geotechnical design guidelines -...

GEOT

CAW

JABATAN KERJA RAYA MALAYSIA

Guideline for Soil Investigation Works on Soft Ground

Guideline for Preparation of Site Investigation Report

Guideline for Preparation of Geotechnical Evaluation and

Design Report

Geotechnical Analysis

Pile Foundation Design

Geotechnical Design Checklist

ECHNICAL DESIGN GUIDELINES

UNIT MARITIM ANGAN PANGKALAN UDARA DAN MARITIM

IBU PEJABAT JKR MALAYSIA KUALA LUMPUR

Maritime Unit Geotechnical Design Guidelines

TABLE OF CONTENT

Page

TABLE OF CONTENT

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CHAPTER 1 GUIDELINE FOR SOIL INVESTIGATION WORKS ON

SOFT GROUND

1.0 Introduction

1.1 Desk Study

1.2 Scope of Site Investigation

1.2.1 Embankment on Soft/Weak Ground

1.2.2 Site Investigation for Structure

1.3 Procedure

1.4 Common Site Investigation Methods

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CHAPTER 2 GUIDELINE FOR PREPARATION OF SITE

INVESTIGATION REPORT

2.0 Introduction

2.1 Soil Investigation Report Requirements

2.1.1 Authentication of the Factual Report by SI

Consultant/ Contractor

2.1.2 Introduction

2.1.3 Site Description

2.1.4 Method Statement of SI

2.1.5 Field Investigation Results

2.1.6 Laboratory Test Results

2.1.7 Summary of Laboratory Test results

2.1.8 Drawing and Photograph

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CHAPTER 3 GUIDELINE FOR PREPARATION OF GEOTECHNICAL

EVALUATION AND DESIGN REPORT

3.0 Introduction

3.1 Geotechnical Evaluations

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3.1.1 Define Subsoil Profile

3.1.2 Interpretation of Lab and In-Situ Test Results

3.1.2.1 Laboratory Test

3.1.2.2 In-Situ Test

3.1.3 Description of Soil/ Rock Properties

3.1.3.1 Engineering Properties of Soils

3.1.3.2 Engineering Properties of Rocks

3.1.4 Selection of Geotechnical Parameters

3.2 Recommendations on Geotechnical Design

3.2.1 Slope stability

3.2.2 Retaining Walls

3.2.3 Embankment

3.2.4 Drainage

3.2.5 Basement

3.2.6 Piles

3.2.7 Ground anchors

3.2.8 Tunnels and underground works

3.2.9 Safety of neighbouring structures

3.2.10 Monitoring of movements

3.2.11 Chemical attack

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CHAPTER 4 GEOTECHNICAL ANALYSIS

4.0 Introduction

4.1 Stability Analysis

4.1.1 General

4.1.2 Methods of Analysis

4.1.3 Required Safety Factors

4.1.4 Effects of Soil Parameters and Groundwater On

Stability

4.1.5 Slope Stabilization

4.2 Settlement Analysis

4.2.1 General

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4.2.2 Settlement Predictions and Calculation of Settlement

Times

4.2.3 Design Criteria for Settlement Analysis

4.2.4 Ground Improvement Methods of Reducing or

Accelerating Settlements

4.2.4.1 Preloading

4.2.4.2 Vertical Drain

4.2.4.3 Removal of Compressible Soils

4.2.4.4 Balancing Load by Excavation

4.2.4.5 Others

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CHAPTER 5 PILE FOUNDATION DESIGN

5.0 Introduction

5.1 Pile Design Procedures

5.2 Selection of Pile Types

5.3 Pile Design Criteria

5.3.1 Recommended Factors of Safety

5.4 Estimate of Pile Capacity

5.4.1 Use of Soil Mechanics Principles

5.4.2 Correlation With Standard Penetration Test (SPT)

5.5 Negative Skin Friction

5.5.1 Calculation of Negative Skin Friction

5.6 Settlement of Pile or Pile Group

5.6.1 Settlement of an Individual Pile in Clay

5.6.2 Settlement of Piles Within a Group In Clay

5.6.3 Settlement of An Individual Pile In Sand or Gravel

5.6.4 Settlement of A Pile Group In Sand or Gravel

5.6.5 A Simple Method of Estimating The Settlement of A

Pile Group

5.7 Structural Capacity of Piles

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GEOTECHNICAL DESIGN CHECKLIST


Stability Analysis Checklist

Settlement Analysis Checklist

Ground Treatment Design Checklist

Foundation Design Checklist

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APPENDIX

1 - List of Lab and In-Situ Test

2 - List of Abbreviations/ Symbols

3 - Applicability of Common Field or In-Situ Tests

4 - Common Samplers

5 - Quality of Samplers (After Rowe)

6 - Summary of Scope of SI works

1a - Flow Chart For Geotechnical Design Works

1b - Flow Chart For Site Investigation Works

1c - Flow Chart For Stability Analysis

1d - Flow Chart For Settlement Analysis

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Maritime Unit Guideline for Soil Investigation Works on Soft Ground

CHAPTER 1

GUIDELINE FOR SOIL INVESTIGATION WORKS ON SOFT GROUND

1.0 INTRODUCTION

The basic purpose or objective of site investigation is to acquire all necessary ground

information and data to enable a safe, practical and economical geotechnical or foundation design to be prepared.

Site investigation is an essential part of the geotechnical design process. Intimate

knowledge of the test methods and possible geotechnical problems that can arise from ground conditions with particular reference to problems on stability and deformation or displacement of slopes and foundations are essential for planning the scope of site investigation (SI) works.

This guideline is intended to assist engineers to plan and implement site investigation

(SI) works for marine projects so as to ensure that the SI results are complete, adequate, accurate and reliable according to usual good engineering practice. Sound knowledge of SI methods, in-situ and laboratory testing, equipment, procedures coupled with understanding of typical potential geotechnical problems for marine works will ensure proper SI methods and appropriate tests for the situation are selected to achieve the targeted purpose of SI.

This guideline also identifies the typical geotechnical issues or problems for

construction of embankment and common marine structure in typical geological formations. Scope of SI and suitable SI methods including relevant types of field tests, samples and laboratory tests to procure the appropriate design parameters for the geotechnical problems identified are subsequently discussed. General procedure of SI works including preparation of SI report is also included. Decision making process of SI is presented by the flow chart in Appendix 1a which indicated the stages of an investigation, the action required, and those who should have responsibility for carrying out the actions.

The planning of SI works should be carried out by suitably qualified geotechnical

engineers after review of the project brief/ location, desk study and field inspection. All the quality SI works should be closely directed, monitored, supervised and reported by qualified geotechnical engineers registered with Board of Engineers Malaysia.

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1.1 DESK STUDY

Before planning for site investigation (SI) works, the following desk studies should be carried out first:-

• Project brief with site and location plan (to check overall details of structure and nature of project; loads, bearing capacity, settlement and stability requirement of slopes, walls, bridges and others superstructures). Usual geotechnical design criteria for marine works are shown in Appendix A.

• Topo map (to assess terrain, access and site/ environment conditions).

• Geological map (to evaluate geological formation and characteristics).

• Aerial photo (to study site conditions, land used etc.)

• Other relevant records and information.

• An evaluation of performance of existing structure in the immediate vicinity of the

proposed site, relative to the foundation, material and environment.

• A review of all available information on the geologic history and formation of rock, or soil or both and ground-water conditions occurring at the proposed site or location and in the immediate vicinity.

These information plus site reconnaissance or walk-over survey by designer or

engineers involved in SI is crucial to obtain basic knowledge of site condition and project concept designs. The need, purpose and the likely geotechnical issues or problems can then be identified and subsequently used to determine or design the scope and methods of SI works. Through SI, the knowledge of behaviour of the ground and its spatial variability can be obtained for the necessary geotechnical design and construction. 1.2 SCOPE OF SITE INVESTIGATION

Scope of SI for a project depends on what is known about the site and what geotechnical data are required for geotechnical design or evaluation of geotechnical issues or problems. The following information has to be procured before scope of SI can be planned:

• Likely or possible or anticipated geotechnical issues or problems to be encountered in

design and construction • Establish to purpose and need of SI

• What information is required

• Extent, areas and depth of ground to be investigated

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• Time and site constraint

The extent of SI mainly depends on the character and variability of the subsoil and ground water and the amount of existing information available. However, it should be noted that subsoil conditions of a site are very sensitive to geological conditions and so the spacing and location of boreholes/ test pits/ types of tests should be more closely related to the detailed geology of the project area and the geotechnical problem/ analysis required to be carried out.

Common SI methods and list of relevant lab and field test methods are given in

Appendix 1. List of abbreviations used is given in Appendix 2. Some typical geotechnical problems and usual applicable SI methods and tests for typical marine works are given in the following sections.

1.2.1 Embankment on Soft/Weak Ground

Coastal alluvium or deposited soil formations or swamps are typical soft/ weak grounds. Typical geotechnical problems in such areas are settlement and stability. Usual geotechnical design and checking are bearing (short and long term), slope stability (local and global, short and long term), amount and rate of settlement (primary and secondary consolidation, elastic deformation). Geotechnical design are usually carried out to check weather the design criteria as shown in Appendix A can be complied and subsequently carry out the necessary designs of ground improvement works. Important data to be acquired through SI are:

1. Subsoil profile showing the thickness of various compressible and firm strata, water

table etc. Deep Sounding/ Deep Boring (DS/ DB) plus continuous sampling are necessary if accurate profile is required. Spacing of DS/ DB should be in the range of 60m to 300m. DS/ DB can be supplemented by Geonor Vane tests and JKR probes. Usually one or two boreholes plus two or more DS or piezocones are used to determine the generalized subsoil profile for each stretch of soft ground. Criteria to terminate depth of borehole are:

a. Until 10 SPT exceeding 10 or until 10 in-situ vane shear tests exceeding 50

kPa if the height of embankment is less than 3m b. Until 5 SPT exceeding 20 or 5 in-situ vane shear tests exceeding 75 kPa if the

height of embankment is 3m to 5m.

c. Until 2 SPT exceeding 50 or 2 SPT exceeding 40 (for depth exceeding 30m) if the height of embankment is more than 5m.

d. At least one borehole along the soft stretch should be extended until 2

consecutive SPT exceeds 50 or until 1.5 m rock coring, whichever come first.

2. Consolidation parameters for settlement analysis (Cc, Cv, Mv, Pc etc from consolidation tests using quality undisturbed samples obtained by stationary piston

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samplers). These consolidation properties also can be supplemented by correlation values from DS or piezocones tests.

3. Shear strength parameters for stability and bearing analysis or ground improvement

design (Cu from in-situ vane shear tests or undisturbed samples, C’ and ∅’ from triaxial tests using quality undisturbed samples….)

4. Index properties (LL, PL, PI, M/C, gradation, organic content etc) for soil classification and engineering property correlations etc.

5. See Appendix 3 for applicability of various tests for various engineering properties.

1.2.2 Site Investigation for Structure

Purpose of SI for structures such as bridges, walls, major culverts etc are for foundation design and construction with particular reference to capacity, settlement and constructability assessment.

At least 2 DB should be carried out at each site or minimum one DB per pier/

abutment or one DB per 60m spacing especially for erratic or unstable geological formation areas (limestone, boulder abundant areas, faulted/ sheared zone etc). Borehole could be terminated after 5 consecutive SPT exceeding 50 or 10 consecutive SPT exceeding 30 if the borehole depth is more than 60m or refer to designer for direction. If rock is encountered coring shall be carried out and minimum core length depends on type and condition of rock. Suggested minimum core length is as in Table 1.1.

Table 1.1: Suggested minimum core length

Rock Type Min. Core Length

Igneous rock (granite) and bore depth < 24m or recovery ratio R/r < 50% 4.5m

Igneous rock, bore depth > 24m 3.0m Shale/ schist/ slate/ sand-stone, recovery ratio R/r < 50% 6.0m Shale/ schist/ slate/ sand-stone, recovery ration R/r > 50% 3.0m Limestone R/r > 50% and no cavity 6.0m Limestone R/r < 50% or with cavity 9.0m-21.0m Other rocks R/r > 50% 4.5m Other rocks R/r < 50% 6.0m

For structures on soft ground, in-situ vane shear tests and undisturbed sampling for shear strength and consolidation tests should be carried out. These tests results are necessary for foundation design, stability analysis, and construction/ temporary works design. Pressuremeter and plate bearing tests may be specified if detail fractured rock conditions (stiffness and deformation) are required for bearing design e.g. rock socket design or shallow foundation design. See Appendix 3 and 4 for additional guidance. Preparation of “Summary of Scope of SI Works” and an illustrated example are enclosed in Appendix 5.

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1.3 PROCEDURE

1. The guidance given in Para 3 above can be used to determine the locations, numbers and types of SI methods or boreholes or in-situ testing required basing on the need and purpose of SI established from the desk study. Size of boreholes depends on the size of soil and rock samples required. Size of samples depends on types of soils/ rocks and types of tests required.

Common SI methods are JKR Probes, HA, MHB, DB, DS (10T/ 20T), Piezocone, Bulk Sampling, Test Pits, Geonor Vane, continuous soil sampling, SBP, seismic surveys, etc. Methods, procedure and equipment for SI methods and testing should comply with standard JKR SI Specification and relevant MS/ BS/ ASTM standards. Standard borehole or casing sizes commonly used are 75 mm, 100 mm, 150 mm. Usually size NW casing or borehole is specified for DB except when extensive and high quality large undisturbed samples are required to determine accurate consolidation properties and shear strength for stability and settlement analysis. Guidance on selection of SI methods, spacing and depth of boreholes, types of field and lab tests etc has been discussed. Appendix 3 and 4 also provide some guidance in specifying the methods of sampling and applicability of common field tests.

2. The sequence of SI methods or boring or in-situ testing and criteria of termination of

boreholes should be clearly stated in the document for SI contractor. Phasing of SI programmed may be necessary for large/ complicated projects (Preliminary and detail SI works).

3. Some guidance to determine the frequency and types of in-situ testing/ sampling in the

boreholes are:

a. Vane shear test

i. Very suitable for very soft to stiff clay to obtain undrained strength.

b. Standard Penetration Test (SPT)

i. Suitable for almost all soil types except very soft clay and coarse gravel; disturbed samples (35 mm diameter) are procured from the test for field identification/ description of soil types and subsequent lab classification and index properties tests. SPT is usually carried out at a change of strata or 1.5 m interval except when undisturbed sampling or vane shear test or pressuremeter test is required. SPT may be carried out at 1.0 m interval if detailed information is required e.g. for shallow foundation and deep excavation works.

c. Pressuremeter test

i. Menard or self Boring type; suitable for most soil types and soft rocks except soft organic soil and hard rock; useful to obtain accurate bearing capacity, stiffness and compressibility properties; costly and slow test;

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usually carried out only when quality undisturbed samples or disturbed samples are difficult to procure but important for the design e.g. highly fractured soft rock, sandy material etc.

d. Packer test

i. Single or double Packer test is sometimes carried out in rock strata to assess the amount of grout that rock will accept, to check the effectiveness of grouting, to obtain a measure of fracturing of rock, to give an approximate permeability of rock.

e. Undisturbed sampling

i. Thin wall open tube sampler, 50 mm, 75 mm, or 100 mm diameter; area ratio is about 10%; suitable for soils having some cohesion unless they are too hard or too gravelty.

ii. Stationary piston thin wall sampler 50 mm, 75 mm, or 100 mm

diameter; suitable for very soft to firm clay when strength and consolidation properties are required.

iii. Denison sampler for stiff to very stiff cohesive soils and sandy soils

(SPT = 4 to 20).

iv. Quality requirement of samples (Appendix 6).

v. Mazier sampler, 50 mm and 74 mm diameter; suitable for residual soil when strength tests are required; careful air foam drilling technique is preferred to ensure high sample quality.

vi. Delft (29 mm or 66 mm diameter) or Swedish (68 mm diameter)

continuous soil samplers for soil fabrics and stratigraphical / profiling evaluation.

4. If rock is encountered or rock coring is required, determine the size, length and type of

coring (or criteria of coring).

a. Double tube swivel type (30 mm, 42 mm, 54 mm diameter, TNW 61 mm diameter) could be used in most rocks.

b. Triple tube core barrels (NMLC, 52 mm diameter or HMLC, 64 mm diameter)

should be used for weak, weathered or fractured rocks. c. Wire line barrels for rock coring at great depth. d. BW or larger drill rods are preferred if bore depth exceeds 20 m.

5. Prepare BQ, Specification, Costing and Works programme (Standard JKR BQ and

Specification should be used).

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6. Determine procedure, extent of supervision and monitoring of SI works (supervisor and drillers should have CIDB certificates).

7. The proposed scope of SI should be checked or audited by an expert before

implementation. Ensure reliable/ reputable SI contractor registered with CIDB is engaged. Checked the proposed works programme and ensure all equipment proposed comply with relevant standards.

8. Determine scheme of laboratory testing including types of lab tests for:

a. Disturbed samples (mainly for basic and index properties tests) Soil

classification tests shall be carried out for all typical disturbed samples at various distinct strata.

b. Undisturbed samples (mainly for engineering property tests). c. Water samples (mainly for chemical tests). At least 3 water samples from river

for bridge project shall be taken for chemical tests (pH, SO4, Chloride etc).

d. Block samples (mainly for engineering property tests).

e. Bulk samples (mainly for compaction/ CBR tests plus classification tests).

9. Usual important laboratory tests:

a. Important geotechnical properties from laboratory tests are:- i. BASIC PROPERTIES (colour, natural moisture content, sg, porosity,

void, reactivity etc.) for soil description, classification and correlations. ii. INDEX PROPERTIES (LL, PL, PI, SL, particle size distribution,

organic content etc) for soil description, classification and correlations with engineering properties.

iii. CHEMICAL PROPERTIES (total dissolved salts, sulphate and chloride contents; pH value etc) for corrosion and durability assessment of foundations.

iv. ENGINEERING PROPERTIES (shear strength, stiffness, compressibility, compaction/ CBR, permeability etc.) for analysis and design. Engineering properties can be obtained from in-situ testing and laboratory tests on undisturbed samples. The results from the in-situ and laboratory testing should be viewed as complimentary and then compared with the recommended data from the published literatures before adopting as design parameters. For uniform subsoil, more elaborate lab testing should be done, but if the subsoil is complex or erratic, more in-situ testing is more meaningful.

b. Classification and index tests from disturbed and undisturbed samples are

mainly for classification, identification and simple preliminary correlations for shear strength parameters and other engineering properties/ behaviour.

c. Shear strength tests from block samples and undisturbed samples (UU, CU,

CKUC, CIUC, CIUE, CD triaxial tests, direct shear test, UCS etc.) are for

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analysis and design.

d. Consolidation and permeability tests from undisturbed samples or block samples are for settlement analysis and seepage evaluation.

e. Compaction/ CBR tests from bulk samples coupled with index properties are

for fill suitability evaluation and stability analysis etc. 1.4 COMMON SITE INVESTIGATION METHODS

SI method and the type of equipment or sampler required for a SI job depend on the nature of terrain, access, type of geological formation and intended used of the data.

Experience plus engineering judgement are required in selection of SI method.

Common SI methods are briefly outlined as follows: 1. JKR Probes

Results can be used to determine thickness of unsuitable material to be removed and also for preliminary design of embankments. Usually carried out near HA or DB positions and filling areas to verify the consistency of subsoil of medium strength up to maximum of 12 m deep.

2. Hand Augering (HA)

HA Used in soft to stiff cohesive soils or sandy soils above water table. Usual spacing is 60 m – 600 m. Maximum depth is about 5 m. Very extensively used for road projects because extensive open tube samples of 50 mm to 100 mm diameter along the alignment can be obtained at a relatively fast and low price for the basic and index properties; used for identification, classification and correlation of engineering properties such as permeability, strength and deformation etc. HA is particularly valuable in connection with ground – water determination.

3. Deep Boring (DB)

Borehole should be advanced by power rotary drilling with adequate capacity for the specified depth of drilling i.e. open hole rotary drilling or casing advancement drilling method. To avoid disturbance of the underlying soil stratum, only side discharge of flushing medium (water) from drilling rod bits is allowed; bottom discharge from casing should not be permitted. Borehole size of NW or HW is preferred. For borehole deeper than 20 m, rods with stiffness equal to or greater than BW drill rods but less than 10 kg/m should be specified. DB is invaluable to determine stratigraphical formation and subsoil properties in cut and filling areas. Usual spacing is 60 m – 600 m. Field tests such as SPT, vane shear, (for soft to stiff strata) permeability and pressuremeter tests can be carried out in the boreholes. Disturbed and undisturbed samples can be taken for various laboratory tests to

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determine strength and deformation properties. Piezometers can also be installed in the borehole to monitor the ground water conditions. SPT tests are usually carried out at 1.5 m interval. For soft clay and residual soils strata, stationary piston and Mazier samplers are respectively used to take quality undisturbed samples for laboratory strength tests. Continuous soil sampling (Swedish or Delft Samplers) is specified if identification of soil fabric or depth of changes in distinct strata and properties are required. For uniform subsoil, more sampling for lab tests; but for erratic subsoil more field tests should be carried out.

4. Deep Sound (DS) – 100 kN/ 200 kN capacity

This is the static Dutch Cone Penetrometer Test. It is usually used to supplement Deep Boring results in filling areas which are fluvial or soft formation. Not suitable for boulder or gravel abundant subsoil. The results can be used to correlate and ascertain strength and deformation properties etc. of the subsoil. Useful and adequate to determine subsoil profile. A Piezocone test is preferred.

5. Test Pits, Bulk Samples and Block Samples

Usually test pit can be up to 2 m deep. Visual inspection of subsoil strata, soil type and strength (by pocket penetrometer) can be carried in test pit. Bulk samples (about 50 kg) for lab tests (soil classification, CBR and compaction tests) can be collected. Undisturbed block samples also can be obtained for strength tests in the laboratory.

6. Motorised Hand Boring (MHB)

MHB or commonly called wash boring or percussion drilling consists of a tripod with block and tackle or motor driven winch. The borehole is advanced by chopping while twisting rods and washing with pump – circulated water. It is simple, portable and can be used in all types of soils except those containing big boulders. Progress is slow when encountering very stiff/ dense material especially when deeper than 10 m. MHB can be adopted easily at locations where access is difficult. Normally casing is used and maximum depth of boring is about 20 m. SPT, vane shear test and undisturbed sampling (only soft to medium soil) can be carried out in the borehole at the required depth.

7. Geophysical Survey

Sometimes geophysical survey is used to supplement borehole results. The seismic refraction method with multigeophones reception of seismic wave of signals originating from explosives or hammer blows (for shallow investigation only) can be used to determine the approximate rock profile and geologic features e.g. faults etc. The electrical resistively method for measuring the resistance of soil to a direct or alternating current is also useful in determining depth to rock, evaluating stratified formations where a denser stratum overties a lesser dense stratum. Corrosively of soil and geological features and cavities can also be determined.

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Maritime Unit Geotechnical Design Guidelines - Appendix 1

LIST OF LAB AND IN-SITU TESTS

1. Soil Classification Tests: BS 1377 : Part 2 : 1990

Moisture content, Liquid limit, Plastic limit, Plasticity index, Linear shrinkage, particle size distribution. {These tests are from disturbed samples such as split spoon samplers (SPT), bulk samples etc).

2. Chemical and Electro-chemical tests : BS 1377 : Part 3 : 1990

Organic matter content, Mass loss on ignition, Sulphate content of soil and ground water, Carbonate content, Chloride content, Total dissolved solids, pH value, Resistivity and Redox potential.

3. Compaction -related tests: BS 1377 : Part 4 (These tests are from bulk samples)

3.1 Dry density - Moisture relationship (2.5 kg/ 4.5 kg hammer)

- Soil with some coarse gravels - Vibrating method

3.2 Moisture condition value (MCV) 3.3 CBR tests.

4. Compressibility, Permeability and Durability Tests: BS 1377: Part 5

4.1 1-D consolidation test 4.2 Swelling and collapse tests 4.3 Permeability by constant head 4.4 Dispersibility

5. Consolidation and Permeability Tests in Hydraulic Cells and with pore pressure measurements : BS 1377 : Part 6

5.1 Consolidation properties using hydraulic cell 5.2 Permeability in hydraulic conso cell 5.3 Isotropic conso properties using triaxial cell 5.4 Permeability in a triaxial cell

6. Shear Strength Tests (Total Stress) BS 1377 : Part 7

6.1 Lab vane shear 6.2 Direct shear box (small) 6.3 Direct shear box (large) 6.4 Residual strength 6.5 Undrained shear strength (UU) 6.6 Undrained shear strength (multi loading)

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7. Shear Strength Tests (Effective Stress) BS 1377: Part 8

7.1 CIU with pore pressure measurement 7.2 CD with pore pressure measurement

8. In-situ Tests: BS 1377 : Part 9

Field density (cone, sand replacement and balloon), CBR, SPT, Plate bearing, Vane shear (Acker, Geonor, Cylindrical), DS (Static Dutch cone), Piezocone Test, etc.

Note:

* These tests are .from undisturbed samples (thin wall samples, Mazier samplers, block samples-etc)

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LIST OF ABBREVIATIONS/ SYMBOLS

ASTM = American Society for Testing and Materials BS = British Standard BQ = Bills of Quantities Cc = Compression Index Cv = Coefficient of Consolidation Ci = Effective Cohesion Cu = Cohesion CBR = California Bearing Ratio CIDB = Construction Industry Development Board CU = Consolidated Undrained Triaxial Test CD = Consolidated Drained Triaxial Test CIUC = Consolidated Undrained Compression Triaxial Test with Pore

Pressure Measurement (Effective stress) ClUE = -Ditto -extension CkoUC = Consolidated Undrained Compression at Ko Conditions DB = Deep Boring {rotary drilling) DS = Deep Sounding (Static Dutch Cone Penetrometer) GL = Ground Level. HA = Hand Auger HMLC = 65mm Triple Tube Core Barrel (DCMA) JKR = Jabatan Kerja Raya LL = Liquid Limit M/C = Moisture Content Mv = Coefficient of Compressibility MHB = Motorized Hand Boring (Wash Boring/ Percussion Drilling) MS = Malaysian Standard NW = N Size Casing (101.6mm diameter) NMLC = 52 mm Triple Tube Core Barrel (DCMA) pH = Acidity Index PL = Plastic Limit PI = Plasticity Index Pc = Effective preconsolidated Pressure RL = Reduced Level RQD = Rock Quality Designation R/r = Recovery Ratio SI = Site Investigation SPT = Standard Penetration Test TNW = 61mm Double Tube Core Barrel (Atlas Copco) UU = Unconsolidated Undrained Test gives undrained shear strength (Total

Stresses) UCS = Unconfined Compression Strength WT = Water Table

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APPLICABILITY OF COMMON FIELD OR IN-SITU TESTS

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COMMON SAMPLER

TYPES OF SAMPLERS REMARKS

1. OPEN DRIVE SAMPLERS 1.1 Split-spoon for SPT 1.2 Thin-wall sampler 1.3 Thick Wall sampler (50mm, 75mm, I00mm, 150mm).

1. No piston; penetration by static thrust or dynamic impacts; suitable for almost all types of soils except gravelly soils or hard/ dense materials

2. THIN-WALL SAMPLER WITH STATIONARY PISTON (50mm, 75mm, 100mm, 150mm)

2. The most reliable sampler to procure undistributed soft to stiff cohesive soils; area ratio is usually about 10%. The inside clearance ratio shall be 0.5 to 1%. Mainly for shear strength & consolidation tests.

3. DENISON SAMPLER (Double tube with thin wall tube)

3. No piston; suitable for stiff to very stiff cohesive soil and sandy soil (SPT = 4-20); open driver sampler

4. MASIER SAMPLER (74mm)

4. Triple tube sampler; usual core size 74mm diam & PW casing is required; air foam drilling techniques is preferred to procure high quality undistributed samples from residual soils. Not suitable for gravely soils.

5. SOIL CONTINUOUS SAMPLERS (DELFT 29mm, 66mm, OR SWEDISH SAMPLER 68mm diam}

5. With stationary piston; suitable for minor stratification i.e. sand seams because of continuous samples of 5 to 8m can procured.

6. BLOCK SAMPLING

6. Blocks f soil (200mm to 350mm cubes) cut from test pits; Need careful sealing and handling. Mainly for triaxial, shear box & permeability tests.

7. ROTARY ROCK CORE SAMPLERS

7. Double tube core barrels for strong rock (Grade 1 or 2): 30mm; 42mm; 54mm; TNW, 61mm; T2-76, 62mm.

Note: 1. Std. Sampler size (UK): 50, 75, 100, 150, 250mm diam.

Std. Sampler size (US): 1½, 2, 2½, 3, 4, 5 inches diam.

2. Samples should be labelled, handled, transport and extruded carefully in Accordance with BS 5930.

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QUALITY OF SAMPLES (AFTER ROWE)

Quality

Class

Properties Purpose Typical Sampling

Procedure

1 - Remoulded properties - Fabric - Water content - Density and porosity - Compressibility and

deformation - Effective strength parameters - Total strength parameters - Permeability* - Consolidation*

Laboratory data on in-situ soils (Classification tests & engineering properties)

Piston thin walled sampler with water balance Mazier sampler with foam drilling Block samples

2 - Remoulded properties - Fabric - Water content - Density and porosity - Compressibility and

deformation* - Effective strength parameters* - Total strength parameters*

Laboratory data on in-situ insensitive soils

Pressed or driven thin or thick walled sampler with water balance Mazier sampler

3 - Remoulded properties - Fabric A* 100% recovery Continuous B* 90% recovery Consecutive

Fabric examination and laboratory data on remoulded soils

Pressed or driven thin or thick walled sampler. Water balance in highly permeable soils.

4 - Remoulded properties

Laboratory data on remoulded soils. Sequence of strata

Bulk and jar samples (from SPT split samplers)

5 None Approximate sequence of strata only

Washings (washed samplers)

* Items changed from original German classification (7th, Int. Conf. Soil Mech. Found.

Engng. Mexico 1969).

15


SUMMARY OF SCOPE OF SI WORKS

Summary of Scope of SI works should include the following details:

1. Brief project description and objectives of SI.

2. SI Methods & Locations (Scope of SI Works)

- Types & methods SI & the quantities should be indicated - Locations of SI shown on Drawings should be indicated

3. Criteria of Terminating: Boreholes

Criteria of terminating boreholes or other SI methods should be clearly indicated e.g. in cut areas, in fill areas (in soft ground/ swamp and residual soil areas) and in structure areas.

4. Field Testing and Sampling Criteria

Type & frequency of various field tests & sampling should be indicated.

5. Laboratory Testing:

Types of lab testing & the selection criteria should be indicated.

6. Special Requirements

Special requirements about SI methods, testing and sampling if any should be clearly mentioned.

16

Maritime Unit Guideline for Preparation of Site Investigation Report

CHAPTER 2

GUIDELINE FOR PREPARATION OF SITE INVESTIGATION REPORT

2.0 INTRODUCTION

The SI report is intended to define the subsurface conditions and provides geotechnical conclusions and recommendations for design and construction of the project. A geological assessment or engineering geology report may be incorporated into or included as an appendix to the geotechnical soil report for the purpose of providing geologic information for geotechnical engineers, explaining the implications of the subsurface conditions for appropriate project design and construction. 2.1 SOIL INVESTIGATION REPORT REQUIREMENTS

Once the field and laboratory SI works are completed, it is necessary for the designer to ensure that all the information of the SI works to be well documented. In general, this document will be a main reference source and provide the basic guideline for designer to produce a perfect design of project. Most of the soil properties used in geotechnical design can be obtained directly from this report, while the subsurface profile of the site also used to assist designer to identify the most effective construction methods in term of constructability, cost, functionalities etc. Soil investigation report should include but not limited to the following information:-

2.1.1 Authentication of the Factual Report by SI Consultant/ Contractor

The factual SI report should be prepared, checked and certified by a suitably qualified geotechnical engineers or engineering geologist. The SI contractor appointed to conduct any field or laboratory testing must be registered with CIDB. 2.1.2 Introduction

Stated for whom the SI works was done, the nature and scope of SI, purpose of SI and the period the work was done. Brief summary of the proposed project location shall also be outlined.

17

Maritime Unit Guideline for Preparation of Site Investigation Report

2.1.3 Site Description

Describe access condition, terrain and topography, main surface features vegetation; details of existing land use, geological information etc. about the site.

2.1.4 Method Statement of SI

Describe SI methods, sampling methods, testing, procedures, types and models of

equipment used (quote standards used). Standards used in various tests shall also be stated. 2.1.5 Field Investigation Results

The results includes collected data from various field test conducted at the proposed site such as borehole logs, field vane shear test, JKR probe etc. It is necessary to ensure that all of the collected field data must be checked and corrected base on the laboratory test results.

2.1.6 Laboratory Test Results

Completed laboratories test data on soil samples obtained from field exploration must be included in the SI report. Every single page of the lab tests shall also be certified by qualified lab technician etc. 2.1.7 Summary of Laboratory Test results

All of the laboratories test data for soil samples of each borehole has to be summarized accordingly to give some convenience to the designers when references need to be made. 2.1.8 Drawing and Photograph

Includes the location plan showing the boreholes and test locations; photos showing site condition, boring plant set-up, typical samples etc.

18

Maritime Unit Guideline for Preparation of Geotechnical Evaluation and Design Report

CHAPTER 3

GUIDELINE FOR PREPARATION OF GEOTECHNICAL EVALUATION AND DESIGN REPORT

3.0 INTRODUCTION

Analysis of SI results from various tests and field descriptions has to be carried out to detect if there is any discrepancy or some of the results contradict each other. Of course to detect or to identify the discrepancy one needs to know the basics elements of soil mechanics and how the results are obtained from tests. Interpretation of SI results is also a requisite for geotechnical assessment/ evaluation of a site.

3.1 GEOTECHNICAL EVALUATIONS

Geotechnical evaluation includes:

i. Define subsoil profile

ii. Interpretation of lab and in-situ test results

iii. Description of soil properties

iv. Selection of geotechnical parameters 3.1.1 Define Subsoil Profile

For the purpose of analysis, it is frequently necessary to make simplifying assumptions

about the ground profile at the site. These are the best conveyed in a report by a series of cross sections illustrating the ground profile, simplified as required, and showing the ground water levels. The sections should preferably be plotted to a natural scale. If it is necessary to exaggerate the vertical scale, the multiplying factor should be limited to avoid conveying a misleading impression. Where the ground information is either very variable or too sparse to enable cross sections to be prepared, individual borehole logs plotted diagrammatically are an acceptable alternative. If it is particularly important to prepare cross sections, sparse and variable information can sometimes be supplemented by means of information from soundings and geophysical investigations on areas between boreholes. It can be helpful to

19


indicate relevant soil parameters on cross sections, for example, results of standard penetration tests, triaxial tests and representative parameters from consolidation tests.

3.1.2 Interpretation of Lab and In-Situ Test Results

3.1.2.1 Laboratory Test

Interpretation of laboratory testing results describes the outcome of laboratory testing performed for the projects. Laboratory testing is necessary to help establish specific characteristics and engineering properties of the subsurface materials encountered. Such parameters are subsequently used in engineering analyses to evaluate embankment slope stabilities; estimate settlements of fills and foundation elements; determine allowable bearing capacities for the soil and/ or bedrock encountered at a site; and provide construction monitoring criteria such as soil moisture-density relationships and fill compaction requirements. These tests are commonly used in the development of geotechnical recommendations.

1. Laboratory Determination of Moisture Contents of Soils

These are the tests to determine the percent of moisture in a soil relative to the soil’s dry unit weight The results of this testing may be compared to moisture-density relationships to determine if in-situ water contents are above or below a soil’s optimum moisture content. This comparison may help identify if a soil will require the addition of water, or if it will need to be dried, during construction when it is used as fill material. Review of moisture contents may also provide an indication of the presence of groundwater, seepage, very wet or dry soils, etc.

2. Particle Size Analysis of Soils

These tests are used in determining the engineering classification of a soil. This battery of tests also provides specific data regarding grain sizes of a soil. Estimation of specific grain sizes may be necessary for subsequent engineering analyses.

3. Specific Gravity of Soils

Specific gravity is a relationship between the unit weight of water and the unit weight of the soil. It can be used to estimate void ratio when a soil’s unit weight and water content are known.

4. Atterberg Limits

Atterberg limits are water contents at which the engineering behavior of a soil changes. These test results help provide a qualitative indication of a soil’s tendency to shrink or swell with changes in moisture contents. Atterberg limits are commonly used to establish engineering classifications of soils.

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5. Moisture – Density Test (Standard Proctor Method)

This procedure determines relationships between water contents and dry unit weights of a soil sample for which 70 percent or more, by weight, of the sample passes a ¾ - inch sieve. It establishes a soil’s maximum dry density and optimum moisture content. The results of this test are used to develop soil compaction criteria, and help determine percent compaction of fill during construction activities.

6. Moisture – Density Test (Modified Proctor Method)

This procedure also determines relationships between moisture contents and dry weights of a soil sample for which over 30 percent, by weight, of the sample is retained on a ¾ - inch sieve.

7. Compression Test

The compression test determines the strength of a soil sample under various stress conditions. The compression test may be broken down into the three major categories used by the department:-

a. Unconfined Compression Test

This test is commonly used on soil and rock samples. It does not realistically model the strength of the in-situ soil, which exists under significant confinement. This test is used on rock samples to evaluate the strength and hardness of the rock for tunneling or other excavation projects. Use the test with caution for design purposes since it usually under estimates in-situ material strength properties.

b. Confined Compression Test (UU Triaxial)

This test more accurately evaluates the strength of the in-situ than the unconfined compression test. It is often referred to as an unconsolidated undrained (UU) test.

c. Consolidated Undrained Test (CU Triaxial)

This test is used to evaluate the long – term (drained) soil strength parameters which occur over periods of months to years when the equilibrium of pore water pressures in response to load has time to take place. As the sample is tested, the pore water pressure is measured in order to adjust the strength data for the effects of pore water pressure. By removing the pore water effects, the drained soil parameters are determined.

8. Consolidation Test

From this data, the compressibility of a sample and compression rate are determined for estimating settlement in the field. Due to the variable nature of soils in the field, the settlements predicted from this test are often higher than settlements observed in the field.

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3.1.2.2 In-Situ Test Interpretation of in–situ testing results describe the outcome of various tests that may

be conducted as supplementary to a ground investigation carried out by boreholes. The engineering properties of the soils can be assessed by means of a range of in–situ or laboratory tests. Methods of in-situ testing commonly used include:-

1. Standard Penetration Test

The Standard Penetration Test, which is carried out during drilling, records the number of blows (N) that are required to drive a standard sampler a distance of 300 mm below the base of the borehole. Blow count provides an indication of the relative strength of the soils encountered. The sampler is initially driven 150 mm to penetrate through any disturbed material at the bottom of the borehole before the test is carried out. The number of blows required for each 75 mm advance in the initial seating drive should be recorded; the test may then proceed, with recording of the number of blows required for each 75 mm incremental advance of the test drive.

When the test is used in soils derived from in – situ rock weathering, it should be noted that the empirical relationships developed for transported soils between N value and foundation design parameters, relative density and shear strength may not be valid. Corestone, for example, can be responsible for misleadingly high values that are unrepresentative of the mass. In view of this, the test should only be used to give a rough indication of relative strength in these soils, or to develop site – specific correlations.

2. Vane Shear Test

The Vane Shear Test measures the torque required to rotate a calibrated vane in the sediments, from which the measured torque value can be related to the shear strength of the soil. This test is very useful for determining the in–situ undrained strength of the marine mud and clayer alluvial deposits. However, if the sediments are sandy or contain shells, the vane shear results should be interpreted with caution. In addition, there exist strong evidence that in – situ vane shear tests (e.g. Clause 4.4 of BS 1377: Part 9:1990) give values too large for design. The use of proper reduction factor for the in–situ vane shear strength as proposed by Bjerrum (1972), Ladd et al (1977) and Aas et al (1986) should be noted.

3. Static Probing or Cone Penetration Test

The Static Cone Penetration Test generally provides a rapid means of determining the soil type, the soil profile, and the soil strength by measuring the resistance encountered by the tip of the penetrating cone. This test is also used as a rapid and economical means of interpolating between boreholes. Although it may be possible to estimate the type of soil through which the cone is passing but it preferable to carry out the test in conjunction with other means of determining the nature of the soil.

22


Several types of static probing equipment have been developed and are in use throughout the world (De Ruiter, 1982; Sanglerat, 1972). The basic principles of all systems are similar, in that a rod is pushed into the ground and the resistance on the tip (cone resistance) is measured by a mechanical, electrical or hydraulic system. There is no British Standard for cone penetration testing, but suitable recommendations are given by the ISSMFE (1977) and the ASTM (1985). Both of these test standards recognize a number of traditional types of penetrometers, and it imperative that the actual type of instrument used is fully documented, as the interpretation of the results depends on the equipment used.

The recently developed “piezocone”, which incorporates a pore pressure transducer within an electrical cone, has also found application in some marine investigation (Blacker & Seaman, 1985 et al, 1984; Koutsoftas et al, 1987).

Results are normally presented graphically with cone resistance (and local skin friction where a friction jacket cone is used) plotted against depth. The friction ratio, defined as (friction resistance/ cone resistance) x 100, may also be plotted against depth. This ratio is used to assist in interpreting the soil type penetrated. Suitable scales for plotting the results are given in ISSMFE (1977).

4. In–Situ Direct Shear Test

The test is generally designed to measure the peak shear strength of the intact material, or of a discontinuity (including a relict joint in soil), as a function of the normal stress acting on the shear plane. More than one test is generally required to obtain representative design parameters. Graphs of consolidation behaviour (if applicable) and shear force (or stress) plotted against both normal and shear displacements are prepared in the analysis. The peak shear stress and corresponding shear and normal displacements may then be obtained and related to the applied normal stress. When failure occurs in a plane dipping at an angle to the applied shearing force, this should be accounted for in the analysis (Bishop & Little, 1967). For tests on discontinuities in rock, the results from individual tests should not be extrapolated to the rock mass without confirmation that the surface tested is representative of the overall roughness of the discontinuity.

Table 3.1 lists the in–situ and laboratory tests that can be carried out during marine

ground investigations, together with the type of information provided by the tests. Additional tests such as particle size distribution, Atterberg limits, moisture contents and soil density tests are usually requested to provide information on the general properties of the soils, correlation between soils in different locations, and further details to support the geotechnical parameters. For silty or clayer soil, information on the undrained shear strength is necessary to assess the stability of marine structure such as gravity or sloping seawalls.

23


Table 3.1: lists the in – situ and laboratory tests

Tests Soil Tested Information Revealed

Field tests:

Vane shear test • Silty/ clayer deposit • Undrained shear strength Static cone penetration test

• Silty/ clayer deposit • Sandy deposit • Highly or completely

decomposed bedrock, residual soil

• Generally not suitable for gravel and stiff clays

• Soil profile • Interpretation of soil type from cone

resistance and friction with reasonable accuracy

• Strength indication • Interpolation of information

between boreholes Standard penetration test

• Sandy deposit • Highly or completely


• Soil type and profile • Strength indication

Laboratory tests :

Unconsolidated undrained triaxial compression test

• Silty/ clayer deposit • Undrained shear strength

Consolidated drained/ undrained triaxial compression tests

• Silty/ clayer deposit • Sandy deposit • Highly or completely


• Effective shear strength parameters

Direct shear test • Cohesive and cohesiveless soils

• Shear strength parameters

One-dimensional consolidation test (Oedometer test)

• Silty/ clayer deposit • Coefficient of consolidation • Coefficient of volume

compressibility • Coefficient of secondary

compression • Preconsolidation pressure

Isotropic compression test

• Soil of sedimentary origin containing laminations of sand and silt

• Highly or completely decomposed bedrock, residual soil

• Coefficient of consolidation • Coefficient of volume

compressibility • Preconsolidation pressure

Heavy metal, organic and biological tests

• Soils down to the base of the layer to be dredged

• Sediment classification according to WBTC 3/2000

• Depth of contamination

Note : 1. The coefficient of horizontal consolidation of silty/clayer deposit may also be determined from the Rowe Cell Consolidation Test. Reference on the test can be made to : (a) Head (1985) – Manual of Soil Laboratory Testing Volume 3 : Effective Stress Tests, pp 1129 – 1225; and (b) GEO (1996) – Conventional and CRS Rowe Cell Consolidation Test on Some Hong Kong Clays, GEO Report No. 55. 2. WBTC 3/ 2000 – Works Bureau Technical Circular 3/ 2000: Management of Dredged/ Excavated Sediment.

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It should be emphasized that the specified laboratory testing conditions should resemble, as closely as possible, the field conditions in which the works or structures will be constructed and operate under various stages. The initial state of the samples as well as the state of the soils in the construction and operation conditions should be clearly specified. Adequate number of samples should also be tested under different stress conditions in order to determine the shear strength and settlement parameters of the soils at different locations and depths. 3.1.3 Description of Soil/ Rock Properties

The properties of soil and rock must be accurately evaluated in order to produce safe and economical designs.

3.1.3.1 Engineering Properties of Soils

Engineering properties of soils are determined by:-

• Parent materials • Mineralogical composition • Organic matter content • Age • Method of transportation • Place of deposition • Method and degree of compaction • Texture • Gradation • Structure

Consequently, it is advantageous to classify soils and rocks into groups that exhibit

distinct engineering properties. This enables engineers in preliminary investigations as well as in design and construction to exchange:

• Reliable information • Experience • Data

To the engineer engaged in the design and construction of any structures, some of the

important physical and engineering properties of soils are:

• Permeability • Elasticity • Plasticity • Cohesion

25


• Angle of internal friction (φ) • Moisture content • Density • Shrink/ swell potential • Compressibility • Grain size distribution

The subsections below discuss these properties.

1. Permeability

Permeability is a property indicating the ease with which water flows or passes through a material. This water movement is called percolation. The knowledge and extent of this condition is especially important in the design and construction of underground excavations. Soil texture, gradation, degree of compaction, and primary structure strongly influence the relative permeability of soil. Generally, coarse – grained soils are much more permeable than fine – grained soils, although this is easily altered by presence of fines or cementing agents, openings, etc.

2. Elasticity

Elasticity is property indicating the ability of a material to return to its original shape or form after having been deformed by a load for a short period of time. Any load applied that exceeds the shear strength of a soil will also exceed the elastic limit of the soil, and it will not return to it original shape or form but will fail by plastic deformation. When a soil is disturbed by pile driving, the elastic limit of the soil must be exceeded to advance the pile. For this reason, the soil structure and properties in the vicinity of a pile may be radically changed.

3. Plasticity

Plasticity is a property indicating the ability of a material to be deformed permanently without cracking or crumbling.

4. Cohesion

Cohesion is a very important property contributing to the shear strength of a soil, and is the capacity to resist shearing stresses as indicated by Coulumb’s equation, c + wh (tan N). Cohesion varies depending on water content, density, and plasticity of the soil.

5. Angle of Internal Friction (φ)

The angle of internal friction is a measure of the natural angle of repose of a soil. For dry sand, this is the angle of approximately 30 degrees observed on the side slopes of a stockpile. For a clayer or clay soil, this is not the case since negative pore pressures generated by the low permeability of the soil matrix

26


masks the expression of the frictional properties of the soil. Moderate to high plasticity clays exhibit a typical friction angle of approximately 15 degrees when pore pressures reach equilibrium.

The angle of internal friction is also the slope of the shear strength envelope, and therefore, represents the effect that increasing effective normal stress has on the shear strength of the soil.

6. Moisture Content

Moisture content is the ratio of the weight of water to the weight of solids in a given volume of soil. Moisture contents can range from a few percent for rocks to several hundred percent for very soft highly organic coastal clays. The consistency of clay may be very soft or very hard depending upon the water content. Between these extremes, the clay may be molded and formed without cracking or rupturing the soil mass.

7. Density

Dry density is the unit weight of the solid particles of soil or rock per unit volume. Wet density is the unit weight of the solid particles and the natural moisture and is used in computations for determining design values for foundations above the water table. Submerged density is wet density less the unit weight of water and is used when the foundation is below the water table. Typical values for wet density of soils range from 1920 to 2160 kilograms per cubic meter.

8. Shrink/ Swell Potential

Shrinking/ swelling is a property of fine – grained soils, especially clays, resulting from build – up and release of capillary tensile stresses within the soil’s pore water and the varying degree of affinity for water that certain clay minerals exhibit. If founding in this type of material cannot be avoided, measures should be taken to reduce adverse effects upon the structure. Differential movement can be minimized by placing all footings with approximately equal bearing pressures within the same material.

9. Compressibility

Compressibility is property greatly influenced by soil structure and the load history of the deposit. Drilled shafts or footings should not bear in a material that is susceptible to a high degree of compression (consolidation). Negative friction, in which the soil pulls down (down – drag) on the shaft or piling instead of supporting load, often occurs in regions of incompletely consolidated soft clay, silt and organic soil, but may also be the result of soils shrinking during extended dry periods. The best solution is to found in a material below the point of possible moisture fluctuation, deep enough to cancel out any negative skin friction. It is also recommended that all

27


foundations for a particular structure element, such as bridge abutment, be founded at roughly the same elevation.

10. Grain Size Distribution

The next paragraphs discuss

• Soil permeability • Soil compatibility • Grain size distribution chart

a. Soil Permeability

The grain size distribution or range of particle sizes in a sample influence several soil properties. One of these properties is the permeability of the soil. A granular soil with a wide range of grain sizes (Well Graded) especially in the finer ranges will be less permeable than a granular soil with most of the particle sizes within a narrow range. As a result, soils with low permeability drain much slower, which in turn may lead to difficulties in obtaining proper compaction in the field.

b. Soil Compatibility

While the compatibility is indirectly influenced by permeability, it is also directly influenced by grain size distribution. Soils consisting solely of particles within a narrow size range (Uniformly or Poorly Graded) may be difficult to compact due the lack of other particles to interlock with the predominate particle size. The result is that density is difficult to achieve at the surface of the soil.

c. Grain Size Distribution Chart

Figure 3.1 is a grain size distribution chart showing some typical gradations. Well graded refers to the size of the particles being distributed over a wide range of sizes. Uniformly graded refers to the size of particles being distributed over a narrow range of sizes. Gap graded refers to several distinct size ranges within a sample.

3.1.3.2 Engineering Properties of Rocks

When rock is exposed to the weathering process, the rock is ultimately broken down by physical and chemical agents into loose, unconsolidated material or soil. Therefore, the physical properties of a rock depend to a large extend upon the degree of weathering. If the rock is fresh or unweathered, the typical properties are affected by:

• Constituent minerals • Degree to which the grains are bound together • Size and arrangement of the grains which produce such structures as banding and

foliation • Degree of fracture, jointing and bedding of the rock mass

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Fig. 3.1: Typical Particle size gradations (grain size distribution chart)

For igneous rocks, the physical properties are the least variable, excluding the effects

of fracturing. Sedimentary rocks, on the other hand, are so variable that it is difficult to characterize their physical properties. Consequently, each deposit must be evaluated individually. Some of the important engineering properties of rocks are:

• Density • Strength and hardness • Durability • Joints and faults

The next subsections cover these engineering properties.

1. Density

The strength of rock is in direct proportion to its crystalline makeup and compaction or cementation. In general, the strongest rocks are the densest. However, rock with ferrous constituents may have a high density and low strength.

2. Strength and Hardness

These properties are a relationship between various physical constituents that make up an individual rock. Some of these physical properties are:

• Density • Bonding • Cementation

29


The strongest rocks are, in general, igneous or metamorphic in origin. Sedimentary rocks are variable and range from hard to the very soft.

3. Durability

A rock’s physical and chemical characteristics determine its durability. The crystalline igneous and metamorphic rocks (such as granite, basalt, quartzite and gneiss) are the most durable. Sedimentary rock, which is the least durable, is greatly affected by weathering; a typical example is limestone or sandstone with carbonate cement.

4. Joints and Faults

The next paragraphs cover:

• Joint description • Fault description • Cut stability

a. Joint Description

Joints are fractures in rock resulting from previous stresses to which the rock mass has been subjected. Joints are normally nearly vertical, but they may occur at almost any orientation. Joints differ from faults in that little or no displacement is present along the joint. Joints typically occur at fairly regular intervals in a rock mass.

b. Fault Description

Faults are breaks in rock where movement has occurred. The movement can range from a few inches (50 mm) to hundreds of feet (meters). Faults with large displacements typically have a zone of fractured and weathered rock on each side of the fault that is unstable and behaves more like soil than rock. They are normally not vertical but inclined at an angle.

c. Cut Stability

Joints and faults impact the stability of cuts in rock. Since these features divide the rock mass into discrete pieces, the pieces may fall out of the cut face. If these features are inclined downward into a cut, large masses of rock can fail unexpectedly into a cut with little warning. If these conditions occur, rock bolting or nailing to stabilize the face should be considered.

3.1.4 Selection of Geotechnical Parameters

The data on which the analysis and recommendations are based should be clearly indicated. The information generally comes under two separate headings:

30


1. Information related to the project (which is usually supplied by the designer). For

example, for buildings and other structures this should include full details on the loading (including dead and live loads), column spacing (where appropriate), depth and extent of basements and details of neighbouring structures. For earthworks, the height of embankments, the materials to be used and the depths of cut slopes are relevant to the interpretation.

2. Geotechnical Parameters (which are usually selected from the descriptive report by the

engineer who performs the analysis and prepares the recommendations). There is no universally accepted method of selecting these parameters, but the following approach may help to arrive at reliable values:

a. Compare both laboratory and in – situ test results with ground descriptions b. Cross – check, where possible, laboratory and in – situ results in the same

ground c. Collect individually acceptable results for each ground unit, and decide

representative values appropriate to the number of results

3. Where possible, compare the representative values with published data for similar geological formations or ground units.

3.2 RECOMMENDATIONS ON GEOTECHNICAL DESIGN

The following list, which is by no means exhaustive, indicates the topics on which advice and recommendations are often required, and also what should be included in the report.

3.2.1 Slope stability

Geological model; shear strength parameters; water pressures for the design condition; assessment of risk to life and economic risk; recommended slope angle. Comment should be made on surface drainage and protection measures, and on any subsurface drainage required. For rock slopes, an assessment on potential failures due to unfavourably orientated discontinuities should be made. Possible methods of stabilizing local areas of instability and surface protection measures should be recommended. Advice on monitoring of potentially unstable slopes should also be given (GCO, 1984).

31


3.2.2 Retaining Walls

Earth and water pressures; passive and frictional resistance; foundation bearing capacity, see Geoguide 1 (GCO, 1982).

3.2.3 Embankment

Stability of embankment foundations; assessment of amount and rate of settlement and the possibility of hastening it by such means as vertical drains; recommendations for side slopes (see 3.1 above); choice of construction materials and methods.

3.2.4 Drainage

Possible drainage methods during construction for works above and below ground;

general permanent land drainage schemes for extensive areas. 3.2.5 Basement

Earth and water pressures on basement walls and floor; comment on the possibility of floatation. An estimate of the rise of the basement floor during construction should be made, where appropriate.

3.2.6 Piles

Types of piles suited to the ground profile and environment; estimated safe working loads, or data from which they can be assessed; estimated settlements of structures.

3.2.7 Ground anchors Bearing ground layer and estimated safe loads, or data from which they may be calculated, e.g. suitability tests (Brian – Boys & Howells, 1984).

32


3.2.8 Tunnels and underground works Methods and sequence of excavation; weather excavation is likely to be stable without support; suggested methods of lining in unstable excavations; possible use of rock bolting; possibility of encountering groundwater, and recommendations for dealing with it; special features for pressure tunnels.

3.2.9 Safety of neighbouring structures Likely amount of movement caused by adjacent excavations and ground water lowering, compressed air working, grouting and ground freezing or other geotechnical processes. The possibility of movement due to increased loading on adjacent ground may also need to be considered.

3.2.10 Monitoring of movements

Need for measuring the amount of movement taking place in structures and slopes, together with recommendations on the method to be used; recommendations for taking photographs before the commencement of works.

3.2.11 Chemical attack

Protection of buried steel or concrete against attack from aggressive soils and groundwater.

33

Maritime Unit Geotechnical Analysis

CHAPTER 4

GEOTECHNICAL ANALYSIS 4.0 INTRODUCTION

An engineering analysis combines the information obtained from the geotechnical field investigation and the laboratory test results to determine the engineering properties and drainage characteristics of the subsurface materials. In addition, the analysis should alert designers, contractors, and construction personnel of potential problems and provide economical solutions with consideration given to alternatives. Finally, the analysis should provide an assessment of risk associated with each of the possible solutions. This chapter does not give detailed textbook solutions to engineering problems but will provide general guidelines, potential pitfalls of these guides, and specific references to assist the engineer in performing a detailed analysis.

The quality of the analysis depends on several factors. Knowledge of engineering

principles and practical experience in application of these principles is of course very important; but a thorough analysis cannot be accomplished without a clear understanding of the proposal details. This understanding requires a flow of communication and information between Project Development, Structure Design, Planning and Coordination, and the geotechnical engineer. To provide an acceptable analysis of geotechnical information that is practical, economical, and of sufficient detail, completed information of the project is necessary. The project development process must provide for this information to be obtained and must incorporate sufficient time to allow proper investigation and analysis.

As a minimum, the geotechnical analysis should result in a subsurface profile with

design soil strength parameters and an engineering evaluation of the subsurface conditions. 4.1 STABILITY ANALYSIS 4.1.1 General

This section presents methods of analyzing stability of natural slopes and safety of embankments. Diagrams are included for stability analysis, and procedures for slope stabilization are discussed.

34


4.1.2 Methods of Analysis

Various techniques of slope stability analysis may be classified into three broad categories:-

1. Limit Equilibrium Method

• Most of the methods of stability analysis currently in use fall in this category.

2. Limit Analysis Method 3. Finite Element Method

4.1.3 Required Safety Factors

The following values of safety factors should be provided for reasonable assurance of stability:-

1. Safety factor no less than 1.5 for permanent or sustained loading conditions. 2. For foundations of structures, a safety factor no less than 2.0 is desirable to limit

critical movements at foundation edge.

3. For temporary loading conditions or where stability reaches a minimum during construction, safety factor may be reduced to 1.3 or 1.25 if controls are maintained on load application.

4. For transient loads, such as earthquake, safety factors as low as 1.2 or 1.5 may be

tolerated. 4.1.4 Effects of Soil Parameters and Groundwater On Stability

Soil strength parameters are selected either on the basis of total stress, ignoring the effect of the pore water pressure, or on the basis of effective stress where the analysis of the slope requires that the pore water pressures be treated separately.

The choice between total stress and effective stress parameters is governed by the drainage conditions which occur within the sliding mass and along its boundaries. Drainage is dependent upon soil permeability, boundary conditions, and time.

35


1. Total Stress Analysis

Use the undrained shear strength parameters such as vane shear, unconfined compression, and unconsolidated undrained (UU or Q) triaxial compression tests. Field vane shear and cone penetration tets may be used. Assume ∅ = 0.

2. Effective Stress Analysis

The effective shear strength parameters C’ and ∅’ from CD tests, CU tests etc. should be used.

Subsurface water movement and associated seepage pressures are the most frequent cause of slope instability. Therefore, should seepage pressures, construction pore pressures, excess pore pressures in embankment foundations or artesian pressures be found to exist, they must be used to determined effective stresses and unit weights, and the slope and foundation stability should be evaluated by effective stress methods.

4.1.5 Slope Stabilization

During the planning and design stage, if analyses indicate potential slope instability, means for slope stabilization or retention should be considered. This section will discussed some of the methods used for slope stabilization purposes.

1. Geomatrical Control

a. Cut Slope

i. All untreated slopes shall be designed to 1:1 to 1:1.5 with 2 m berm for cut slopes in residual soils and in completely decomposed rock.

ii. Maximum height of slopes shall limited to 6 m with Factor of safety greater than 1.30

iii. The minimum Factor of safety for treated slopes shall be 1.50 iv. Generally the maximum number of berms in a cut slope is restricted to

six (6) berms unless there is difficulty to construct it due to the terrain encountered.

b. Fill Slopes and Embankments

i. Fill slopes and embankments shall be constructed to a gradient of 1:1.5 to 1:1.2 with 2 m berm width.

ii. Maximum height of slopes shall limited to 6 m height with a Factor of Safety greater than 1.25

iii. Minimum Factor of Safety for treated slopes shall be 1.50 iv. For steeper slopes, stabilization measures shall be provided such as

geogrid/ geotextiles reinforcement, retaining structure, reinforced fill structure etc.

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See Table 4.1 and Table 4.2 for some typical slope construction criteria.

Table 4.1: Typical Slope Construction (No. of Berms)

No. of Berms Typical Construction

< 3 Normal slopes 1:1.5 to 1:2 (Vertical:Horizontal)

> 3 Reinforced slopes 4:1 (Vertical:Horizontal) Side – Long Fill

on Slope > 6 Replace with retaining structure

< 6 Normal slope 1:1.5 to 1:2 (Vertical:Horizontal)

> 6 Reinforced slope 4:1 (Vertical:Horizontal) Embankments

> 6 Replace with elevated structure

< 6 Normal slopes 1:1 with surface drains and 2.0 m berms Cut slopes

> 6 Soil nailing with slope gradient 4:1 to reduce no of berms

Table 4.2: Typical Slope Construction (Slope angle)

Slope Angle Typical Construction

≤ 35° Normal slopes 1:1.5 to 1:2 (Vertical:Horinzontal)

≤ 35° Reinforced slopes 4:1 (Vertical:Horizontal) Side – long fill on

slope ≥ 35° Replace with retaining structure

≤ 35° Normal slopes 1:1.5 to 1:2 (Vertical:Horinzontal)

≥ 35° Reinforced slopes 4:1 (Vertical:Horizontal)

Embankments

≥ 35° Replace with elevated structure

2. Earth Berm Fill

a. Compacted earth or rock berm placed at and beyond the toe. b. Drainage may provided behind berm c. Sufficient width and thickness of berm required with Factor of Safety greater

than 1.50 to ensure that failure will not occur below or through berm

Earth berm fill

37


3. Geogrid/ Geotextiles Reinforcement

Generally, in construction industry there are four primary uses for geotextiles: separation, drainage, filtration and reinforcement. Due to the very wide range of applications and the tremendous variety of available to the geotextiles, the selection of a particular design method, or design philosophy, is a critical decision and the ultimate decision for a particular application can take one of three directions :-

a. Design by cost and availability

i. The method is obviously very weak technically ii. Design procedure :-

o Take the fund available divided by area to be covered o Calculates a maximum allowable geotextiles unit price. o The fabric (assuming it is available) is then selected within this

price limit.

b. Design by specification

i. The method is a normal practice and is used almost exclusively by JKR.

ii. Specifications of woven geotextile are as follows. The properties of high strength woven geotextile reinforcement are tabulated below in Table 4.3.

o Reinforcement geotextiles shall be of high modulus woven polyster geotextile.

o Joint :- Warp Joint (Reinforcing Direction)

No joint shall be allowed in the reinforcing direction laid across the embankment. If any joint shall be performed to reduce wastages. It shall be conducted using a 600N breaking load aramide thread (yellow) at not less than 3 stitches per 25mm with a double chain stitch sewing machine. Seams shall be tested using ASTM D4884 or other approved test standard.

Weft joint (Parallel to the strip length of the geotextile) Joint shall be performed in the weft joint using polyster or aramide thread of breaking load not less than 250N at not less than 3 stitches per 25mm with a double stitch sewing machine.

o Approval :- Only locally produced geotextiles accredited with ISO

9002 certification complying with the specification shall be used.

Catalogue and samples shall be submitted for the prior written approval of the S.O before the procurement of geotextile.

o Placement sequencing of fill over geotextile to be to the approval of the S.O before execution.

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iii. Specifications of non-woven geotextile for separator/ filters are as follows. The properties of non-woven geotextile are tabulated below in Table 4.4.

o All geotextile shall be from an approved local manufacturer and shall be accredited with ISO 9002 testification manufactured from polypropylene or equivalent geotextile shall be durable and resistant to naturally occurring chemical, fungi and bacteria when installed in contact with the materials to be separated. Geotextiles shall be free of any flaws which may have adverse effects on the physical and mechanical properties of the geotextiles.

o Geotextile fabrics shall be non – woven needle punched or spun bonded or thermally bonded or chemically geotextiled in accordance with the specifications and shall be used as shown and described in the drawings.

o Geotextiles shall be stabilized against ultra – violet radiation to the degree that one month’s exposure of the geotextiled to sunlight shall not reduce its strength to less than 90% of the specified strength rating in the specification.

o The type of geotextile fabrics as shown on the drawings shall comply with the properties as listed in the table.

o Placement sequencing of fill over geotextile to be to the approval of the S.O before execution.

c. Design by function

i. The individual steps in this process are as follows :- o Assess the particular application considering not only the

geotextile but the material system on both sides of it. o Depending on the criticality of the situation (“ If it fails, what are

the consequences?”), decide on a minimum factor of safety. o Decide on the geotextile’s primary function. o Calculate numerically the required fabric property value in

question on the basis of its primary function. o Test for or otherwise obtain the candidate geotextile’s allowable

value of this particular property. o Calculate the actual factor of safety on the basis of the allowable

property divided by required property for the actual factor of safety.

Property RequiredProperty Allowable

=FS

Where;

Allowable Property = a value based on a laboratory test that models the actual situation.

Required Property = a value based on a design method that models the actual situation.

o Compare this factor of safety to the required minimum value

decided on in early step.

39


o If not acceptable, check into fabrics with more appropriate properties.

o If acceptable, check if any other function of the geotextile is more critical.

o When sufficient fabrics (that are available) are found that satisfy the minimum requirement, select the fabric on the basis of least cost.

4. Retaining Structures

The ability of retaining structures to perform as a stabilizing mass is a function of how well it will resist overturning moments, sliding forces at or below its base, and internal shear forces and bending stresses. The design strength and serviceability limits of structural materials should be as recommended in the appropriate structural codes of practice such as BS 8110 : Part 1 and Part 2, BS 5400 : Part 3 and Part 4, BS 5950 : Part 1 and BS 5628 : Part 1, Part 2 and Part 3.Some retaining structure types include :-

a. Conventional Gravity or Cantilever Walls

i. The design of retaining wall should be such that the wall as a whole must satisfy the basic design criteria summarized below in Table 4.5.

ii. Structural design :- o Normally mass concrete walls should be design on a no – tension

basis under the design earth pressures. o Grade 15 concrete or stronger is used and construction joints are

prepared in accordance with BS 8110 : Part 1 and Part 2 or BS 5400 : Part 1 and Part 4 to transfer tensile or shear stress then permissible stresses of 0.28 N/mm2 in tension and 0.55 N/mm2 in shear may be used.

iii. Certain other important points, which should be kept in mind in designing the retaining walls, are :-

o Walls should be provided with weep holes at regular intervals. o Clay backfills should preferably be avoided, because climatic

change likely to cause successive swelling and shrinkage of the backfill soil. Swelling causes unpredictable pressure on the wall; and the subsequent shrinkage may cause formation of cracks in the soil surface.

o A filter of a course permeable material should preferably be laid behind the wall before filling the backfill. This would help in preventing the development of high pore pressures within the backfill, as the water getting into the backfill will percolate through the filter and get out of the weep holes, without clogging the weep holes.

o When a wall is founded on a compressible soil such as fully saturated clay, then the non – uniform base pressure will result in the progressive tilting of the wall due to consolidation of the soil. Hence, a wall constructed on compressible soil should be so dimensioned that the resultant R acts close to the mid points of its base.

40


41

b. Embedded or Sheet Walls

i. Piles may be of timber, concrete or steel and may have lapped, V – shaped, tongued and grooved or interlocking joints between adjacent piles. The typical design criteria for piles as retaining structures are tabulated below in Table 4.6.

1. Steel Sheet Piling

o A comparatively small displacement of soil is caused during driving and suitable sections can be driven into almost any soil except strong rocks.

o Reference should be made to grade 5275P for the properties of mild steel and grade 5355P for high yield steel to BS EN 10025: 19904).

o Where steel sheet piling is manufactured to other standards, care should be taken that the design stresses to be used are compatible with that particular quality of steel.

o The structural design should be in accordance with BS 449: Part 2.

o The calculations should consider the bending stresses and corrosion at several levels to determine the section of piling needed.

o The stresses which will be imposed on the piles during driving should be considered when the sheet pile wall is being designed.

2. Timber Sheet Piles

o May be used for walls of moderate height, in river and sea

defense works and in wharf construction. o Timber sheet piling may be an economic material but the

joints are not as watertight as steel sheet piling. o Types of timber :-

Certain softwoods and hardwoods are suitable as permanent sheet piling.

The choice will depend upon availability in suitable sizes, appropriate preservation treatment, the expected service life and the relative cost.

o Quality of timber :- Pressure – treated timber piles shall conform to MS 822

and shall be approved by SIRIM. o Design :-

Working stresses should not exceed the green permissible stresses given in BS 5268: Part 2 for the species and grade of timber being used.

In calculating the stresses, account should be taken of the stresses during installation and in use.

Allowance should be made for reduction in section by drilling or notching.


Table 4.3: Properties of High Strength Woven Geotextile Reinforcement (Nota Teknik 20/98)

Item Description Properties Test Standard

1.0 Type (Or Equivalent) HS 100/50

HS 150/50

HS 200/50

HS 300/50

HS 400/50

HS 600/50

HS 800/50

2.0 Form Woven Polyster

Woven Polyster

Woven Polyster

Woven Polyster

Woven Polyster

Woven Polyster

Woven Polyster

3.0 Ultimate Tensile Strength kN/m (WARP)

> 100 kN/m

> 150 kN/m

> 200 kN/m

> 300 kN/m

> 400 kN/m

> 800 kN/m

> 800 kN/m

ASTMD4595-86

Ultimate Tensile Strength kN/m (WEFT)

> 50 kN/m

> 150 kN/m

> 50 kN/m

> 50 kN/m

> 50 kN/m

> 50 kN/m

> 100 kN/m

ASTMD4595-86

4.0 Elongation At Ultimate Tensile Strength (WARP) < 10% < 10% < 10% < 10% < 10% < 10% < 10% ASTMD4595-

86

Elongation At Ultimate Tensile Strength (WEFT) < 12% < 12% < 12% < 12% < 12% < 12% < 12% ASTMD4595-

86

5.0 Creep At 50% of Ultimate Load After 2 Years < 1% < 1% < 1% < 1% < 1% < 1% < 1%

6.0 Minimum Unsewn Width of Geotextile 5.0m 5.0m 5.0m 5.0m 5.0m 5.0m 5.0m

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43

Table 4.4: Properties of Non-Woven Geotextile (Separator/ Filters) Type A. (Nota Teknik 20/98)

Item Description Test Method Unit Value1.0 Tensile Strength ASTM D4595-86 kN/m > 15 2.0 Elongation At Break ASTM D4595-/6 % > 40 3.0 Trapezodial Tear Strength ASTM D4533-91 N > 200 4.0 CBR Puncture Resistance DIN 54307 N > 2000 5.0 Mullen Burst ASTM D3786 kPa > 2850 6.0 Cone Drop BS 6906/6 mm > 20

7.0 Permeability At 100mm Head BS 6906/3 1/m2/s > 150

8.0 Aparent Pore Size 095 ASTM D4751-87 Micron > 150 9.0 UV Resistance ASTM D4355 % Retained 500 Hours > 70 10.0 Mass ASTM D5261-92 9/m2 > 230

Table 4.5: Design Criteria for Conventional Gravity and Cantilever Wall

Maximum Permissible Movement Design Component Mode of Failure Minimum FOS Design Life Vertical Lateral Differential

Over Turning 1.80 Sliding 1.60Overall Stability 1.50

Gravity and Cantilever Wall

Bearing 2.0

75 Yrs

15 mm along face of wall, Geoguide 1 (1983), GEO Hong Kong

15mm along face of wall

1 : 150 along face of wall


3. Reinforced and Prestressed Concrete Sheet Piles

o Reinforced Concrete Sheet Piles :- The design, manufacture and handling should be in

accordance with 7.4.2 of BS 8004: 1986. o Prestressed Concrete Sheet Piles :-

The requirements for materials, manufacture and driving of prestressed concrete piles should be as set out in BS 8110: Part 1 or BS 5400: Part 4, Part 7 and Part 8 and 7.4.3 of BS 8004: 1986.

In the design tensions up to a maximum of 50% of the modulus of rupture (in tension) may be permitted provided the ultimate strength requirements are satisfied. In this respect the guidance for class 2 structures in 4.3.4.3 of BS 8110: Part 1: 1986 is appropriate.

4. In – Situ Concrete Pile Walls

o Their best application is in cohesive soils, but the piles are

unsuitable where the ground water level on the retained side of the wall is high.

o Concrete and reinforcement should conform to the requirements of BS 8004, BS 8110: Part 1 or BS 5400: Part 4, Part 7 and Part 8.

o The mix should be designed to provide the necessary structural strength and the flow requirements to ensure adequate compaction and continuity.

5. Diaphragm Walls

o Diaphragm walls are cast or placed in the ground using a

bentonite or polymer suspension, as part of the construction process.

o For prestressed cast in – situ walls, Reference should be made to BS 8110 : Part 1 or BS 5400 : Part 4 for general recommendations of post – tensioned prestressed concrete design and construction.

o Precast diaphragm wall panels should conform to the recommendations of BS 8110: Part 1.

6. Soldier/ King Piles

o These consist of vertical members built at suitable centers

with a system of ground support spanning between them. o Sheet piles interlocking with H – section piles are also

commonly used. o This method is unsuitable for the exclusion of water and if

soil is washed out from behind the sheeting unacceptable settlement may be caused to adjacent structures or services.

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ii. Its also may be cantilever, anchored or propped structures.

1. Cantilever Retaining Walls

o Cantilever retaining walls are suitable for only moderate height.

o Maximum height is limited to 5m, but even this may be excessive where soft or loose soils occur in front of the wall.

o Stiffer cantilever walls, of concrete or steel including diaphragm walls and heavy composite walls, may be satisfactory to heights of 12m providing the ground is strong enough to give adequate support.

o It is preferable not to use cantilever walls when services or foundations are located wholly or partly within the active zone due to the deflections at the head of a cantilever wall are significant and horizontal/ vertical movement in the retained material may cause damage.

2. Anchored or Propped Walls

o Can be designed to have fixed or free earth support at the

bottom with the walls may have one or more levels of anchor or prop.

o Free earth condition :- The penetration of the piles should be designed so that

the passive pressure in front of the piles will resist the forward movement of the toes of the piles, but will not prevent rotation.

The piles are supported by ties at the top of the wall and the soil at the base of the wall, in a manner similar to a vertical beam with simple supports.

o Fixed earth condition :- Further penetration of the piles is required to ensure not

only that the passive pressures at the front of the wall resist forward movement but that the rotation of the toe is restrained by the development of passive pressures near the toe at the rear of the wall.

The provision of a simple support at the top due to the anchor or ties and a fixed support due to the soil at the base of the wall is similar to a vertical propped cantilever.

5. Others

Other potential procedures for stabilizing slopes include reinforced soil, gabions,

cribworks (timber or concrete) etc.

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46

4.2 SETTLEMENT ANALYSIS

4.2.1 General

Generally this section concerns:-

1. Settlement predictions and calculation of settlement times. 2. Design criteria for settlement analysis 3. Ground improvement methods of reducing or accelerating settlements.

4.2.2 Settlement Predictions and Calculation of Settlement Times.

Settlement is the direct result of reduction of volume of a soil mass. This reduction could be attributed to the following factors:-

• The escape of water and air from the voids • Compression of the soil particles • Compression of water and air within the voids

The total settlement of a stratum is generally regarded to be the result of a two phase

process:-

1. Immediate settlement

• Those that occur rapidly, perhaps within hours or days after the load is applied.

2. Consolidation Settlement

• It is a time – dependent deformation that occurs in saturated or partially saturated silts and/ or clays.

• These are soils that have low coefficients of permeability and are slow to dissipate the pore water.


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Table 4.6: Typical design Criteria for Pile as retaining Structure

Maximum Permissible Movement Design Component Mode of Failure Minimum FOS Design Life Vertical Lateral Differential

Tensile Resistance 2.0 Resistance at soil grout interface 3.0 Permanent Anchors

Creep/ corrosion

75 Yrs Geo Spec 1 (1989), GEO Hong Kong BS 8081

Individual foundation loads (mainly under lateral & bending loads perpendicular to axis of pile)

Ultimate Lateral Resistance 2.5 75 Yrs

12mm along axis of pile at pile head at design load (BS 8004)

12mm perpendicular to axis of pile at design load

Pile group Block Bearing Capacity 2.0 75 Yrs 12mm at working load (BS 8004)


It is common to further designate the consolidation as primary consolidation and secondary consolidation (or creep). Of the two, the primary consolidation is generally much larger. Secondary consolidation is speculated to be due to the plastic deformation of the soil as a result of some complex colloid – chemical processes whose roles in this regard are mostly hypothetical at this point. Also, the primary consolidation is easiest to predict, occurs at a faster rate than secondary consolidation, and is usually the more important of the two. In general, there are several methods for computation of settlement:-

Assume that;

∆H = Settlement from consolidation ∆e = Decrease in void ratio corresponding to a stress increase from Po to (Po + ∆P) at the mid – height of the layer Ht.

i. If ∆e is determined directly on the (e – Log P) curve from laboratory

consolidation test, ∆H is computed as follows :-

HtH

ee

o

∆=

+∆

1

)(1

HteeH

o+∆

=∆

ii. If compression index Cc is interpreted from a series of semi logarithmic (e – p)

curves of consolidation tests, ∆H is computed as follows :-

)(1 o

o

o PPP

Loge

CcHtH∆+

+=∆

iii. ∆H may be computed from av the slope of arithmetic (e – p) curves, in the range

from (Po) to (Po + ∆P) :-

o

v

ePHta

H+∆

=∆1

Where;

2

435.0PP

Ccao

v ∆+

=

For the purposes of computation of time rate of consolidation, the equation used is as

follows:-

U = Average percent of consolidation completed at any time t and depends on the degree of dissipation of the initial hydrostatic excess pore water pressure Uo.

48


U at any time is measured by the division of the area under the initial excess pressure diagram between effective stress and pore pressure:-

AuAA

UoHtAU

+==

σσσ

This relationship is evaluated by the theory of consolidation and is expressed by the

time factor Tv. To determine U as a function of time factor, use curves of Figure 9 (NAVFAC 7.1, MAY 1982, page 7.1 – 227)

2

.H

tCvTv =

H = Length of longest vertical path for drainage of pore water. For drainage to pervious layers at top and bottom of compressible stratum, H = Ht/2.

4.2.3 Design Criteria for Settlement Analysis

1. Embankment on Soft Ground

The settlement of the embankment will depend on the height of the embankment, the type and depth of the compressible strata and compressibility characteristics of the subsoil strata. The following criteria for settlement of the embankment will be adopted as JKR’s standard specification and guidelines:-

a. Total Settlement of embankment

• The settlement within the first five years of service shall not exceed 10 %

of the sum of the total theoretical primary consolidation settlement and secondary settlement, the latter being assessed for a period of 20 years.

• In addition, total post construction settlement shall no where exceed 400 mm.

b. Differential Settlements

• In areas of transition between piled approach embankments and general

low embankments, differential settlement within the first seven years of service shall not exceed 100 mm within a length of 50 m.

• In areas remote from structures and transition zones differential settlement shall not exceed 100 mm within a length of 100 m.

• Notwithstanding the allowable settlement of embankment, it will be ensured that services reallocations, particularly water mains, will not be adversely affected by post construction settlement.

49


c. Bearing Capacity • Minimum factor of safety against bearing capacity of embankment shall

be 1.40.

2. Tolerable Settlement for Building

a. Applications

For important structure, compute total settlement at a sufficient number of points to establish the overall settlement pattern. From this pattern, determine the maximum scope of the settlement profile or the greatest difference in settlement between adjacent foundation units.

b. Approximate Values

Because of natural variation of soil properties and uncertainty on the rigidity of structure and thus actual loads transmitted to foundation units, empirical relationships have been suggested to estimate the differential settlements (or angular distortion) in terms of settlement (see, Structure Soil Interaction, by Institution of Civil Engineers).Terzaghi and Peck (page 489) suggested that for footings on sand, differential settlement is unlikely to exceed 75 % of the total settlement. For clays, differential settlement may in some cases approach the total settlement.

c. Criteria

Differential settlements and associated rotations and tilt may cause structural damage and could impair the serviceability and function of a given structure. Under certain conditions, differential settlements could undermine the stability of the structure and cause structural failure. Table 4 (Allowable Settlements of Structures, by Bjerrum – NAVFAC 7.1, MAY 1982, page 7.1 - 239) provides some guidelines to evaluate the effect of settlement on most structures. Table 5 (NAVFAC 7.1, MAY 1982, page 7.1 - 240) provides guidelines for tanks and other facilities.

4.2.4 Ground Improvement Methods of Reducing or Accelerating Settlements

A lot of ground improvement methods have been used especially for construction of embankment on soft ground in order to reduce or accelerate settlement and dissipation of pore water pressure so that works can be completed much earlier than using conventional methods. Even if the embankment is stable, some form of settlement is expected to occur in the long term if the subsoil does not improve. Therefore, it may be necessary to adopt some form of ground treatment to minimize long term settlement, especially if the total and differential settlement is expected to be greater than the specified limits given in the specification.

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Some of the most common methods that are usually associated with construction of embankment on soft ground are:-

1. Preloading 2. Vertical Drains 3. Removal of Compressible Soils 4. Balancing Load by Excavation 5. Others

4.2.4.1 Preloading Preloading or surcharging is a method in which the load equivalent to or exceeding the

design load is applied to the ground and left until the required effects are attained then all or part of the applied load is removed to construct a main structure. This procedure causes a portion of the total settlement to occur before construction. It is used primarily for fill beneath paved areas or structures with comparatively light column loads. For heavier structures, a compacted fill of high rigidity may be required to reduce stresses in compressible foundation soil.

In addition to consideration of time available and cost, the surcharge load may induce shear failure of the soft foundation soil. Analyze stability of the embankment under surcharge by methods in 4.1.1 is required.

4.2.4.2 Vertical Drain Vertical drains are commonly used as a ground improvement method to dissipate pore

water pressure and accelerating the settlement of the ground allowing consolidation to take effect faster. Vertical drains accelerate consolidation by facilitating drainage of pore water but do not change total compression of the stratum subjected to a specific load.

Vertical drains can be used alone or as a combination with other methods such as preloading, vacuum preloading etc. Vertical drain is most suitable for predominantly fine grained, inorganic high water content and low strength soils and for normally consolidated or lightly over consolidated soil. Vertical drains are less effective in peat and organic soils, although some have been used successfully (Holtz et.al; 1990).

Vertical drains can be divided into two types (Mcgown and Hughes; 1985) :-

1. Round Drains

o Sand Drains o Sandwick Drains o Wrapped Flexible Pipe Drains

51


2. Band Drains

o There are many types of flat band drains e.g Kjellman, Mebra, Colbond, Geodrain, Alidrain etc in the market.

This section will not discuss into details for the function and the types of the Vertical

Drains. Concentration mostly directed to the Vertical Drain design and general design requirements of the methods used.

1. Vertical Drain Design

Normally triangular or square patterns are used at 1 – 4 m and 1.5 – 2.5 m spacing. Refer to Figure 20 (NAVFAC DM – 7.1, MAY 1982, page 7.1 – 250) for a trial selection of drain diameter and spacing, combine percent consolidation at a specific time from vertical drainage with percent consolidation for radial drainage to the drain. This combined percent consolidation Uc is plotted versus elapsed time for different drain spacing in the center panel of Figure 4.4. Selection of drain spacing depends on the percent consolidation required prior to start of structure, the time available for consolidation, and economic considerations. When a Vertical drain used as a combination with other methods such as preloading, vacuum preloading etc. The percent consolidation under the surcharge fill necessary to eliminate a specific amount of settlement under final load is determined as shown in the lowest panel of Figure 20 (NAVFAC DM – 7.1, MAY 1982, page 7.1 – 251)

2. General Design Requirements Analyze stability against foundation failure by the methods of section 4.1.1, including the effect of pore pressure on the failure plane. Determine allowable buildup of pore pressure in the compressible stratum as height of fill is increased.

a. Horizontal Drainage. For major installation investigate in detail the horizontal coefficient of consolidation by laboratory tests with drainage in the horizontal direction, or field permeability tests to determine horizontal permeability.

b. Consolidation Tests. Evaluate the importance of smear or disturbance by

consolidation tests on remolded samples. For sensitive soils and highly stratified soils, consider nondisplacement methods for forming drain holes.

c. Drainage Material. Determine drainage material and arrangement to handle

maximum flow of water squeezed from the compressible stratum in accordance with Chapter 6 (NAVFAC 7.1, MAY 1982, page 7.1 – 259)

4.2.4.3 Removal of Compressible Soils

Consider excavation or displacement of compressible materials for stabilization of fills

that must be placed over soft strata.

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1. Removal by Excavation

Organic swamp deposits with low shear strength and high compressibility should be removed by excavation and replaced by controlled fill. Frequently these organic soils are underlain by very loose fine sands or silt or soft clayey silts which may be adequate for the embankment foundation and not require replacement.

Topsoil is usually stripped prior to placement of fills; however, stripping me not be required for embankment higher than 6 feet as the settlement from the upper ½ foot of topsoil is generally small and takes place rapidly during construction period. However, if the topsoil is left in place, the overall stability of the embankment should be checked assuming a failure plane through the topsoil using the methods of section 4.1.1.

2. Displacement

Partial excavation may be accompanied by displacement of the soft foundation by the weight of fill. The advancing fill should have a steep front face. The displacement method is usually used for peat and mud deposits. This method has been used successfully in a few cases for soft soils up to 65 feet deep. Jetting in the fill and various blasting methods are used to facilitate displacement. Fibrous organic materials tend to resist displacement resulting in trapped pockets which may cause differential settlement.

4.2.4.4 Balancing Load by Excavation To decrease final settlement, the foundation of heavy structures may be placed above

compressible strata within an excavation that is carried to a depth at which the weight of overburden, removed partially or completely, balances the applied load.

1. Computation of Total Settlement

a. In this case, settlement is derived largely from recompression. The amount of

recompression is influenced by magnitude of heave and magnitude of swell in the unloading stage.

2. Effect of Dewatering

a. If drawdown for dewatering extends well below the planned subgrade, heave and consequent recompression are decreased by the application of capillary stresses. If groundwater level is restored after construction, the loads remove equals the depth of excavation times total unit weight of the soil. If groundwater pressures are to be permanently relieved, the load removed equals the total weight of soil above the original water table plus the submerged weight of soil below the original water table. Calculate effective stresses as described in Figure 2 (NAVFAC 7.1, MAY 1982, page 7.1 – 207), and consolidation under structural loads as shown in Figure 3 (NAVFAC 7.1, MAY 1982, page 7.1 – 210).

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4.2.4.5 Others Other ground improvement methods which have also been used in the construction of

embankment on soft ground or reclamation works are:-

1. Vacuum Loaded Horizontal Drains 2. Sand Spreading 3. Stone Columns etc.

54

Maritime Unit Pile Foundation Design

CHAPTER 5

PILE FOUNDATION DESIGN 5.0 INTRODUCTION

In view of the many uncertainties inherent in the design of piles, it is difficult to predict with accuracy the behavior of a pile. Even with the use of sophisticated analyses. The actual performance of single piles is best verified by a load test, and foundation performance by building settlement monitoring. In this guideline, reference has been made to published codes, textbooks and other relevant information. The designer is strongly advised to consult the original publications for full details of any particular subject.

Pile design is not complete upon the production of construction drawings. Continual

involvement of the designer is essential in checking the validity of both the geological model and the design assumptions as construction proceeds. As the installation method may significantly affect pile performance, it is most important that experienced and competent specialist contractors are employed and their work adequately supervised by suitable qualified and experienced engineers who should be knowledgeable about the basic of the design.

In common with other types of geotechnical structure, professional judgment and

engineering common sense must be exercised when designing and constructing piles.

It is important that the engineer planning the site investigation and designing the foundations liaises closely with the designer of the superstructure and the project coordinator so that specific requirement and site constraints are fully understood by the project team. 5.1 PILE DESIGN PROCEDURES

Methods based on engineering principles of varying degrees of sophistication are available as a framework for pile design. All design procedures can be broadly divided into four categories: -

1. Empirical ‘rules-of-thumb’ 2. Semi-empirical correlations with in-situ test results

3. Rational methods based on simplified soil mechanics or rock mechanics theories

4. Advanced analytical (or numerical) techniques

55


A judgment has to be made on the choice of an appropriate design method for a given project. In principle, in choosing an appropriate design approach, relevant factors that should be considered include: -

1. The ground conditions

2. Nature of the project

3. Comparable past experience

5.2 SELECTION OF PILE TYPES

One of the most critical steps in analyzing pile foundations is the selection of pile types that are applicable to specific site conditions. To systematically select or eliminate types of piles, the following steps should be considered: -

1. Identify the type of superstructure and loads to be applied to the foundation.

2. Define and summarize subsurface conditions.

3. Subjectively assess the applicability of each type of piles for their capability of

carrying the required loads and estimate the amount of settlement that is likely. Refer to Table 5.1 and 5.2 for pile selection chart and summary of applicable soil conditions for different foundation types. Select and recommend the foundation type that meets structure requirements, is best suited for site subsurface conditions, and is the most economical.

4. Eliminate obviously unsuitable foundation/ piles types and prepare detailed studies

and/ or tentative design for selected pile type: -

a. Determine design criteria and factors to be considered. b. Select pile type, size and length (To comply with design criteria).

c. Check pile capacity (depends on the soil in which it lies, whether it be cohesive

or cohesionless or whether pile sockets in rock).

d. Check deformation/ settlement.

e. Check structural capacity (discount for slenderness and joints)

f. Pile group analysis.

5. Review and check the foundation design requirement, e.g. environmental factors, design loads and allowable settlement.

56


6. Evaluated the anticipated construction conditions and procedures (incorporated local experiences and practice).

5.3 PILE DESIGN CRITERIA

The general pile design criteria and considerations are as follows: - 1. The pile material itself must not be structurally over stressed during handling,

installation and working conditions. This criterion requires compliance with the structural and geotechnical requirements based on code of practice and experiences. Generally, structural requirements for precast concrete piles are given in Appendix A (MS 1314, 1993).

2. There must be an adequate factor of safety (FOS) against failure (see 5.3.1). FOS for

geotechnical capacity should be at least 2 based on lower bound shear strength obtained from adequate site investigation. This criterion is to cater for statistical uncertainty or risk factors.

3. The total and differential settlement under the working load must be within tolerable

limits of the structure. Angular distortion shall not exceed 1:150 for framed R.C structures. This criterion is to ensure the superstructure is not over stressed. Piles settle less than 12 mm at design load are generally satisfactory for R.C framed structures.

4. Control of the installation effects of the structures and its necessary construction

operations to limit noise level and displacement or movement of ground at and under nearby piles, buildings, roads, utilities to tolerable amount both during and after the work shall be specified. This criterion is commonly and conveniently overlooked when detail information is not available.

5. Durability aspects and quality control must comply with BS 8004 and JKR standard

specification for precast concrete piles in building projects (1991). For precast concrete piles, MS 1314 (1993) shall be complied in respect of production quality control and minimum structural requirements.

6. Other important design criteria that should be considered are: -

a. Possible scour and its effect on pile capacity

b. Pile group effect

c. Negative friction of pile in settling ground

57


Table 5.1: Pile Selection Chart

Type of Piles Preformed

Design Consideration

Bak

au P

iles

Tim

ber P

iles

Prec

ast R

.C

Pile

s PS

C P

iles

Spun

Pile

s St

eel H

–

Pile

s St

eel P

ipe

Pile

s

Bor

ed P

iles

Mic

ropi

les

<100 kN / / ? ? ? ? ? Χ ? 100-300 / / / ? ? / / Χ / 300-600 ? / / / / / / / / 600-1100 Χ ? / / / / / / /

1100-2000 Χ ? / / / / / / /

2000-5000 Χ Χ / / / / / / ?

5000-10000 Χ Χ / / / / / / ?

Scal

e of

Loa

d (S

truct

ural

)

Compressive Load per Column

>10000 Χ Χ ? / / / / / ? D ≤ 5m ? ? ? ? ? ? ? ? / 5 – 12m / / / / / / / / / 12 – 24m Χ Χ / / / / / / /

24 – 34m Χ Χ / / / / / / ?

Mainly End – Bearing (D

= Anticipated

Depth of Bearing) 34 –

60m Χ Χ ? ? / ? / ?

Mainly Frictional / / / / / ? / / ?

Bea

ring

Cap

acity

Partly Friction + Partly End Bearing / / / / / / / / ?

Limestone Formation Χ ? ? ? ? / ? ? /

Weathered Rock/ Soft Rock Χ Χ / / / / / / /

Rock (RQD > 70%) Χ Χ ? ? ? / / / /

Geo

tech

nnic

al

Type

of B

earin

g La

yer

Dense/ Very Dense Sand Χ ? / / / / / ? /

58


Soft SPT< 4 / / / / / / / / /

M. Stiff SPT = 4-15

/ / / / / / / / /

V. Stiff Spt = 15-32

? / / / / / / / /

Cohesive Soil

Hard SPT>32 Χ ? / / / / / / /

Loose SPT < 10

/ / / / / / / / /

M.Dense SPT = 10-30

? / / / / / / / /

Dense SPT = 30-50

Χ ? / / / / / / /

Cohesionless Soil

V.Dense SPT > 50

Χ Χ / / / / / / /

S < 100mm Χ ? / / / / / / /

100 – 1000mm Χ Χ ? ? ? / / / /

1000 – 3000mm Χ Χ ? ? ? ? ? ? /

Type

of

Int.

Laye

r (C

ontin

ued)

Soil With Some Boulders/ Cobles (S = Size)

> 3000mm Χ Χ ? ? ? ? ? ? /

Above Pile Cap / / / / / / / / /

Geo

tech

nica

l

Grround Water Below Pile Cap Χ / / / / / / / /

Noise : Vibration : Counter Measures Required

/ / ? ? ? ? ? / / Environment

Prevention of Effects on Adjoining Structures ? ? ? ? ? ? ? ? /

Unit Cost RM/ Ton/ Ft 0.5-2.5 0.3 – 2.0 0.8-3.5 0.4-2.0

0.4-2.0

Note: - / Indicates that pile type is suitable Χ Indicates that the pile is not suitable

? Indicates that the use of the pile type is doubtful unless additional measures taken

59


Table 5.2: Preliminary Foundation Type Selection

Foundation Type Use Applicable Soil Conditions

Spread Footing • Individual columns, walls, bridge piers

• Any conditions where bearing capacity is adequate for applied load.

• May use on single stratum; firm layer over soft layer or soft layer over firm layer.

• Check immediate, differential, and consolidation settlements.

Mat Foundation • Same as spread and

wall footings. • Very heavy column

loads. • Usually reduces

differential settlements and total settlements.

• Generally soil bearing value is less than for spread footings; over one-half area of building covered by individual footings.

• Check settlements.

Friction Piles • In groups to carry heavy column, wall loads.

• Required pile cap.

• Low strength surface and near surface soils.

• Soils of high bearing capacity 18-45m below ground surface, but by disturbing load along pile shaft solid strength is adequate.

• Corrosive soils may require use of timber or concrete pile material.

End Bearing Piles • In groups (at least

2) to carry heavy column, wall loads.

• Require pile cap.


• End of pile located on soils 7.5-30m below ground surface.

Drilled Shaft (End Bearing)

• Larger column loads than for piles but eliminates pile cap by using caissons as column extension.


• End of shaft located on soils 7.5-30m below ground surface.

Sheet pile • Temporary retaining structures for excavations, alloy waterfront structures, cofferdams.

• Any soils • Waterfront structures may require

special or corrosion protection. • Cofferdams require control of fill

material.

60


5.3.1 Recommended Factors of Safety

The following considerations should be taken into account in the selection of the

appropriate factors of safety: -

1. There should be an adequate safety factor against failure of structural members in accordance with appropriate structural codes.

2. There must be an adequate global safety factor on ultimate bearing capacity of the

ground. Terzaghi and Peck (1967) proposed the minimum acceptable factor of safety to be between 2 and 3 for compression loading. The factor of safety should be selected with regard to importance of structure, consequence of failure, the nature and variability of the ground, reliability of the calculation method and design parameters, extend of previous experience and number of load tests on preliminary piles. The factors as summarized in Table 5.3 for piles in soils should be applied to the sum of the shaft and base resistance.

3. The assessment of working load should additionally be checked for minimum

‘mobilization’ factors fs and fb on the skin friction and base resistance respectively as given in Table 5.4.

4. Settlement considerations particularly for sensitive structures, may govern the

allowable loads on piles and the global safety factor and/ or ‘mobilization’ factors may need to be higher than those given in (2) & (3) above.

5. Where significant cyclic, vibratory or impact loads are envisaged or the properties of

the ground are expected to deteriorate significantly with time, the minimum global factor of safety to be adopted may need to be higher than those in (2), (3) and (4) above.

The minimum factor of safety recommended for pile design is intended to be used in

conjunction with best estimates of resistance.

61


Table 5.3: Minimum Global Factors of Safety for Piles in Soil

Minimum Global Factor of Safety against Shear Failure of the Ground Method of Determining Pile Capacity Compression Tension Lateral

Theoretical or semi-empirical method not verified by load tests on preliminary piles 3.0 3.5 3.0

Theoretical or semi-empirical method verified by a sufficient number of load tests on preliminary piles 2.0 2.5 2.0

Notes: 1. Table based on American Society of Civil Engineers (1993) 2. Assessment of the number of preliminary piles to be load tested is discussed in other

section. 3. Factor of safety against overstressing of pile materials should be in accordance with

relevant structural design codes. Alternatively, prescribed allowable structural stresses may be adopted as appropriate.

4. In most instances, working load will be governed by consideration of limiting pile movement, and higher factors of safety (or ‘serviceability’ factors) may be required.

Table 5.4: Minimum Mobilization Factors for Skin Friction and Base Resistance

Material Mobilization Factor for Skin Friction, fs

Mobilization Factor for Base Resistance, fb

Granular Soils 1.5 3-5 Clays 1.2 3-5

Notes: 1. Mobilization factor for base resistance depends very much on construction.

Recommended minimum factors assume good workmanship without presence of debris, etc. giving rise to a ‘soft’ toe and are based on available local instrumented load tests on friction piles in granitic saprolites. Mobilization factors for base resistance also depend on the ratio of skin friction to base resistance. The higher the ratio, the lower is the mobilization factor.

2. Noting that the movement required mobilizing the ultimate base resistance are about 2% to 5% of the pile diameter for driven piles, and about 10% to 20% of the pile diameter for bored piles, lower mobilization factor may be used for driven piles.

3. In stiff clays, it is common to limit the peak average skin friction to 100 kPa and the mobilized base pressure at working load to a nominal value of 550 to 600 kPa for settlement considerations, unless higher values can be justified by load tests.

4. Where designer judges that significant mobilization of base resistance cannot be relied on at working load due to possible effects of construction, a design approach which is sometimes advocated (e.g. Toh et al, 1989; Broms & Chang, 1990) is to ignore the base resistance altogether in determining the design working load with a suitable mobilization factor on skin friction alone (e.g. 1.5). Base resistance is treated as an added safety margin against ultimate failure and considered in checking for the factor of safety against ultimate failure.

5. Lower mobilization factor for base resistance may be adopted for end-bearing piles provided it can be justified by settlement analyses that the design limiting settlement can be satisfied.

62


5.4 ESTIMATION of PILE CAPACITY Qu G.L

Qu = Qs + Qp Qu = ∫ f p d h + q Ap Qu = fa As + q Ap D

f Qu = Ultimate Pile Capacity As = Shaft Area fa = Average Shaft Friction Ap = Cross-Sectional Area of Pile Tip

f = Unit Shaft Friction; May Vary With Depth h q

p = Pile Circumference or Perimeter q = Unit End Bearing

5.4.1 Use of Soil Mechanics Principles

1. Cohesionless/ Granular Soils

a. Bored Piles

i. Ultimate End Bearing Stress

qb = Nq. σv’ Where; σv’ = Vertical Effective Stress Nq = Bearing Capacity Coef (Fig. 5.1)

63


ii. Ultimate Shaft Friction

τs = c’ + Ks. σv’.tan δs τs = β.σv’ (when c’ is assume to be zero) Where;

Ks = Coeff. of horizontal pressure which

depends on the relative density and state of the soil, method of pile installation, and material, length and shape of the pile (Table 5.6)

σv’ = Mean vertical effective stress δs = Angle of friction along pile/ soil interface

(Table 5.7) β = Shaft friction coefficient (Table 5.8)

It must be noted that in relating τs to σv’ with the use of the β factor, it is assumed that there is no cohesion component (c’).

b. Driven Piles

• The concepts presented for the calculation of end bearing capacity

and skin friction for bored piles in granular soils also apply to driven piles in granular soils.

• The main difference lies in the choice of design parameters, which should reflect the pile-soil system involving effects of densification and increase in horizontal stresses in the ground due to pile driving.

• The calculated ultimate base stress should be limited to 15 MPa (Tomlinson, 1994). Higher values can be used if supported by pile load tests.

2. Cohesive Soils

a. Bored Piles

i. Ultimate End Bearing Stress

qb = Nc.Cu

Where;

Cu = Undrained Shear Strength, determined from Unconsolidated Undrained Triaxial Compression Tests.

Nc = Bearing Capacity Coefficient, it is generally be taken as 9 when the location

64


of the pile base below the ground surface exceeds four times the pile diameter. For shallower piles, the Nc factor may be determined following Skempton (1951).

The base resistance is fully mobilized only until the pile settlement amounts to 10 to 20 percent of the base diameter (Whitaker and Cooke, 1966).

ii. Ultimate Skin Friction

τs = α.Cu

Where;

α = Adhesion Factor, Whitaker and Cooke (1966) reported that α value lies in the range of 0.3 to 0.6, while Tomlinson (1994) and Reese & O’ Neill (1988) reported α values in the range of 0.4 to 0.9.

Burland & Twine (1989) suggested that the value of skin

friction for piles in over-consolidated / stiff clays be estimated from the following expression: -

τs = Ks.σv’.tan ∅r’ Where; Ks can be assumed to be Ko and

∅r’ = Angle of friction which are at or close to the residual angle of shearing resistance.

Both the undrained and effective stress methods can generally be used for the design of piles in clays. The use of undrained method relies on an adequate local database of test results. In the case where piles are subject to significant variations in stress levels after installation (e.g. excavation, rise in groundwater table), the use of the effective stress method is recommended, taking due account of the effects on the Ks values due to the stress changes.

b. Driven Piles

• The design of Driven Piles in cohesive soils can be done using a

design curve shown in Figure 5.2 by Nowacki et al (1992).

65


• The Design should be checked by using equation outlined in the calculation of end bearing capacity and skin friction for bored piles.

5.4.2 Correlation With Standard Penetration Test (SPT)

It is a semi-empirical correlation developed relating both skin friction and end bearing capacity of piles founded in granular soils to N values. The N values generally refer to uncorrected values before pile installation.

1. End Bearing

qb = 4N – in sand

qb = 2.5N – in silt

qb = 1N or 9.Cu – in clay

2. Skin Friction

τs = 0.02 N, for driven piles in sand τs = 0.017 N, for driven piles in silt τs = 0.006 N, for bored piles in sand τs = 0.01 N, for H – Piles Where; N = SPT in the vicinity of pile tip

Ñ = Average SPT along pile shaft

5.5 NEGETIVE SKIN FRICTION

Negative Skin Friction occurs on the part of the shaft along which the downward

movement of the surrounding soils exceeds the settlement of the pile. The magnitudes of Negative Skin Friction that can be transferred to a pile depend on (Bjerrum, 1973): -

1. Pile material 2. Method of pile construction

66


3. Nature of soil

4. Amount and rate of relative movement between the soil and the pile.

In determining the amount of Negative Skin Friction, it would be necessary to estimate the position of the neutral point, i.e. the level where the settlement of the pile equals the settlement of the surrounding ground. For end-bearing piles, the neutral point will be located close to the base of the compressible stratum.

5.5.1 Calculation of Negative Skin Friction

Various methods of calculating the negative skin friction. However, only the effective stress or β method will be outlined in these guidelines. Using the effective stress approach, the ultimate negative skin friction can be estimated as follows: -

fn = β.σv’ Where; fn = Ultimate Negative Skin Friction σv’ = Effective Vertical Stress β = Empirical factor obtained from full-scale load test or based on the following

table for preliminary design purposes.

Table 5.5: Empirical factor

Soil Type β (After Garlarger et al, 1973) Clay 0.20 – 0.25 Silt 0.25 – 0.35

Sand 0.35 – 0.50

The neutral point may be taken to be at the pile base for an end – bearing pile that has

been installed through a thick layer of soft clay down to rock or to a stratum with high bearing capacity. For a pile whose tip could settle when loaded, the ratio of the depth of the neutral point to the length of the pile in compressible strata may be roughly approximated as 0.75 (NAVFAC, 1982). However, the reduction in negative skin friction is normally not very significant and may be conservatively ignored.

The way safety factors are incorporated in the design of piles subjected to negative skin friction requires careful consideration. In the case of a pile embedded in a compressible material, the problem of negative skin friction may be regarded as a settlement problem and the overall factor of safety against ultimate failure remains unchanged (Fellenius, 1989). However, in the case of a pile founded on rock, it becomes a bearing or structural capacity problem (Canadian Geotechnical Society, 1992).

67


If the pile settlement under working load is small, e.g. short large-diameter piles end-bearing on rock, there may not be significant relief of negative skin friction due to pile settlement and the following method suggested by NAVFAC (1982) should be used: -

Qall = (Qult/ Fs) - Pu

Where; Qall = The allowable pile load Qult = The ultimate resistance below the neutral point Fs = Global factor of safety Pu = Ultimate negative skin friction

It should be noted that negative skin friction can have the dual effect of inducing

downdrag and reducing the available capacity as a result of reduction in overburden pressure.

5.6 SETTLEMENT OF PILES and PILE GROUPS There exist many procedures for estimating pile foundation settlements, ranging from relatively simple hand calculation methods to sophisticated nonlinear finite element analyses, and it seems appropriate to review and assess some of these methods. The procedures outlined below enable a rough estimate to be made of the settlement of a group of piles or of an individual pile within a group. The interaction between piles and the surrounding soil is complex and not properly understood: consequently, values obtained by the simple hand calculation methods given below should not be relied on to give accurate values.

68


Figure 5.1: Variation of Failure Modes and Factor Nq

69


Table 5.6: Typical Values of Angle of Friction at Pile/ Soil Interface in Granular Soils

Pile/ Soil Interface Condition δs/φ’ Steel/ sand Cast-in-place concrete/ sand Precast concrete/ sand

0.5 to 0.9 1.0

0.8 to 1.0

Legend: φ’ = Angle of shearing resistance δs = Angle of friction at pile/ soil interface Notes: (1) Table based on Kulhawy (1984) (2) Where steel is considered rough (corrugated), δs/φ’ ratio will be near upper end of the

above range.

Table 5.7: Typical Values of Coefficient of Horizontal Pressure on Pile under Compression

Pile Type Ks/ Ko

Large-displacement piles Small-displacement piles3 Replacement piles

1 to 2 0.75 to 1.25 0.7 to 1.0

Legend: Ko = Coefficient of earth pressure at rest Ks = Coefficient of horizontal pressure on pile Notes: (1) Table based on Kulhawy (1984) (2) In granular soils, Ko may generally be taken as (1-sinφ’) where φ’ is the angle of

shearing resistance unless they have been over-consolidated or preloaded. (3) In clays, Ko will be related to the overcosolidation ratio, OCR (Meyerhof, 1988).

Table 5.8: Typical Values of Skin Friction Coefficient in Sand

Type of Piles Type of Soils Shaft Friction Coefficient, βDriven Piles Loose sand 0.4 to 1.0 Driven Piles Dense Sand 1.0 to 2.0 Bored Piles Loose sand 0.15 to 0.3 Bored Piles Dense sand 0.25 to 0.6

Notes: (1) Table based on Davies & Chan (1981)

70


5.6.1 Settlement of an Individual Pile in Clay The settlement of a pile in a layer of finite thickness, underlain by an incompressible material, can be obtained from the expression:-

ρ = Q . Ip L. Es

Where;

Q is the load on the pile L is the pile length Es is Young’s modulus for the soil: effectively for long term settlement, Es = (1 + ν)(1 - 2ν) Mv (1 - ν)

Where Mv is the average value for the layer and ν is Poisson’s ratio which can be taken as 0.4 for over consolidated clays and firm or stiff normally consolidated clays, and as 0.2 for soft to firm normally consolidated clays. Ip is an influence factor, obtained from Figure 5.2 or 5.3.

Care must be taken that consistent units are used throughout.

Figure 5.2: Values of influence factor Ip for a pile in a compressible stratum of finite depth; Poisson’s ratio = 0.20

71


Figure 5.3: Values of influence factor Ip for a pile in a compressible stratum of finite depth;

Poisson’s ratio = 0.40

5.6.2 Settlement of Piles Within a Group In Clay The settlement ρi of pile i within a group can be estimated from the expression:-

k

ρi = ρl (Qi + Σ Qj. αij) j=l

j≠i

Where;

ρl is the settlement of pile I under unit load Qi is the load on pile I

Qj is the load on pile j, where j becomes each of the other piles in the group, in turn αij is the interaction factor between piles I and j. The value of α depends on the pile spacing and is obtained from Figure 5.4.

72


Figure 5.4: Values of interaction factor α for piles in a compressible stratum of finite depth;

Poisson’s ratio = 0.50

Although the graph is drawn for ν = 0.5, the value of ν is not critical and the graph can be used with sufficient accuracy for alls values of ν. For a pile within a group, it will usually be found that the settlement of the pile due to the influence of surrounding piles far exceeds the settlement due to the load on the pile itself. Thus, although the settlement of a single pile in a load test may seem to be very small, the settlement of a completed structure supported on a group of similar piles may be quite large. The process of summing the interactions of every pile with every other pile in a large group can be tedious and time consuming. However, it will usually be found that most piles in the group are so far away that their influence can be ignored, or perhaps a simple allowance can be made for the total effect of all piles beyond a certain distance. Where piles are not all the same length the effect on the H/L ratio is usually small, so the method can still be used. Where piles have different diameters or widths, the S/B ratio of pile j should be used to obtain the value of αij. 5.6.3 Settlement of An Individual Pile In Sand or Gravel The settlement of a pile driven into dense granular soil is usually very small and, since settlement in granular soils is rapid, there is usually no problem. With bored piles or piles driven into loose granular soil, settlement may be appreciable but there is no accepted method of predicting settlements with any degree of accuracy. As a very rough approximation, the

73


vertical displacement of the pile can be estimated by approximating it to a point load at the pile base. However, the only reliable method of obtaining the deflection of a pile in a granular soil is to carry out a pile test. 5.6.4 Settlement of A Pile Group In Sand or Gravel A rough guide to the settlement of a pile group in granular soil, related to the settlement of a single pile, can be obtained from information given by Skempton, Yassin and Gibson, shown in Figure 5.5, where :

α = _ (Settlement of Pile Group) _ (Settlement of single pile under same working load)

Figure 5.5: Ratio of Settlement of a Pile Group to Settlement of a

Single Pile.

74


5.6.5 A Simple Method of Estimating The Settlement of A Pile Group

The average settlement of a pile group can be estimated by treating the group as an equivalent foundation with a plan area equal to the area of group.

For predominantly end – bearing piles (in sands), the foundation is assumed to be at

the base of the piles. For friction piles (in clays), it it assumed to be two thirds of the way down the embedded length or, if there is an overlying granular or soft clay layer, two thirds of the way down the length embedded in the clay bearing stratum. 5.7 STRUCTURAL CAPACITY of PILES

1. Structural capacity of R.C. piles Qa = 0.25.fcu.Ac kN Where; fcu = Specified cube strength at 28 days Ac = Gross cross sectional area of the pile

2. Structural capacity of steel piles

Qa = 0.3.fy.As kN – For driven piles

Qa = 0.5.fy.As kN – For jacked-in piles

Where;

fy = Yeild strength of the steel

As = Cross sectional area of the pile

3. Structural capacity of timber piles

Recommended by pile manufacturers, normally about 100 kN – 120 kN for 125mm x 125mm and 150 kN – 180 kN for 150mm x 150mm timber piles.

75

Maritime Unit Geotechnical Design Checklist

GEOTECHNICAL DESIGN

CHECKLIST

Maritime Unit Geotechnical Design Checklist-Appendix A

No. KeluaranAmenmend No

JKR MALAYSIA DatePage

Checklist : Yes No N/A1.0 Site Investigation 1.1 SI Proposal 1.1.1 Satisfaction of SI Methods and Locations 1.1.2 SI Drawings 1.1.3 Estimated Cost (BQ) 1.1.4 Specification 1.1.5 SI Works Programme

1.2 SI Report 1.2.1 Authentication of The Factual Report by SI Consultant/ Contractors 1.2.2 Project Brief 1.2.3 Method Statement of SI 1.2.4 Field Investigation Result 1.2.5 Laboratory Test Result 1.2.6 Summary of Laboratory Test Result. 1.2.7 Photograph of SI Works

2.0 Geotechnical Interpretation and Design 2.1 Geotechnical Interpretation and Design Report 2.1.1 Geotechnical Evaluations 2.1.1.1 Define Subsoil Profile 2.1.1.2 Interpretation of Lab and In-Situ Test Results 2.1.1.3 Description of Soil Properties 2.1.1.4 Selection of Geotechnical Parameters 2.1.1.5 Conclusion

2.1.2 Geotechnical Design/ Analyses (Refer Appendix B,C,D and E) 2.1.2.1 Stability Analysis 2.1.2.2 Settlement Analysis 2.1.2.3 Ground Treatment 2.1.2.4 Foundation

2.2 Construction Drawings 2.2.1 Descripencies of Construction Drawings and Design 2.2.1.1 Specification 2.2.1.2 Detailings 2.2.2 Authentication of The Drawings Professional Engineers

Designer.

Name/ Chop/ Date

Checker.

Name/ Chop/ Date

Remarks by JKR

Unit maritim, Cawangan Pangkalan Udara dan Maritim, Tingkat 5, Blok B,

Kompleks Kerjaraya Malaysia, Jalan Sultan Salehuddin, 50582 Kuala Lumpur.

Document Ref. No


Item

Project : Designer :Date :Checker :Date :

Geotechnical Design Works Were Carried Out in accordance with the specification and other code specified and good engineering practiceWorks need to be review. Re-submission not requiredWorks need to be review. Re-submission required

The proposed method/ system is conceptually appropriate of their respective functions. In the opinion of the checker, the designer has provided a reasonable design with the available data.

PROPERTY OF JKR MALAYSIA 76

Maritime Unit Geotechnical Design Checklist-Appendix B



Checklist : Yes No N/A1.0 Configuration of Embankment 1.1 Gradient of The Side Slope 1.2 Width of The Embankment 1.3 Height of The Embankment 1.4 Slope Stabilization (if any) 1.5 Slope Protection (if any)

2.0 Soil Parameters 2.1 Accuracy of Soil Parameters Used 2.2 Consideration of Ground Water Table

3.0 Methods of Analysis 3.1 Applicability of Calculation/ Analysis Methods Used 3.2 Satisfaction of FOS Obtained

Designer.

Name/ Chop/ Date

Checker.

Name/ Chop/ Date

Geotechnical Design Works Were Carried Out in accordance with the specification and other code specified and good engineering practiceIndicated works need to be review. Re-submission not requiredIndicated works need to be review. Re-submission required



Remarks by JKR

UNIT MARITIM, CAWANGAN PANGKALAN UDARA DAN MARITIM, TINGKAT 5,

BLOK B, KOMPLEKS KERJARAYA MALAYSIA, JALAN SULTAN SALEHUDDIN,

50582 KUALA LUMPUR.

Document Ref. No

Stability Analysis Checklist

Item


Maritime Unit Geotechnical Design Checklist-Appendix C



Checklist : Yes No N/A1.0 Configuration of Embankment 1.1 Gradient of The Side Slope 1.2 Width of The Embankment 1.3 Height of The Embankment 1.4 Surcharge (if any) 1.5 Ground Improvement methods (if any) 1.5.1 Applicability of Ground Improve- ment Design

2.0 Soil Parameters 2.1 Accuracy of Soil Parameters Used 2.2 Consideration of Ground Water Table

3.0 Methods of Analysis 3.1 Applicability of Calculation/ Analysis methods Used 3.2 Acceptability of Total Settlement Rate i. Total Settlement =________ mm ii. 90% Concolidation :- a. Without Ground Improvement = _______months b. With Ground Improvement = _______months

Designer.

Name/ Chop/ Date

Checker.

Name/ Chop/ Date




Remarks by JKR



50582 KUALA LUMPUR.

Document Ref. No

Settlement Analysis Checklist

Item


Maritime Unit Geotechnical Design Checklist-Appendix D



Checklist : Yes No N/A1.0 Cause of The Treatment 1.1 Stability 1.2 Settlement

2.0 Type of Ground Treatment 2.1 Surcharge Without Vertical Drain 2.2 Surcharge With Vertical Drain 2.3 Sand/ Laterite Replacement 2.3.1 Partial Replacement 2.3.2 Total Replacement 2.4 Pile Embankment 2.4.1 Floating Piles 2.4.2 End Bearing Piles 2.5 Jet Grouting 2.6 Sand Compaction Piles 2.7 Lime or Cement Columns 2.8 Stone Columns 2.9 Soil/ Slope Reinforcement by Geotextile 2.10 Dinamic Compaction 2.11 Electro - Osmosis 2.12 Others

3.0 Applicability of The Methods 3.1 Constructionability 3.2 Functionality 3.3 Cost Effectiveness 3.4 Technical Soundness 3.5 Time Schedule 3.6 Environmental Friendly

4.0 Ground Treatment Design 4.1 Satisfaction of Ground Treatment Design.(if any)

Designer.

Name/ Chop/ Date

Checker.

Name/ Chop/ Date




Remarks by JKR



50582 KUALA LUMPUR.

Document Ref. No

Ground Treatment Design Checklist

Item


Maritime Unit Geotechnical Design Checklist-Appendix E



Checklist : Yes No N/A1.0 Type of Foundation 1.1 Shallow Foundation 1.2 Deep Foundation (pile)

2.0 Type of Pile Foundation 2.1 Bakau Piles 2.2 Treated Timber Piles 2.3 Precast R.C. Piles 2.4 Prestressed Concrete Piles 2.5 Bored Piles 2.6 Steel Piles 2.7 Micropiles 2.8 Others

3.0 Applicability of The Foundation 3.1 Constructionability 3.2 Functionality 3.3 Cost Effectiveness 3.4 Technical Soundness 3.5 Time Schedule 3.6 Environmental Friendly

4.0 Pile Foundation Design 3.1 Determination of Design Criteria and Factors To Be Considered 3.2 Compliances With Design Criteria of Pile Type, Size and Length 3.3 Evaluation of Geotechnical Pile Capacity 3.3.1 Accuracy of Soil Parameters Used 3.3.2 Consideration of Ground Water Table 3.4 Evaluation of Deformation/ Settlement 3.5 Evaluation of Structural Pile Capacity 3.6 Pile Group Analysis (if any)

Designer.

Name/ Chop/ Date

Checker.

Name/ Chop/ Date




Remarks by JKR



50582 KUALA LUMPUR.

Document Ref. No

Foundation Design Checklist

Item


Maritime Unit Geotechnical Design Guidelines - Appendix 1a

FLOW CHART FOR GEOTECHNICAL DESIGN WORKS

81

Maritime Unit Geotechnical Design Guidelines - Appendix 1b

FLOW CHART FOR SITE INVESTIGATION WORKS

82

Maritime Unit Geotechnical Design Guidelines - Appendix 1c

FLOW CHART FOR STABILITY ANALYSIS

83

Maritime Unit Geotechnical Design Guidelines - Appendix 1d

FLOW CHART FOR SETTLEMENT ANALYSIS

84

geotechnical design guidelines -...

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