introduction to road soil characterization - u of s ... course notes-march 17-19 201… ·...

1

Introduction to Road Soil CharacterizationCharacterization

By:Dr. Curtis F. Berthelot P.Eng.

Department of Civil and Geological EngineeringC t f E ll f T t ti d I f t tCentre of Excellence for Transportation and Infrastructure

Road Soil Introduction

Roads are constructed of layered heterogeneous multiphase geo-materials that exhibit internal friction,

h i dil i d i l l i b h icohesion, dilation, and viscoelastoplastic behavior under load.

Behavior is often influenced by confinement because the material is non-linear stress dependent.

Several methods have evolved to quantify performance-related properties or road soils.

Road Soil Characterization2

2

Granular Pavement Structure

Asphalt wearing coarse

S bbGranular Base

Subgrade: in-situ material used to construct grade. Subbase: select material (usually low quality granular)

that is borrowed from a pit and placed over the b d

Subgrade

Subbase


subgrade. Base: high quality granular layer placed directly under

asphalt concrete. Wearing coarse : asphaltic or hydraulic bound

aggregate

PCC Cross Section

Granular Base

Portland Cement Concrete

Subgrade

Granular Base

Subgrade: in-situ material used to construct grade.

Subbase: none.

Base: high quality coarse crush with high air voids for


g q y gdrainage.

Wearing coarse : Portland Cement Concrete

3

Permanent Deformation HMAC Materials

Pouching

Asphalt Concrete Pavement Failures and Distresses

5

Permanent Deformation Substructure


6

4

Fatigue Cracking


7

Fatigue Cracking and Substructure Rutting


8

5

Frost Action


9

Frost Action


10

6

Soil Definition

Soil: • All earthen materials including:• Organics• Sands• Clays• Gravels• Silts


Soil Definition

Definition of Soil and Soil Components:

• Soil is a layer of disintegrated rock material lying on the surface of the earth

Two broad groups of soils:

• Residual Soils

• Soils developed in place from the rock or parent soil

• Transported Soils


• Transported Soils

• Residual soils eroded and redeposited by wind, ice or water

7

Road Soil Characterization

Physical properties:

• Grain size analysis (AASHTO T27, ASTM C136)

• Sand equivalent (AASHTO T176)

• Classification (ASTM D3282):

• Unified Soil Classification System

• AASHTO



Phenomenological properties:

• Atterberg limits and plasticity index (ASTM D4318, AASHTO T89 , AASHTO T90)

• Proctor water-density (AASHTO T99, ASTM D 698)

• California bearing ratio (AASHTO T193, ASTM D1883)

• Hveem Resistance


8

Soil Volumetrics

Soil mass is comprised of:• Soil• Air• Water• Soil-water interface• Water-air interface


Soil Volumetrics

AirW Ai I f

Soil Solids

Water

Water-Air Interface

Soil-Water InterfaceVT

VW WW

VS WS

VV

WT


Soil SolidsS WS

9

Grain Size Analysis

Aggregate gradation is the distribution of particle sizes.

AASHTO T27, ASTM C136.

Size of soil particles has an effect on the engineering behavior of soil.

Affects strength through inter-particle interlock.

Affects mixing: more fines = more surface area to coat.

Well-graded soils compact to higher density increasing tr n th


strength.

Grain Size Analysis

Well GradedUniformly Graded


10

Mechanical Sieve:

• Used to determine particle size distribution of

Grain Size Analysis

aggregates larger than 0.075mm

• Weighed sample of aggregate passed through series of different sized screens

• Results are used to classify soils

May have wet sieve performed first to accurately quantify fines in the material.


quantify fines in the material.

Aggregate Particle Size/Gradation


Individual Sieve Stack in Mechanical Shaker

11

Wet Sieve Analysis


Wet Sieve Analysis


12

Aggregate Particle Size/Gradation

Mineral Filler: aggregate with at least 70% passing the 75m (No. 200) sieve.

Fine Aggregate: aggregate passing 4.75mm (No. 4); or 2.36mm (No. 8); or 2.00mm (No. 10) sieve.

Coarse Aggregate: aggregate retained on 4.75mm (No. 4); or 2.36mm (No. 8); or 2.00mm (No. 10) sieve.

Nominal Maximum Size: smallest sieve size through which 90% passes.


Maximum Size: smallest sieve size through which 100% passes.

Grain Size Analysis

80

100

Th

an

0

20

40

60

0.001 0.010 0.100 1.000 10.000

Per

cen

t F

iner

T


0.001 0.010 0.100 1.000 10.000

Grain Size (mm)Clay Subgrade (Hydrometer Sieve) Clay Subgrade (Mechanical Sieve)Clay Till Subgrade (Hydrometer Sieve) Clay Till Subgrade (Mechanical Sieve)Subbase (Mechanical Sieve) Granular Base (Mechanical Sieve)

13

Hydrometer Sieve:

• Fine particles smaller than 0.075 mm are further

Grain Size Analysis

graded by a hydrometer analysis

• Mix fines with water/flocculants and measure density of water as the particles settle

• Large particles settle faster than fine particles

• Settlement changes density of water


Hydrometer Grain Size Analysis

Silty-Sand Clay-Till


14

Grain Size Analysis

COS Subbase Aggregate

100

0

20

40

60

80

Per

cen

t F

iner

Th

an


0

0.010 0.100 1.000 10.000

Grain Size (mm)

Gradation Boundaries Mean

Grain Size Analysis

COS Base Aggregate

100

0

20

40

60

80

Per

cen

t F

iner

Th

an

28

0.010 0.100 1.000 10.000

Grain Size (mm)



15

Grain Size Analysis

SDHT Granular Base Type 33

100

0

20

40

60

80

100

Per

cent

Fin

er T

han


0

0.010 0.100 1.000 10.000

Grain Size (mm)


COS Subbase & Base Mean Crossplot

90

100

Grain Size Analysis

20

30

40

50

60

70

80

Per

cen

t F

iner

Th

an

30

0

10

Sieve Size0.45

(mm)

Subbase Base

0.0710.16

0.40 0.90 2.0 5.0 18.012.59.0 16.0 25.0


16

Atterberg Limits

Introduction

• Water significantly affects behavior of fine grained soils

• Different fine grained soils behave differently

• How can different fine grained soils be categorized?


Atterberg Limits

Define water contents at which fine grained soils behavior changes (states of consistency)• U Li it• Upper Limit• Liquid Limit: water content where clay begins to act

like a liquid• Sticky Limit• Cohesion Limit• Plastic Limit: water content where clay begins to

exhibit plasticity


exhibit plasticity• Shrinkage Limit• Plastic Index: LL-PL

17

Atterberg Limits

LiquidState

Free Flow Limit

Liquid Limit

Plastic Limit

Shrinkage Limit

SemisolidState

PlasticState

State

Liquid Limit minusplastic limit equals

plasticity index; equalsrange in moisture

content through whichsoil is plastic


Shrinkage Limit

Dry Limit

SolidState

Atterberg Limits

Plastic Limit Test:

• Sieve soil through #40 (0.425 mm) sieve

• Add enough moisture to be able to knead the material

• Roll soil into 3mm thread

• Plastic limit defined as the point when soil crumbles at 3mm diameter


18

Atterberg Limits


Atterberg Limits


19

Atterberg Limits

Liquid Limit Test:

• Mix fine grained soils with enough water to get soil to consistency of peanut butter

• Spread 1 cm layer into bowl on liquid limit apparatus

• Cut groove into soil

• Drop bowl 1 cm until groove closes 13mm (1/2”)


Atterberg Limits


20

Atterberg Limits


Atterberg Limits


21

Soil Classification

Most common methods:

• USCS: Unified Soil Classification SystemUSCS: Unified Soil Classification System.

• AASHTO: American Association of State Highway and Transportation Officials.


Four main groups of soils:

1 Coarse-grained

USCS Soil Classification

1. Coarse-grained

2. Fine-grained

3. Organic soils

4. Peat

Used by Saskatchewan Highways

Originally developed for airfield construction


g y p

22


Letter system for soil classification:

• G – Gravel

• S – Sand

• M – Silt

• C – Clay

• W – Well Graded

• P – poorly graded

• U – uniformly graded

• L – low liquid limit

• I – intermediate liquid limit

• H – high liquid limit


• V – very high liquid limit

USCS Soil Classification ASTM D 2487

Group symbol Group name

GW well graded gravel, fine to coarse gravel

GP poorly graded gravel

GM silty gravel

GC clayey gravel

SW well graded sand, fine to coarse sand

SP poorly-graded sand

SM silty sand

SC clayey sand

ML silt

CL clay

44

CL clay

OL organic silt, organic clay

MH silt of high plasticity, elastic silt

CH clay of high plasticity, fat clay

OH organic clay, organic silt

Pt peat


23

USCS Soil Classification ASTM D 2487

Major divisionsGroup symbol

Group name

gravel> 50% of coarse

clean gravelGW

well graded gravel, fine to coarse gravel

GP l d d l

Coarse grained soilsmore than 50% retained

on No.200 (0.075 mm) sieve

fraction retained on No.4 (4.75 mm)

sieve

GP poorly graded gravel

gravel with >12% fines

GM silty gravel

GC clayey gravel

sand≥ 50% of coarse fraction passes No.4 (4.75 mm)

sieve

clean sandSW

well graded sand, fine to coarse sand

SP poorly-graded sand

sand with >12% fines

SM silty sand

SC clayey sand

il d l inorganicML silt

45

Fine grained soilsmore than 50% passes

No.200 (0.075 mm) sieve

silt and clayliquid limit < 50

inorganicCL clay

organic OL organic silt, organic clay

silt and clayliquid limit ≥ 50

inorganicMH silt of high plasticity, elastic silt

CH clay of high plasticity, fat clay

organic OH organic clay, organic silt

Highly organic soils Pt peat



50

60

CV

10

20

30

40

Pla

stic

ity

Ind

ex

CI

CH

CL


0

0 10 20 30 40 50 60 70 80 90 100

Liquid Limit (%)

MLCL-ML

24

AASHTO Soil Classification

Developed for “farm to market” road construction.

Based on observed performance of different soils under hi h ( i ibili )highway pavements (moisture susceptibility).

Seven main groups of soils, A-1 to A-7.

Grouped by gradation, liquid limit, and plasticity index.

One of first soils classification schemes related to road performance.

• Correlate subgrade soil type and observed road


Correlate subgrade soil type and observed road performance.


Modified by Highway Research Board and later AASHTO into the present AASHTO Group Index (GI) soil l ifi ti tclassification system.

Categorizes soils into 8 classes based on grain size distribution:

• A-1 to A-3 (well-graded to poor-graded granular soils)

• A-4 to A-7 (fine-grained soils)

Extension of AASHTO soil classification scheme which


further classifies road soils based on correlations of physical soil properties and Atterberg limits to observed road performance.

25


A-1 to A-3: Excellent to good material for subgrade:

• A-1: most stability, less than 50% passing No. 40 sieve, less than 25% passing No. 200 sieve

• A-2: less than 35% passing No. 200 sieve

• A-3: fine sand

A-4 to A-7: Fair to poor material for subgrade materials:

• More than 36% passing No. 200 sieve

S t d b li id li it d l ti it i d


• Separated by liquid limit and plasticity index


Group Index (GI):

• Used to further evaluate soils within a group

• Based on service performance of soils

• Range from 0 to 20• GI = (Fines-35)[0.2+0.005(LL-40)]+0.01(Fines-15) (PI-10)

• Fines = % passing 0.075mm sieve

• LL = Liquid limit

• PI = Plasticity Index


• PI = Plasticity Index

26

AASHTO Road Soil Classification AASHTO M-145 and ASTM D 3282

Usual types of significant constituent materials

Group ClassificationGeneral rating as a

subgradeGeneral Classification

silty or clayey gravel and sandA-2

fine sandA-3

stone fragments, gravel and sand

A-1

excellent to goodGranular Materials (35% or

less passing 0.075 mm)

constituent materialssubgrade

51

clayey soilsA-7

A-5silty soils

A-4

fair to poorSilt-Clay Materials (>35%

passing 0.075 mm)


AASHTO Road Soil Classification AASHTO M-145 and ASTM D 3282

A-7-5 A-7-

A-7

A-6A-5A-4

A-2

A-3

A-1

Group Classification

Silt-Clay Materials (>35% passing 0.075 mm)

Granular Materials (35% or less passing 0.075 mm)

General Classification

41 min40

max41

min40

max41

min40

max41

min40

max……Liquid Limit

Characteristics of fraction passing 0.425 mm (No. 40)

36 min36

min36

min36

min35

max35

max35

max35

max10

max25

max15

max0.075 (No. 200)

……………………51

min50

max30

max0.425 (No. 40)

…………………………50

max2.00 mm (No. 10)

Sieve Analysis, % passing

A 7 5 A 76

A-2-7A-2-6A-2-5A-2-4A-1-bA-1-a

52

Note (1): Plasticity index of A-7-5 subgroup is equal to or less than the LL - 30. Plasticity index of A-7-6 subgroup is greater than LL - 30

fair to poorexcellent to goodGeneral rating as a subgrade

clayey soilssilty soilssilty or clayey gravel and sandfine sand

stone fragments,

gravel and sand

Usual types of significant constituent materials

11 min111 min

10 max

10 max

11 min

11 min

10 max

10 max

N.P.6 maxPlasticity Index


27

Proctor Moisture-Density

Compaction improves engineering properties of soils

• Minimizes settlements in road surface.

• Increases soil density - strength.

• Increases bearing capacity.

• Helps control volume change.

Amount of moisture in the soil affects compaction.


Developed by R.R. Proctor in 1930’s:

• Engineer for Los Angeles County.


• Earth dams.

Consists of rammer that falls vertically onto soil that is placed in a cylindrical mold.

Different procedures for different soil gradations.

Two specified compaction efforts:

St d d


• Standard.

• Modified.

28

Standard

• Three layers Modified

• Five layers


y

• 12 inch drop

• 4.5 lb. Rammer

• 12,400 ft-lb/ft3

• 600kN-m/m3

Five layers

• 18 inch drop

• 10 lb. Rammer

• 56,000 ft-lb/ft3

• 2700kN-m/m3


Using specific amount of compaction effort, density and moisture content varies.


Test used to determine optimum moisture content to get maximum soil density for a level of compaction energy.

• Standard Proctor is minimum acceptable.

• Modified is preferred


29





30


2100

2300

1300

1500

1700

1900

Dry

Den

sity

(k

gs/m

3)


1100

0 5 10 15 20 25 30 35 40

Gravimetric Moisture Content(%)

GranularBase Sand Clay Till Silt Clay

Developed in late 1920’s.

Used by highway departments for evaluation of all road

California Bearing Ratio (CBR)

soils and granular.

Bearing ratio of soils determines amount of load that soil can carry.

Saskatchewan Highways uses bearing ratio for pavement design.

Higher soil bearing ratio = thinner pavement, base, or


Higher soil bearing ratio thinner pavement, base, or sub-base layers = less $$$.

31

Soil sample prepared according to Proctor compaction procedure.

California Bearing Ratio (CBR) Soaked Swell Test

Sample is soaked for 4 days.

Swelling during soaking is measured.


California Bearing Ratio (CBR) Soaked Swell Test


32

California Bearing Ratio (CBR) Soaked Strength Test

Determined by pushing a cylindrical piston with an area of 1935 mm2 into a prepared soil sample at a standard

f 1 3 / i 2 0 / irate of 1.3 mm/min to 2.0 mm/min.

Applied pressure required to maintain the penetration rate is recorded at 2.5mm intervals up to a penetration depth of 12.5mm.

Measures the “relative” shearing resistance of soil.

Does not directly relate to field loading conditions, but


it does provide a repeatable relative measure of soil strength.



33



P


Penetration(mm)

Pressure(MPa)

10.4

15.9

Crushed Rock CBR

Surcharge49.6 mm

200

mm

15 m

m

Compacted Soaked Sample

2.5

7.6 13.15.0

10.2

6.9


15.9

152.4 mm dia.

1 12.7 17.90.

34

CBR is calculated as ratio of pressure at a given penetration increment during the soil test to that of a


p gstandard high-quality crushed rock.

npenetratio 12.5mm to2.5mm @rock Crushed

npenetratio 12.5mm to2.5mm @ Soil

F

FCBR


SDHT GI-CBR Correlation

12

14

y = -3E-05x5

+ 0.002x4

- 0.0546x3

+ 0.7184x2

- 4.9707x + 20.172

R2

= 0.9994

4

6

8

10

CB

R


0

2

0 2 4 6 8 10 12 14 16 18 20

Group Index

35

SMHI Pavement Structural Design

Conventional Flexible Pavement Structural Design

69

Substructure Moisture 20 yrs+Field Measurements

Per

mit

tivi

ty

WB10.0

10.5

11.0

11.5

12.0

28.00029.00030.00031.00032.00033.00034.00035.00036.00037.00038.00039.000

Die

lect

ric

P

Chainage (km)

EB

7.0

7.5

8.0

8.5

9.0

9.5

Per

mit

tivi

ty

SB

20 0

22.0

24.0

26.0

28.0

30.0


35.000 36.000 37.000 38.000 39.000 40.000 41.000 42.000 43.000 44.000

Die

lect

ric

P

Chainage (km)

NB

10.0

12.0

14.0

16.0

18.0

20.0

36

Moisture Induced Sub-Structural Failure


71

DiscussionDon’t hold back. You have a great deal tocontribute. Join in the spirit and camaraderief ki hi i i h Thof making something exciting happen. There

are many ways and places to make a living.We must do that, but each of us also desires toaccomplish something more exhilarating andcreate lasting value through our efforts.


introduction to road soil characterization - u of s ... course notes-march 17-19 201… ·...

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