fail when the third layer of soil is added.

- On the last consolidation phase, selectMinimum pore pressureto allow consolidation to continue untilthe excess pore pressures are dissipated.

Once all the calculation phases are defined, you need to select some special points for which you wouldlike to plot stress-strain curves, settlement vs. time curves, etc... Click on theSelect points for curvesbutton,the one with red and white crosses in the toolbar. A new window appears with all the points tacked by thefinite element calculations. Enlarge the central portion of the embankment and select a point on the originalground surface in the center of the embankment. Other points of interest are at the center of the clay layerand at the toe of the embankment. The displacements are calculated at these points. To get the stress points,click on the buttonSelect stress points for stress/strain curves, the red triangle with crossesinside. Thenselect points in the mesh that are close to the points you selected earlier. notice that the point are not thesame, but possible you can get close. If you make a mistake you cannot undo, but it’s not a problem: you’llhave more info than you need.

Now you are ready to calculate the problem. Check that each phase is preceded by a blue arrow. Ablue arrow means that the program will actually perform the calculations related to this phase. Click on thegreen arrowCalculateon the toolbar. The calculation starts. This may take a while. In the window thatpops up you want to look at the value ofΣ −Mstage for the “plastic” phases, as well as the Global error.Σ−Mstage increasing shows the percentage of weight being applied, from 0 to 1. During the consolidationphases, look at the Time increase and Pmax, the maximum pore pressure, decrease. Once the calculation iscompleted the blue arrow will become a green cross.

Select the phase you want to see and click on the green arrowOutput. Do not double click, you willdeselect the phase. The usual output window will appear. Explore the results for each phase. Look at totaldisplacements (since the beginning) or total increments (during this phase only). Use the different views:arrows, shadings, or contours. Also look at the excess pore pressures in the different views. You can drawcross sections with thecross section(A-A’) button. Clicking on the Table button will give you the actualvalues for each point in the figure you are seeing.


Chapter 17

Direct Shear Test of Soils UnderConsolidated Drained Conditions

”The following method departs from the ASTM Standard D3080, copyrightc©American Society for Testingand Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959”

17.1 Purpose

This test method covers the determination of the consolidated drained shear strength of a soil material indirect shear. The test is performed by deforming a specimen at a controlled strain rate on or near a singleshear plane determined by the configuration of the apparatus. Generally, three or more specimens are tested,each under a different normal load, to determine the effects upon shear resistance and displacement, andstrength properties such as Mohr strength envelopes. Shear stresses and displacements are nonuniformlydistributed within the specimen. An appropriate height cannot be defined for calculation of shear strains.Therefore, stress-strain relationships or any associated quantity such as modulus, cannot be determined fromthis test.

17.2 Terminology

• Relative Lateral Displacement-The horizontal displacement of the top and bottom shear box halves.

• Failure-The stress condition at failure for a test specimen. Failure is often taken to correspond to themaximum shear stress attained, or the shear stress at 15 to 20 percent relative lateral displacement.Depending on soil behavior and field application, other suitable criteria may be defined.

17.3 Apparatus

• Shear Device-A device to hold the specimen securely between two porous inserts in such a way thattorque is not applied to the specimen. The shear device shall provide a means of applying a normalstress to the faces of the specimen, for measuring change in thickness of the specimen, for permittingdrainage of water through the porous inserts at the top and bottom boundaries of the specimen, andfor submerging the specimen in water. The device shall be capable of applying a shear force to thespecimen in water. The device shall be capable of applying a shear force to the specimen along apredetermined shear plane (single shear) parallel to the faces of the specimen. The frames that holdthe specimen shall be sufficiently rigid to prevent their distortion during shearing. The various parts


of the shear device shall be made of material not subject to corrosion by moisture or substances withinthe soil, for example, stainless steel, bronze, or aluminum, etc. Dissimilar metals, which may causegalvanic action, are not permitted.

• Shear Box, a shear box, either circular or square, made of stainless steel, bronze, or aluminum, withprovisions for drainage through the top and bottom. The box is divided vertically by a horizontal planeinto two halves of equal thickness which are fitted together with alignment screws. The shear box isalso fitted with gap screws, which control the space (gap) between the top and bottom halves of theshear box.

• Porous Inserts, Porous inserts function to allow drainage from the soil specimen along the top andbottom boundaries. They also function to transfer horizontal shear stress from the insert to the top andbottom boundaries of the specimen. Porous inserts shall consist of silicon carbide, aluminum oxide, ormetal which is not subject to corrosion by soil substances or soil moisture. The proper grade of insertdepends on the soil being tested. The permeability of the insert should be substantially greater thanthat of the soil, but should be textured fine enough to prevent excessive intrusion of the soil into thepores of the insert. The diameter or width of the top porous insert or plate shall be 0.01 to 0.02 in. (0.2to 0.5 mm) less than that of the inside of the ring. If the insert functions to transfer the horizontal stressto the soil, it must be sufficiently coarse to develop interlock. Sandblasting or tooling the insert mayhelp, but the surface of the insert should not be so irregular as to cause substantial stress concentrationsin the soil.

• Device for Applying and Measuring the Normal Force-The normal force is applied by a lever loadingyoke which is activated by dead weights (masses) or by a pneumatic loading device. The device shallbe capable of maintaining the normal force to within 61 percent of the specified force quickly withoutexceeding it.

• Device for Shearing the Specimen-The device shall be capable of shearing the specimen at a uniformrate of displacement, with less than 65 percent deviation, and should permit adjustment of the rateof displacement from 0.0001 to 0.04 in./min (.0025 to 1.0 mm/min). The rate to be applied dependsupon the consolidation characteristics of the soils (see 9.12.1). The rate is usually maintained with anelectric motor and gear box arrangement and the shear force is determined by a load indicating devicesuch as a proving ring or load cell. 6.4.3 The weight of the top shear box should be less than 1 percentof the applied normal force: this may require that the top shear box be modified and supported bycounter force.

• Shear Force Measurement Device-A proving ring or load cell accurate to 0.5 lbf (2.5 N), or 1 percentof the shear force at failure, whichever is greater.

• Shear Box Bowl-A metallic box which supports the shear box and provides either a reaction againstwhich one half of the shear box is restrained, or a solid base with provisions for aligning one half ofthe shear box, which is free to move coincident with applied shear force in a horizontal plane.

• Miscellaneous Equipment, including timing device with a second hand, distilled or demineralizedwater, spatulas, knives, straightedge, wire saws, etc., used in preparing the specimen.

17.4 Procedure

1. Assemble the shear box.


17. Direct Shear Test of Soils Under Consolidated Drained Conditions 103

2. Place moist porous inserts over the exposed ends of the specimen in the shear box; place the shear boxcontaining the undisturbed specimen and porous inserts into the shear box bowl and attach the shearbox.

3. Connect and adjust the shear force loading system so that no force is imposed on the load measuringdevice.

4. Properly position and adjust the horizontal displacement measurement device used to measure sheardisplacement. Obtain an initial reading or set the measurement device to indicate zero displacement.

5. Place a moist porous insert and load transfer plate on the top of the specimen in the shear box.

6. Place the normal force loading yoke into position and adjust it so the loading bar is horizontal.

7. Apply a small normal load to the specimen. Verify that all components of the loading system are seatedand aligned. The top porous insert and load transfer plate must be aligned so that the movement of theload transfer plate into the shear box is not inhibited. Record the applied vertical load and horizontalload on the system.

8. Attach and adjust the vertical displacement measurement device. Obtain initial reading for the verticalmeasurement device and a reading for the horizontal displacement measurement device.

9. Select the appropriate displacement rate.

10. Shear the specimen, until the shear resistance measured by the load transducer levels off indicatingthat the specimen has failed.

17.5 Calculation

Calculate the nominal shear stress:

τ =F

A

where:

• τ = nominal shear stress (lbf/in2,kPa),

• F = shear force (lbf, N),

• A = initial area of specimen (in2, mm2).

Calculate the normal stress acting on the specimen:

n =N

A

where:

• n = normal stress (lbf/in2, kPa),

• N = normal vertical force acting on the specimen (lbf, N),

• A = initial area of specimen (in2, mm2).



17.6 Report


• Shear stress versus time for each normal stress

• Mohr Circle plot withφ, τ versus n


17. Direct Shear Test of Soils Under Consolidated Drained Conditions 105

Shear Test Data

Initial Reading Initial Reading Initial Reading

Load Applied Load Applied Load Applied

Seconds Reading Seconds Reading Seconds Reading(mV) (mV) (mV)


Chapter 18

Triaxial Unconfined Compression Test

18.1 Purpose

This test will be used to quickly determine the undrained shear strength of saturated clays. In this test, noradial stress will be applied to the sample (σ3=0), but the axial stress, (σ1) will be increased until the samplefails (can no longer support load). The load is applied quickly so that the pore water cannot drain, meaningthat the sample is sheared at a constant volume. Since we are not applying a radial stress, the principle ofeffective stresses gives:

σ′3 = σ3 −∆u = 0−∆u = −∆u (18.1)

Because soils cannot sustain tension,σ3 must be positive, and therefore, the excess water stresses,∆u,must be negative. The results from the UC test are used to:

• Estimate the short-term bearing capacity of fine-grained soils for foundations

• Estimate the short-term stability of slopes

• Compare the shear strengths of soils from a site to establish soil strength variability quickly and cost-effectively (the UC test is cheaper than others)

• Determine the stress-strain characteristics under fast (undrained) loading conditions

18.2 Procedure

18.2.1 Materials

• Soil sample

• Sample form and sample manual rammer for compaction

• Sample extruder

• Knife

• Sample holder

• Calipers

• Pressure chamber


• Porous stones

• Transducers - force and displacement

• Shearing apparatus

• Computer - Geotech Data Logger Program

• Digital Voltmeter

18.2.2 Procedure

1. Refer to Chapter 3, Compaction Using Standard Effort, for sample preparation.

2. The sample extruded may now be cut in two, lengthwise. Each group should take half of the originalsample.

3. Place the sample in the sample holder.

4. Each side of the sample holder cuts the sample to different diameters; one for a coarse preparation,and one for a final sample preparation

5. Carefully, (very carefully), shave the sample with the knife so that the final product is a cylindricalsample with a diameter equal to that of the sample holder.

6. Take the sample and lay it horizontally on the sample holder. Using the edge of the holder, cut the endsoff of the sample so that they are square. You want a sample with a height-to-diameter ratio between2 and 2.5

7. Record the dimensions of the sample in several places and record the average height and diameter.

8. Disassemble the compression chamber

9. Place a porous stone on the bottom platen of the compression chamber. Then place the sample with aporous stone on top of it. Re-assemble the compression chamber, taking care to prevent the plungerfrom interfering with the sample.

10. Place the compression chamber with the sample inside it onto the loading frame.

11. Prepare the computer data acquisition system as directed.

12. Record the serial numbers of the force and displacement transducers

13. Begin data acquisition and then start applying a load to produce an axial strain at a rate of 1/2 to2%/min. Allow the computer to take the readings, and stop the data acquisition when the failure planein the sample is visible.

14. Save the computer data, and make a sketch of the failed sample, noting the angles of the failure planes.

15. Record a water content of the sample after completion of the test.


18. Triaxial Unconfined Compression Test 109

18.3 Calculations

The undrained shear strength is given as:

Su =Pz

2A=

12σ1 (18.2)

wherePz is the axial load applied to the sample and

A =Ao

(1− e1)(18.3)

Note that because we are assuming no volume change, and we are axially deforming our sample, thecross sectional area of the sample changes as the strain increases.

18.4 Report


• Force vs. time plot

• Displacement vs. time plot

• Stress versus strain plot

• σ versusτ plot, (including the Mohr’s circle)

• Values forsu andqu (ultimate stress, ors1 at failure)



Unconfined Compression Test Data

Sample No. Project

Boring No. Location

Depth


Date Tested by

Time Force Displacement(s) (mV) (mV)


Chapter 19

Unconsolidated Undrained Triaxial Test

19.1 Specimen preparation

The test will be carried out on a compacted specimen of clayey sand. Prepare the compacted specimenfollowing the directions on chapter7 and as directed by your teaching assistant. The procedure is similar tothat used for the preparation of the unconfined compression specimen. Once the soil is extruded, carefullydivide the sample into two parts and obtain one specimen from each part.

19.1.1 Preparation of the specimen

1. Trim the specimen to the desired dimensions: diameter 38mm (1.5in) and height 76mm (3in), usinga trimming device. The trimming apparatus should allow for convenient trimming of a cylindricalspecimen of constant cross section, using either a wire saw or a steel blade. Be careful during thetrimming and while handling the specimen because the material is prone to cracking and crumbling.The specimen should be slightly taller than the final desired height to allow the removal of top andbottom slices prior to final measurement and testing. Be particularly careful in trimming the specimenends to ensure they are perpendicular to the longitudinal axis of the specimen (otherwise alignmentbecomes a real problem).

2. Place the specimen on a small piece of saran wrap while you are handling it to avoid loss of moisture.

3. Obtain the moist weight of the specimen.

4. Measure height to 0.1mm (0.01in) with a caliper. Care should be taken that the measuring does notpenetrate soft specimens. The average of 3 readings should be used.

5. Measure the specimen diameter to 0.01mm (0.001in) in two perpendicular directions and three eleva-tions (center, near top and near bottom) to obtain an average.

6. Measure the thickness of the membrane. Usually this is done by folding the membrane and measuringthe thickness of several layers at a time and then dividing by the number of layers.

19.1.2 Fitting end caps and membrane

1. Carefully place the specimen on the bottom cap and then the top cap on the specimen. If needed,also place porous stones. Make sure the specimen is centered and the assembly is aligned (VERYIMPORTANT!!).


Figure 19.1: Stages of membrane fitting (from Head, 1992)

2. Fit two o-rings over the membrane stretcher and roll them near the middle of its length. Fit a membraneinside the stretcher and fold back the ends, over and outside. Apply vacuum to the membrane stretcher.Make sure the membrane is actually being pulled out and adheres to the stretcher. It may take a littletugging, but be careful not to twist the membrane at this point.

3. Carefully lower the membrane stretcher over the specimen until it is nicely centered. Then releasevacuum and allow the membrane to adhere to the specimen.

4. Carefully release the membrane ends covering the caps and trying to minimize the amount of airentrapped in contact with the sample.

5. Lower the stretcher so that the bottom is located at about mid-height of the lower cap. Roll down andoff one o-ring to seal the membrane.

6. Raise the membrane stretcher all the way up so that the bottom is located at about mid-height of thetop cap. Roll down and off the o-ring.

7. Carefully fold the membrane over the o-rings.

19.2 Procedure

1. Assemble the triaxial cell.

2. Carefully check that the piston is aligned with the top cap.

3. If not, undo the cell set up and try to gently adjust the alignment until it works. It is important that youdo so very gently as to minimize the disturbance to the sample.

4. Place the cell in the loading frame.


19. Unconsolidated Undrained Triaxial Test 113

5. Prepare the computer data acquisition system as directed.

6. Record the serial numbers of the transducers.

7. Slowly increase pressure in the cell to the desired confining pressure. Be careful, the loading rod maybe lifted by the pressure if it is not locked. Allow 10 minutes under confining pressure for the sampleto equilibrate.

8. Begin data acquisition and note the reading for the load transducer (this should be the “zero” reading,or no load is applied). Then start loading at a strain rate of approximately 1%/min. Before the loadingrod comes into contact with the top cap the load transducer is reading the upward force due to thechamber pressure and the friction between the rod and the seal.

9. Allow the computer to take the readings, and stop the data acquisition when the axial strains reach15%.

10. Save the computer data, and make a sketch of the failed sample, noting the angles of the failure planes.

11. Record a water content of the sample after completion of the test.

19.3 Calculations

The deviator stress is given as:

σ1 − σ3 =Pz

A(19.1)

wherePz is the axial load applied to the sample (corrected for uplift and friction and:

A =Ao

(1− e1)(19.2)

Note that because we are assuming no volume change, and we are axially deforming our sample, thecross sectional area of the sample changes as the strain increases.

You also need to correct the deviator stressσ1 − σ3 for the effect of the membrane:

∆(σ1 − σ3) =4Emtmε1

D(19.3)

where:Em is Young’s modulus of the membrane, use 1400 kPa;tm is the thickness of the membraneandε1 = ∆H/H is the vertical strain.

19.4 Report

Include the following information in the report:

• Rate of strain, in percent per minute.

• The stress-strain curve,(σ1 − σ3) vs. ε1.

• Axial strain at failure, in percent.

• The value of compressive strength and the major and minor principal stresses at failure.



• The sample water content

• A failure sketch of the specimen.


Appendix A

CVEN 365 Laboratory Design Project

A.1 Introduction

The CVEN 365 laboratory assignments are sequenced as a series of steps in the design of a retention pondfor storing treated effluent from a wastewater treatment plant. The tentative laboratory schedule is given inthe course syllabus and it is also reported in tableA.1.

The overall project is subdivided into four design tasks associated with individual laboratory sessions asindicated in tableA.2.

A.2 Report Submissions

Reporting is required at two levels: (1) data laboratory reports documenting the laboratory sessions, and(2) design reports in which soil parameters derived from laboratory measurements are applied to the designof the retention pond. All reports are individual and must be submitted at the beginning of the laboratorysession. Collaboration is encouraged during the collection and reduction of the data. However, each studentshall work on the evaluation of the results on her/his own and submit an original report.

A.2.1 Data laboratory reports

One week after each laboratory session a laboratory report shall be submitted containing the following in-formation:

• Name, date, laboratory section, laboratory test(s) performed. Descriptions of test procedures are notrequired. The report should simply make a concise statement as to the test performed with appropriatereference to the test procedure.

• Data measurements. Copies of handwritten records of measurements are required in the submission. Insome laboratory exercises, it may be convenient to tabulate and reduce data in a computer spreadsheetformat. Computer spreadsheets are acceptable, but are not a substitute for original records of datameasurements. All data sheets shall be initialed and dated by the person taking the measurement.

• Data reduction. Data measurements must generally be reduced to compute specific soil material pa-rameters. Data reduction in a computer spreadsheet format is acceptable. However, example hand-written calculations should be included in sufficient detail to allow a reviewer to track through all stepsof the data reduction.


Date Laboratory Subject AssignmentJan. 15-19 1 No laboratoryJan. 22-26 2 Particle size determination

Water contentJan. 29- Feb. 2 3 Determination of Atterberg limits Data report 1

Visual classificationFeb. 5-9 4 Proctor compaction test Data report 2

Total suction by filter paper methodFeb. 12-16 5 Determination of hydraulic conductivity Design Report 1

Flow nets drawingFeb. 19-23 6 Computer exercise 1: 2-D seepage Data report 3

Feb. 26-Mar. 2 7 Mohr circles Design Report 2Instrumentation

Mar. 5-9 8 Shrink test Data report 4Mar. 19-23 9 Consolidation Data report 5Mar. 26-30 10 Computer exercise 2: consolidation Data report 6 (draft)Apr. 2-6 11 Direct shear test Data report 6Apr. 9-13 12 Triaxial test: unconfined Design Report 3

Apr. 16-20, 2005 13 Triaxial test: unconsolidated undrained Data report 7Apr. 23-27, 2005 14 Computer exercise 3: strength Data report 8

Table A.1: Assignment schedule

Design Task Laboratory Sessions TopicI 2, 3, 4 Preliminary evaluation of soilsII 5, 6 Permeability and seepageIII 9, 10 Consolidation and settlementIV 11, 12, 13, (14) Strength and slope stability

Table A.2: Design tasks


A. CVEN 365 Laboratory Design Project 117

• Test evaluation. The report should conclude with (1) recommended soil material parameters (i.e.,liquid limit, unit weight, etc.) to be used in the project design, and (2) an assessment of the overalllevel of reliability of the reported material parameters and the reasons for such assessment.

Specific information to be included in the weekly reports will vary according to the specific tasks per-formed. Students should clarify any uncertainties in reporting requirements with the teaching assistant priorto leaving the laboratory session.

A.2.2 Design reports

Material parameters obtained from the laboratory sessions will be utilized in the design tasks listed inA.2.Design reports will be due according to the schedule in tableA.1. The design reports shall follow this format:

• Introduction. An introductory section shall outline the basic issues being addressed in the report. Forexample, Design Report II will address seepage through the retaining levee.

• Analytical model. This section shall present the geometry and material properties for the sectionthat is to be analyzed. For example, a presentation of the seepage model in Design Task II shouldinclude a description (including a sketch) of the levee embankment and the underlying foundation, theboundaries of the various soil types within the levee and foundation, and the permeability of each soiltype.

• Analytical methods. This section shall state and briefly describe the methods used in the analysis. Forexample, two analysis methods will be used for the seepage analyses in Design Task II: flow nets andfinite element analyses.

• Discussion. This section shall report the outcome of the analyses (seepage quantities, foundationsettlements, etc.) In cases where more than one type of analysis is performed, the results should becompared and discussed. Uncertainties in the analysis, and how such uncertainty may be reduced,may also be discussed here.

• Conclusion. The implications of the analyses should be discussed here. For example excessive settle-ment could lead to overtopping and failure of the levee. If the analyses suggest inadequate performanceof the levee, suggested modifications to the design should be presented.

• Appendices. Supporting information for the design task should be appended to the design report. Forexample, the weekly results for Laboratory Sessions 2, 3, and 4 should be appended to Design ReportI.

Specific topics to be included in the design reports may vary according to the topic under consideration.Students should clarify any uncertainties in reporting requirements with the teaching assistant prior to reportpreparation.

A.3 Project overview

FigureA.1 shows a plan view of the project. A 20-ft high ring levee will be constructed to provide contain-ment for treated effluent from a wastewater treatment plant. To provide access for maintenance, the leveecrown must have a minimum width of 20 ft. The preliminary levee design (Figure 2) calls for landside andwaterside slopes of 3 horizontal to 1 vertical (3H:1V). The levee is to be a zoned embankment comprised ofa “clay” core buttressed by outer zones of sand. The purpose of the core is to provide a seepage barrier to



Figure A.1: Plan View of Water Retention Pond

retain the water in the pond. The purpose of the sand zones is to improve the stability of the embankmentagainst a sliding failure - sands typically have higher shearing resistance than clays. When suitable mate-rials are locally available, zoned embankments are typically the design of choice, since they combine thefavorable water retention properties of clays with the favorable strength properties of sands.

The levee will be founded on a 28-ft deep stratum of what has been visually classified as soft clay.Beneath the soft clay are Pleistocene age deposits comprised of stiff clays and dense to very dense sands.

Clay for the core will be obtained locally from the same clay stratum that comprises the levee foundation.The native clay will be excavated, dried to a water content approximating the optimum water content, andplaced in the core zone. The sand will be obtained from a borrow source located in a stream channel depositapproximately two miles from the site. In-place unit weight and moisture tests in the sand deposit indicatea dry unit weight of 103lb/ft3 and a water content of 9.7%. The volume of available sand from this sourceis uncertain, so the preliminary evaluations must provide reasonably accurate estimates of the sand volumesthat must be excavated from the borrow source.

The geotechnical studies for this project have been divided into four main tasks:

Preliminary evaluations will involve performing index and classification tests on the proposed clay andsand levee embankment soils. Based on these tests, a qualitative assessment will be made regarding thesuitability of these soils for their proposed use in the levee embankment. The preliminary evaluationswill also include compaction tests on the sand. Data from these compaction tests will be neededfor estimating the required volume of sand that must be excavated from the borrow source. Unit



Figure A.2: Preliminary Design of Levee Section



weight measurements from the compaction tests will also be used in later settlement and slope stabilityanalyses.

Seepage studies.Estimates seepage flow rates are needed to verify that water loss from the pond will bewithin acceptable levels. The first stage of the seepage studies will entail permeability test measure-ments supplemented by empirical estimates of permeability based on index properties. These perme-ability values will be utilized in flow net and finite element studies to obtain estimates of water lossdue to seepage.

Settlement studies.Excessive settlement of the soft clay foundation soil can lead to loss of freeboard andultimately to overtopping of the levee. Consolidation tests on the foundation soils will be performed toprovide the necessary material parameters for settlement analyses. Using these parameters, estimatesof levee settlement will be performed using: (1) simplified one-dimensional consolidation settlementanalyses and (2) two-dimensional finite element consolidation analyses.

Slope stability. Stability analyses are required to verify that the shear strength of the levee embankmentand foundation soils are capable of resisting the gravitational loads caused by the weight of the addedembankment. The stability studies will entail: (1) laboratory measurements of the shear strengthproperties of the levee embankment and foundation soils, and (2) slope stability analyses to evaluatethe factor of safety against a slope failure.

A.4 Part I

This part of the project involves preliminary evaluation of the soils proposed for levee embankment con-struction. Laboratory Sessions 2 through 4 involve a series of index property and compaction tests on whichthe preliminary evaluation will be based. Tests will be performed a sand proposed for the outer zones (shell)of the levee. The tests series includes the following:

Laboratory Session 2: Sieve analysis of proposed levee shell material.

Laboratory Session 3: Liquid limit and plastic limit of proposed shell material. Visual classification ofproposed shell materials. Hydrometer analysis of proposed shell material.

Laboratory Session 4: Standard Proctor compaction test on proposed levee shell material. Filter papersuction test on proposed levee shell material.

The gradation curve information for the existing soil, the soft marine clay, is included here in TableA.3.This soil has a plastic limit of and a liquid limit of .

Reporting shall be in accordance with the requirements outlined in the project overview. Specific infor-mation to be reported includes:

• Classification of the proposed soils according to the Unified Soil Classification System.

• An assessment of the suitability of the soils for levee construction.

• An estimate of the volume of levee shell (sand) material that must be excavated from the borrow area.This estimate should be based on (1) the computed volume of the levee shell, (2) the compacted unitweight of the levee shell material, and (3) the measured unit weight of the sand in the borrow area.



Particle diameter Percent Finer(mm) (%)0.0782 90.060.0562 86.850.0402 83.630.0331 82.020.0291 78.800.0223 56.290.0174 25.730.0124 22.510.0091 19.300.0065 16.080.0031 9.650.0015 6.43

Table A.3: Gradation curve for the existing marine clay (from CVEN 649 class of 2004).

A.5 Part II

This part of the project involves seepage analysis of the levee embankment. The seepage analysis involvesmeasurement of hydraulic conductivity and prediction of the flow through the levee embankment.

Points to be covered in your design report include the following:

1. Your introductory section should discuss the purpose of the seepage evaluation. Since water loss froma water-retaining structure must necessarily be limited to acceptable levels, a chief concern in this caseis the rate of seepage loss through the levee.

2. The clay in both the levee core and in the foundation is assumed to have a hydraulic conductivityof 8 × 10−5m/day. The sand in the levee shell is assumed to have a hydraulic conductivity of8 ×10−3m/day. Using the guidelines outlines in TableA.4, comment on whether you believe these valuesare reasonable.

3. Your first flow analysis will use a graphical flow net solution. In principle, flow nets can be constructedfor non-homogeneous soil conditions, but the process is quite tedious and time-consuming. Sincethe sand hydraulic conductivity exceeds that of the clay by 2 orders of magnitude, a very good firstapproximation is to consider the sand as “free-draining”, i.e., to have infinite hydraulic conductivity.Your flow net should therefore be drawn for conditions similar that shown in FigureA.3. Constructinga flow net through an embankment also requires some estimate of the water (phreatic) surface. Anestimated phreatic surface is given to you in FigureA.3.

4. Your second flow analysis will be a numerical analysis using the program Plaxis. Instructions forPlaxis are given in Chapter11of the laboratory manual. Analysis of non-homogeneous soil conditionsis relatively straightforward using Plaxis. Therefore, your Plaxis analysis should input actual valuesof hydraulic conductivity for the clay and sand, and need not make the simplifying assumptions thatwere made for your flow net analysis.

5. Both flow net analyses and numerical solutions will provide seepage estimates in terms of flow rate perunit length of levee (e.g.,m3/day/m). While technically correct, seepage estimates presented in thisformat will probably mean little to a project planner. Seepage rates should therefore be presented in a



Soil Coefficient of Permeability, k (m/sec) Relative Permeabilitygravel > 10−3 High

sandy gravel, clean sand, fine sand 10−3 to 10−5 Mediumsand, dirty sand, silty sand 10−5 to 10−7 Low

silt, silty clay 10−7 to 10−9 Very Lowclay < 10−9 Practically Impermeable

Table A.4: Coefficient of permeability. From Electric Power Research Institute, EPRI EL-6800, 1990.

more useful format, such as the daily rate of water loss expressed as a percentage of the total volumeof water retained by the ring levee.

A.6 Part III

This part of the project involves prediction of consolidation settlement of the clay foundation due to the addedweight of the levee embankment. Settlement is critical to the performance of a water-retaining structure, asexcessive loss of freeboard can lead to overtopping and breaching of the structure. Differential settlement canalso lead to cracking of the embankment. In addition to concerns for settlement, the consolidation processin soft clays is often closely monitored to ensure that the rate of embankment construction proceeds at a safepace.

A.6.1 Planned Construction Sequence

Abrupt application of a load to a soft clay stratum can lead to a bearing failure; i.e., the stresses due to theapplied load exceed the strength of the clay, resulting in a catastrophic failure. For this reason, constructionon soft clays is often performed in incremental stages. Application of the first load increment inducesconsolidation. As consolidation occurs, water is expelled from the pores thereby making the clay denser andstronger over time. As the clay gains sufficient strength, it becomes safe to apply the next load increment,and so on. The proposed construction plan for this project calls for the levee embankment to be constructedin three 6.67-ft high stages as indicated in TableA.5.

A.6.2 Construction Monitoring

The progress of consolidation during embankment construction is monitored by two types of measurements:(1) ground surface settlements versus time, and (2) pore water pressure measurements in the clay stratum.In this project, the ground surface settlement will be measured using settlement plates embedded at thecenterline of the embankment, and the pore water pressure will be measured by piezometers installed at mid-depth of the clay layer (figureA.4). Normally the geotechnical engineer will make predictions of settlementsand pore water pressures versus time that are likely to occur during construction. These predictions provide

Stage Time from Start of Construction (days)1 02 1203 300

Table A.5: Planned Construction Stages



Figure A.3: Model for Flow Net Construction.Texas A&M University G. Biscontin


Figure A.4: Construction Sequence and Geotechnical Monitoring

a basis for evaluating the measurements during construction. If the field measurements significantly deviatefrom predictions, the rate of construction is slowed down or accelerated accordingly.

A.6.3 Analyses

As the geotechnical engineers on this project, your task is to provide predictions of (1) ground surfacesettlements that will occur over time at the centerline of the embankment, and (2) pore water pressures thatwill occur over time in the piezometer installed at mid-depth of the clay layer. Conceptual sketches of whatthese predictions should look like are shown in FiguresA.5 andA.6, respectively. Note that settlementscontinue after excess pore pressures decline to zero due to secondary compression. Your predictions for bothsettlements and pore pressures should be based on two analyses:

One-Dimensional Approximation Although the actual problem involves consolidation in two-dimensions,the one-dimensional consolidation calculations discussed in the lectures and text can provide reason-able first order predictions of settlements and pore pressures. Specific calculations that you must makeinclude the following:

• The magnitude of primary consolidation settlement is estimated using the one-dimensional ap-proximation. Due to the non-linearity of these equations, the 28-foot clay layer should be sub-divided into four 7-foot sub-layers for settlement calculation purposes. You may also assume



Figure A.5: Conceptual sketch of settlement predictions.

that the embankment load can be approximated as a uniform load of infinite lateral extent; i.e.,the change in vertical stress due to the embankment load is the same at all depths within the claylayer (∆σz = γfilldfill). Finally, you may assume that the clay layer is normally consolidated

• The time rate of primary consolidation settlement is estimated using the solution to the consoli-dation equation (depicted graphically in Figure 7.18, curve 1 of Craig). You may assume doubledrainage in the clay layer for these calculations.

• The rate of secondary compression settlement is estimated usingCα. You may assume thatprimary consolidation is effectively ended when the dimensionless time factor T=1.0.

• Pore water pressures versus time at mid-depth of the clay layer are estimated using the solutionto the consolidation equation (depicted graphically in the handout distributed in class).

Two-Dimensional Analysis As noted above, the actual problem is more realistically represented as a two-dimensional problem. Two-dimensional analytical solutions for consolidation usually become in-tractable for all but a few simple cases. However, numerical analyses can effectively model theconsolidation process. The computer program Plaxis performs such numerical analyses. A detaileddescription of consolidation analyses using Plaxis is provided in Chapter 14 of the Laboratory Manual.

A.6.4 Laboratory Test Interpretation

Laboratory test procedures for determining the material parameters required for a consolidation analysis aredescribed in Chapter 13 of the Laboratory Manual. The consolidation test will provide a total of 5 param-eters. Three parameters provide the data necessary for estimating the magnitude of primary consolidationsettlement: the recompression indexCr (equal to the swell indexCs), the compression indexCc, and the pre-consolidation stressσ′

c. The consolidation test also provides estimates of two parameters for characterizingthe time rate of settlement: the coefficient of consolidationcv and the coefficient of secondary compressionCα. The Plaxis program uses essentially the same five material parameters as the one-dimensional calcula-tions, although the Plaxis defines the parameters slightly differently. Conversion of the material parametersto a form suitable for Plaxis is described in Chapter 14 of the Laboratory Manual.



Figure A.6: Conceptual sketch of pore water pressure predictions


geotechnical eng. lab manual

Documents

required materials

standard reference

visual classication

standard effort

plasticity index of

test specimen

initial classication

fundamental test conditions