PHYSICAL PROPERTIES AND ENGINEERING CLASSIFICATION OF SOIL

CHAPTER 1

§1 Physical properties and classification of soil

§1.1 formation of soil§1.2 tri-phase components of soil§1.3 soil fabric§1.4 phase relations §1.5 physical states and Index§1.6 soil compaction §1.7 soil classification

§1.1 formation of soil

Soil formed by rock in different condition after weathering.

transportation 、 deposit

formation processformation condition

physical or mechanical properties

rock

earth

soil

earth

influence

weathering

Soil Formation

Parent Rock

Residual soil

~ in situ weathering (byphysical & chemicalagents) of parent rock

Transported soil

~ weathered andtransported far away

by wind, water and ice.

Residual Soils

Formed by in situ weathering of parent rock

Soil grain sizes vary in large range

Mineralogy is dependent of parentrock

Transported Soils

Transported by:

wind

sea (salt water)

lake (fresh water)

river

ice

Special name:

“Aeolian”

“Marine”

“Lacustrine”

“Alluvial”

“Glacial”

§1.2 tri-phase components of soil

vapor phasesolid phase liquid phase+ +

composing soil framework, final effect

significant effect

Soil mass

§1 Physical properties and classification of soil

secondary effect

solid grain

physical state &mechanical characteristics

grading级配

mineral

components

grain shape

1.2.1 solid phase

Minerals

• Minerals are crystalline materials and make up the solids constituent of a soil. The mineral particles of fine-grained soils are platy. Minerals are classified according to chemical composition and structure.

• Original mineral ： quartz, feldspar, isinglass, hornblende and pyroxene.

• Secondary mineral ： consists mainly of clay mineral

Clay Minerals

1. Sizes smaller than 2 m2. Tiny flakes or needles inshape3. Soil has plasticity only ifit contains clay minerals

Clay minerals• Final product of weathering• Consisting of two distinct structural

units.hydroxyl or

oxygen

silicon

0.26 nm

Silicon tetrahedron

oxygen

aluminium ormagnesium

0.29 nm

Aluminium Octahedron

hexagonalhole

Tetrahedral & OctahedralSheets

For simplicity, we represent silica tetrahedral sheet by:

Si

and alumina octahedral sheet by:

Al

Different Clay Minerals

Different combinations of tetrahedral and octahedralsheets form different clay minerals:

1:1 Clay Mineral (e.g., kaolinite, halloysite):

Different Clay Minerals

Different combinations of tetrahedral and octahedralsheets form different clay minerals:

2:1 Clay Mineral (e.g., montmorillonite, illite)

Kaoliniteused in paints, paper and in pottery and pharmaceuticalindustries

(OH)8Al4Si4O10

AlSi

Typically70-100layers

joined by strong H-bondno easy separation

Al

Si

Al

Si

Al

Si

0.72 nm

joined by oxygensharing

Montmorillonite

also called smectite; expands on contact with water

Si

Al

Si

Si0.96 nmAl

Si

Si

Al

Si

easily separatedby water

joined by weakvan der Waal’s bond

Montmorillonite

Ahighly reactive (expansive) clay

swells on contact with water

high affinity to water

(OH)4Al4Si8O20.nH2O

Bentonite montmorillonite family y

used as drilling mud, in slurry trench walls,stopping leaks

Montmorillonite

Montmorillonites have very high specific surface,cation exchange capacity, and affinity to water.They form reactive clays.

Montmorillonites have very high liquid limit (100+),plasticity index and activity (1-7).

Bentonite (a form of Montmorillonite) is frequently used asdrilling mud.

Si

Illite

Si

Al

joined by K+ ions

0.96 nmfit into the hexagonalholes in Si-sheet

Si

Al

Si

Si

Al

Si

Summary

Others Clay Minerals

Chlorite绿泥石 A2:1:1 mineral.

Halloysite埃洛石 kaolinite family

Si Al Al or Mg tubular structure

Vermiculite蛭石 montmorillonite family

swelling clay

Attapulgite凹凸棒石 chain structure

needle-like appearance

Shapes of soil particles

Soil Grain Size

Granular soils orNon-cohesive soils

Cohesivesoils

BoulderClay Sand GravelSilt

0.002 200

Cobble

634.750.075

Grain size (mm)

Fine grainsoils

Coarse grainsoils

Grain Size Distribution (GSD)

Determination of GSD:

• In coarse grain soils …... By sieve analysis

In fine grain soils …... By hydrometer analysis

hydrometer

stack of sieves

sieve shaker

soil/water suspension

Sieve Analysis Hydrometer Analysis

Grain size distribution curve

D

Cc and Cu

Cu : Coefficient of uniformity

D60

D10Cu

Cc :Coefficient of curvature230

(D60D10)Cc

D60 is the diameter of the soil particles for which 60% of the particles are finer.

Well or Poorly Graded Soils

Well Graded Soils

Wide range of grain sizes

Gravels: Cc = 1-3 & Cu >4

Sands: Cc = 1-3 & Cu >6

Poorly Graded Soils

Two special cases:

(a) Uniform soils – grains of same size

(b) Gap graded soils – no grains in aspecific size range

Well graded

Poorly graded

Water in soil is the liquid phase, and its types and quantities have important influence upon the state and porosities of soil.

1.2.2 liquid phase

crystal water : mineral inner water

combined water: water absorbed on soil grain surface

free water: water out of electric field gravitation

soil ice: free water freeze

Absorbed water

• close arrange 、 powerful directing property• density>1g/cm3• freezing point is minus dozens degrees• having solid character• temperature>100°C can vapor

powerful absorbed water

• outside powerful combined water ，inside electric-field attractive force• can move in the effect of outside force• not remove as a result of gravitational force ， having viscidity

feeble absorbed water

free water

bulk water

capillary water

under gravitation, can flow in soil

• exist between solid and gas • under gravitation and surface tension, can move on soil grain interspace freely

3. soil gas

free gas ： connect atmosphere ， no great effect on soil properties

closed gas ： enhance soil elasticity ； block seepage flow channel

1.2.3 Vapor phase

Clay Fabric

face-to-face contact

Dispersed

edge-to-face contact

Flocculated

§1.3 Soil fabric

coarse-grained soil fabric

•forces among particles:

• mineral component:

gravitation， capillary force

point to point contact 、 point to plane contact

original mineral

§1.4 Phase Relations

Soil is a three phase system:

Solids

Water

Air

Objectives

To compute the masses (or weights) andvolumes of the three different phases in soil

airVa Ma=0

VvM = mass (kg, Mg)

Mt

water MwVw

Vt

W =weight (kN)V = volume (m3)s = soil grains

soilVs Ms

w = watera = airv = voidst = total

Soil Water (Moisture) Content, w (%)

A measure of water present in soil.

air

water

Ma=0

Mw

Va

Vw

VvMW

M S

X 100%w =

MtVt

soilVs MsExpressed as percentage.

Range = 0 ~ >> 100%.

Phase Diagram

Soil Void Ratio, e [-]

A measure of the void volume in soil.

V V

V S

air

water

Ma=0

Mw

Va

Vw

Vve=

MtVt

soilVs Ms

Range = 0.3 ~ > 3

Phase Diagram

Soil Porosity, n [-] or %

Another measure of soil void volume

n= VV

Vt airVa Ma=0

Vv

water Mw

Mt

Vw

Vt

Theoretical range: 0 – 100%soilVs Ms

Degree of Saturation, S %

The percentage of the void volume filled by water.

VW

VV

X 100%air

water

Ma=0

Mw

Va

Vw

VvS=

Range: 0 – 100%

MtVt

Dry

soilVs Ms

Phase Diagram

Saturated

A Simple Example

When

air

water

soil

Vs = Vv and

Va = Vw

e=?

S= ?

n=?

Bulk Density, b[kg/m3, Mg/m3]

Density of the soil in the current state.

Vv

MtVt

Units:

b =

Mg/m3,

Mt

Vt

kg/m3

air

water

soil

Va

Vw

Vs

Ma=0

Mw

Ms

Phase Diagram

Special cases of bulk density -1 1

Dry density (soil voids are filled with air).

airVa Ma=0

Vv

d =?

MtVt

soilVs Ms

Phase Diagram

Special cases of bulk density -2 2

Saturated density (soil voids are filled with water).

waterMwVw

Vv

sat =?

MtVt

soilVs Ms

Phase Diagram

Specific Gravity, Gs [-]

Ratio of solid density and water density

s

wGs

Typical values for soil(inorganic) solids:

air

water w

soil Gsw

Gs = 2.5 – 2.8

Phase Diagram

Useful Equations-1

If we set Vs = 1e

V v air

See

V

S

V w

water Sewt

soil1 Gsw

s

w

M

M

Phase Diagram

Useful Equations-2

If we set Vs = 1

See

MW

M S

w air

water Sew

n soil1 Gsw

VV

Vt

Phase Diagram

Useful Equations-3

Mt

Vt

b

Mt(S 1)

Vt

sat

air

waterSee

Sew

Mt(S 0 )

Vt

d soil1 Gsw

Phase Diagram

Density and Unit Weight

Bulk, saturated, dry and submerged unit weights ()

= g

9.81 m/s2N/m3

kN/m3kg/m3

Mg/m3

A Gentle Reminder

Try not to memorize the equations. Understand thedefinitions, and develop the relations from the phasediagram;

Assume GS (2.6-2.8) if the soil is natural and inorganic(unless you are required to calculate it!);

Do not mix densities and unit weights;

Soil grains are incompressible. Their mass (Ms) andvolume ( (Vs) remain the same at any void ratio;Phase relations do not reflect soil grain sizedistributions

Example 1

A saturated soil has amoisture content of38.0% and a specific air

waterSee

Sew

gravity of solids of2.73. Compute thevoid ratio, porosityand unit weight

soil1(kN/m3) of this soil. Gsw

Phase Diagram

Example 2

On a construction site, the soil bulk

airdensity and water content havebeen measured as = 1.76Mg/m3, w = 10%. In the

waterSee

Sewsubsurface survey report, youneed to report:

d (dry density)

1.

soil12.3 3.4.5.

e (void ratio)n (porosity)S (degree of saturation)

sat(saturated density)

Gsw

Phase Diagram

Exercise

Prove: d= b/(1+w)

Vv

MtVt

air

water

soil

Va

Vw

Vs

Ma=0

Mw

Ms

Relative Density (Dr)ASTM D4253 and D4254

Indication of how densely the grains arepacked in a coarse grain soil.

0

Loosest

100%

Densest

Dr e

emin

emax

emax

Also known as density index (ID) ).

§1.5 physical states and Index

Consistency y of g granular soils:Judged by relative density

Relative Density (%)

0-15

15-35

35-65

65-85

85-100

Consistency Term

Very loose

Loose

Medium dense

Dense

Very dense

Fines in Soil

Fines: Soil solids passing #200 Sieve (< 74 m)

Consistency of fines:

Very soft: exudes between fingers

Soft: very easy to mould and sticks to hand

Firm: moulds easily with moderate pressure

Very firm: moulds only with consideratepressure

Hard: will not mould under pressure in the hand

Crumbly: breaks up into crumps

Atterberg Limits – for classificationof fines

A set of border line soil water contents thatseparate the different states of a fine grainedsoil

Liquidlimit

Plasticlimit

0 water content

liquidsemi-solid

Shrinkagelimit

brittle-solid

plastic

Atterberg Limits – 3 components

Liquid Limit (wL or LL):

Clay flows like liquid when w > LL

Plastic Limit (wP or PL):Lowest water content where the clay is still plastic

Shrinkage Limit (wS or SL):

At w<SL, no volume reduction on drying

Measure Liquid Limit (LL)

Measure Plastic Limit (PL)

Plasticity Index (PI)

Range of water content over which the soilremains plastic

Plasticity Index = Liquid Limit – Plastic Limit

Liquidlimit

Shrinkagelimit

Plasticlimit

0water content

plastic

Plasticity Index PI = LL-PL:Indicator of soil plasticity

PI

0 0-3 3

3-15

15-30

>30

Dry strength

Very low

Slight

Medium

High

Classification

Non plastic

Slightly plastic

Medium plastic

Highly plastic

Liquidity Index (IL)

I L wn

LL

PL

PL

Wn = natural soil moisture content

LLShrinkage PL0w, %

limit

PI

IL : Indicator of soil liquefiability

IL

<0

0 <IL < 1

IL > 1

wn

wn < PL

PL < wn < LL

wn > LL

Soil condition

Non-plastic, non-liquefiable

Plastic, non-liquefiable

Liquefiable

This is a soil profile from

a site in Gloucester,

Ontario. The Soil can

be divided into two

layers: layer 1: A, B,

C, D and layer 2: E.

1. What can we conclude

from the inspection of

the soil profile?

2. Estimate the liquidity

index for Layer 2.

Compaction of Earth WorksRef: Coduto Chapter 6

1

§1.6 soil compaction

What is compaction?

A simple ground improvement technique,where the soil is densified through externalcompaction effort.

Compactioneffort

+ water =

2

Compaction: reduce air and wateri in soil il

3

Field CompactionDifferent types of rollers (clockwisefrom right):

Vibratory roller

Smooth-wheel roller

Pneumatic rubber tired roller

Sheep-foot roller

4

Field CompactionVibrating Plates

5

for compacting very small areaseffective for granular soils

Field CompactionSmooth Wheeled Roller

•

•

Compacts effectivelyonly to 200-300 mm;Place the soil inshallow layers (lifts)

6

Field CompactionImpact Roller

Provides deeper(2-3m)compaction. e.g.,air field

7

Field CompactionSheep-foot Roller

Provides kneading actionVery effective on clays

8

Advantage of sheep- -foot roller incompaction of clay liners

9

Pounder (Tamper)

Dynamic Co ompaction

Suitable for granular soils, land fillsand karst terrain with sink holes.

solution cavities inlimestone

Crater created by the impact(to be backfilled)

10

11

d)

dens

ity

( D

ryd

Compaction Curve

Increasing compactionenergy results in:

• Lower optimum

E2 (>E1)water content

• Higher maximum drydensity

E1

Water content

12

Compaction Curve

Gs w

1 wGs /S d

b

1 w d

13

Effect of moisture content duringcompaction on soil fabric in clays

14

Laboratory Compaction Test

Standard Proctor:

• 3 layers

• 25 blows per layer

• 2.7 kg hammer

• 300 mm drop

Modified Proctor:

• 5 layers

• 25 blows per layer

• 4.9 kg hammer

• 450 mm drop

1000 ml compaction mould (1.0 x 10-3 m3)

15

Laboratory yCompaction

Test

16

Compaction Control

17

Measure density and water contentin field

18

Nuclear meter

19

20

Compaction Specifications

– Design specifications

• For sands and gravels: relative density (ID)• For fine grained soils, relative compaction ( R) and soilmoisture content

– Prescriptive specifications – contractor builds a test pad toestablish compaction effort required to achieve the end result ,including

• the compaction equipment

• thickness of soil layers

• number of travels

21

• soil water content, , etc.

Shrink and Swell from Cut to FillMake sure the definition is clear to all parties on the job;Cut and fill specifications must be careful determinedShrinkage factor is sensitive to errors – it could lead to serious

economic problems during a job

22

Shrinkage Factor

1)100%SF ( d fill

dcut

• Make sure the definition is clear to all parties on thejob

• Cut and fill specifications must be careful determined

• SF calculations are sensitive to errors – it could leadto serious economic problems during a job

23

United Soil Classification System(USCS)

•Developed by A. Casagrande in 1948

•ASTM Standard D2487

•Commonly used by geotechnical engineers

•Require two sets of tests for soil classification, i.e.

•Gradation (sieve and hydrometer) tests

•Atterberg limits (PL, LL) tests

§1.7 soil classification

USCS Symbols

% of fines

f fine grain soilscoarse grain soils

0 5 12 50 100

XA

YB

e.g., CH, ML

XY

e.g., SM, GC

B: Plasticity

e.g., GP

SW

XA-XY

e.g., SP-SC, GW-GM

X: Coarse

G = Gravel

S = Sands

(Sieve analysis)

Y: Fines

M = Silts

C = Clays

(C’s Chart)

A: Gradation

W = well graded

P = poorlygraded

(Cc and Cu)

H: LL > 50

L: LL < 50

(C’s Chart)

Casagrande’s s Plasticity Chart

U-line: IP = 0.9(wL – 8)

A-line: IP = 0.73 (wL – 20)

Fine grained soils (> 50% passing #200 sieve)Coduto pp. 175

Coarse grained soils (< 50% passing #200 sieve)

Codutopp. 178

Other considerations -1

Other considerations -2

Other considerations -3

Other considerations -4

Applicability and Limitations

“ It is not possible to classify all soils into arelatively small number of groups suchthat the relation of each soil to the manydivergent problems of applied soilmechanics will be adequately addressed.”

Arthur Casagrade 1948