soil machanics_lecture (2)_soil classification

PBW N302Credit HoursCredit Hours

CEM/WEE/STE

Dr. Asmaa ModdatherSoil Mechanics and Foundations

Faculty of Engineering – Cairo University

FALL 2012FALL 2012

SOIL CLASSIFICATIONSOIL CLASSIFICATION

Dr. Asmaa Moddather – PBW N302 – Fall 2012

S il Cl ifi tiSoil Classification

• Soil classification: is the arrangement of different soils with similar

ti i t th t fl t il’ h i l d h i lproperties into groups that reflects soil’s physical and mechanical

properties.

• The purpose of soil classification is to provide the geotechnical engineerp p p g g

with a way to predict the behavior of the soil for engineering projects.

• Soils are usually classified into various types such as:

Cohesion: cohesive soils (silt, clay)/non‐cohesive soils (sand, gravel).

Grain size: fine‐grained soils (silt, clay)/coarse‐grained soils

g ( , y)/ g

(sand, gravel).

C i d ilCoarse‐grained soils

Angular Subangular Subrounded

Rounded Well rounded

Fi i d ilFine‐grained soils

PlateClayClay

G i Si A l iGrain Size Analysis

• Laboratory testing:

o Sieve analysis tests: for coarse‐grained soil

o Hydrometer tests: for fine‐grained soil

• A ‘‘grain size distribution curve’’ is obtainedg ain si e dist ibution cu ve s obta ed

from these tests

Si A l i T tSieve Analysis Test

Set of sievesSieve shaker

Soil Samplew

Sieve Analysis Testw1

• The usual procedure is to use a system of

i h i diff t h i t k d

w sieves having different mesh sizes, stacked on

top of each other, with the coarsest mesh on

top and the finest mesh at the bottom. After

shaking the assembly of sieves, by hand or bySievesw7

w g y , y y

a shaking machine, each sieve will contain

th ti l l th it h i d

the particles larger than its mesh size, and

smaller than the mesh size of all the sievesw10

wabove it.

Dr. Asmaa Moddather – PBW N302 – Fall 2012w12w13 Pan

Si A l i T tSieve Analysis Test

1043/8 in¾ in1 ½ in3 inSieve No.

24.759.5193875Particle size (mm)

PAN200140100604020Sieve No.

0.0750.1060.150.250.4250.85Particle size 75554 55(mm)

Si A l i T tSoil Sample

Sieve Analysis Test

WW + W

Soil Sample

Weight of sample = W gm SievW2

W1 + W2

2001401 ½ in3 inSieve No.

0.0750.106‐‐‐‐‐‐‐‐‐‐‐‐3875Particle size (mm)

w12w11‐‐‐‐‐‐‐‐‐‐‐‐w2w1Weight Retained on each sieve (gm)

w1 + ‐‐‐+ w12

w1 + ‐‐‐+ w11

‐‐‐‐‐‐‐‐‐‐‐‐w1 + w2w1Total weight Retained (gm)

{ }x100/W{ }x100/W‐‐‐‐‐‐‐‐‐‐‐‐{ }x100/W{ }x100/W% Retained

100 ‐100 ‐‐‐‐‐‐‐‐‐‐‐‐‐100 ‐100 ‐%Passing

E lExample

P6 iSi N

Weight of sample = 250 gm sieves

Pan20010060201043 inSieve No.

‐‐0.0750.150.250.852.04.7575Particle size (mm)(mm)

133048513548250.0

Weight Retained on

h i 133048513548250.0each sieve (gm)

Total weight 25023720715910873250.0

Total weight Retained (gm)

94.882.863.643.229.210.00.0% Retained

5.217.236.456.870.890.0100.0%Passing

Dr. Asmaa Moddather – PBW N302 – Fall 2012Hydrometer test

H d t T tHydrometer Test

Hydrometer

H d t T tHydrometer Test

• Indirect method of measurement.

• Soil sample is mixed with water and additives in agraduated cylinder to form a soil suspension.g y p

• Larger (heavier) particles settles faster than smaller(lighter) particles.

• The density of the suspension is measured with ahydrometer at determined time intervals.

• Computations are based on Stokes‘ formula.

G i Si Di t ib ti CGrain Size Distribution Curvesieves hydrometer

20010060201043 inSieve No.

.010.020.040.0750.150.250.852.04.7575Particle size (mm)

0.51.83.05.217.236.456.870.890.0100.0%Passing 53573 4579g

6070809

304050

% Pass

010203

Arithmetic scale

020406080Particle size (mm)

G i Si Di t ib ti CGrain Size Distribution Curvesieves hydrometer

20010060201043 inSieve No.

.010.020.040.0750.150.250.852.04.7575Particle size (mm)

0.51.83.05.217.236.456.870.890.0100.0%Passing 53573 4579g

75; 100

4.75; 9090100

2; 70.8

0 85; 56 86070809

0.85; 56.8

0.25; 36.4

304050

% Pass

0.15; 17.2

0.075; 5.20.04; 3 0.02; 1.8 0.01; 0.5010203

Semi‐log scale

0.0010.010.1110Particle size (mm)

S i l lSemi‐log scale paper100

assing

40% Pa

G i Si Di t ib tiGrain Size Distribution

%Passing = 60

Passing

%Passing 60

%Passing = 30

20%Passing = 10

0.0010.010.1110Particle size (mm) D

D30100

Particle size (mm) D60 D10

• D60 is the diameter of the particle at 60% passing on the grain size distribution

curvecurve.

• D i th di t f th ti l t % i th i i di t ib ti• D30 is the diameter of the particle at 30% passing on the grain size distribution

curve.

• D10 is the diameter of the particle at 10% passing on the grain size distribution

curve. “effective grain size”

• Coefficient of Uniformity (Cu) = D60/D10

Dr. Asmaa Moddather – PBW N302 – Fall 2012• Coefficient of Curvature (Cc) = (D30)2/(D60D10) = 1 ‐ 3

• W ll d d d 6• Well graded sand cu > 6.0, cc = 1‐3

• Well graded gravel cu > 4.0, cc = 1‐3

W ll d dPoorly graded

Well graded Uniformly graded

oo y g aded

Gap graded

% Passin

0.0010.010.1110Particle size

G i Si Di t ib tiGrain Size DistributionD60 = 1.0 mm, D30 = 0.2 mm, D10 = 0.095 mm

Cu = 1.0/0.095 = 10.5, Cc = (0.2)2/(1.0 x 0.095) = 0.42

%Passing = 60

% Passi

%Passing 30

30%Passing = 30

%Passing 10

10%Passing = 10

0.0010.010.1110Particle size (mm) D60

C i t f C h i S ilConsistency of Cohesive Soils

• For fine‐grained soils (silt, clay), the consistency is an

important property.

• It determines whether the soil can easily be handled byIt determines whether the soil can easily be handled, by

soil moving equipment, or by hand.

• The consistency is often very much dependent on the

f i h il Thi i d b hamount of water in the soil. This is expressed by the water

content w.

C i t f C h i S ilConsistency of Cohesive Soils

• When the water content is very low (as in a very dry clay) the soil can be

tiff l t lik t It i th id t b i th lid t tvery stiff, almost like a stone. It is then said to be in the solid state.

• Adding water, for instance if the clay is flooded by rain, may make the

clay plastic, and for higher water contents the clay may even becomey p , g y y

almost liquid.

• In order to distinguish between these states (solid, plastic and liquid)

three standard tests have been agreed upon, that indicate the

consistency limits. They are denoted as “the Atterberg limits”.

Att b (C i t ) Li itAtterberg (Consistency) Limits

Adding waterVolume

Liquid

Plastic

Liquidlimit

Shrinkage

limitDry soil

S SWater content

Solid state Semi‐solid state Plastic state Liquid state

Att b (C i t ) Li itAtterberg (Consistency) Limits

•Li id li it (L L ) i th t iti f th li id t t•Liquid limit (L.L., wL): is the transition from the liquid state

to the plastic state. It represents the lowest water content atp p

which the soil behavior is still mainly liquid.

•Plastic limit (P.L., wP): is the transition from the plastic state

to the semi‐solid stateto the semi solid state.

•Shrinkage limit (Sh.L., wSh): is the transition from the semi‐

solid state to the solid state.

•Pl i i i d (PI I )•Plasticity index (PI, Ip) = wL‐ wP

•These limits are obtained using laboratory tests.

Li id Li it T tLiquid Limit Test

Liquid limit device

Dr. Asmaa Moddather – PBW N302 – Fall 2012Grooving tool

•The liquid limit is the value of the water content for which a standard

V h d t i th il ill j t l ( i h) ft dV‐shaped groove cut in the soil, will just close (0.5 inch) after 25 drops.

Water content

No. of blows

Log No. of blows

Pl ti Li it T tPlastic Limit Test

•Plastic limit is defined as the water content at which the clay can just be

ll d t th d f di trolled to threads of 3 mm diameter.

• Very wet clay can be rolled into very thin threads.

• Dry clay will break when rolling thick threads.

Sh i k Li it T tShrinkage Limit Test

•Put soil sample in oven until it is completely dry, and get its

( )weight (ws).

•Shrinkage limit is the water content of this sample if it is

d h h lsaturated with water at the same volume.

• Measure the total volume of the oven‐dried sample (vT):

oS b i h l i f i l i i i h ffioSubmerging the sample in water after insulating it with paraffin

o Submerging the sample in mercury. (Gs,mercury = 13.6)

Sh i k Li it T tShrinkage Limit Test

vs = ws/(Gsγw)

ShrinkagelimitDry soil

v = v – v

vv = vT – vs

v vw wwww = vv γw vT

S SSh.L. = ww/wswsvs wsvs

C i t I d f C h i S ilConsistency Index of Cohesive Soils

L wwCI −=

PL ww −

Type of SoilCI

Very soft0 – 0 5 Very soft0 0.5

Soft0.5 – 0.625

Medium stiff0.625 – 0.75 Medium stiff0.625 0.75

Stiff0.75 – 1.00

Very stiff1.00 < Very stiff.00(w > wSh)

Hard1.00 <( )

(w < wSh)

E lExample

•The following table shows the parameters determined for different

cohesive soil samples for these soils determine Find the consistencycohesive soil samples, for these soils determine Find the consistency

index and comment on its indication.

indicationCIwSh (%)wP (%)wL (%)w (%)Soil

M. stiff0.7010406046A

V. stiff1.109154512B

V. soft0.2025109C

Type of SoilCI

Very soft0 – 0.5

S f 6 Soft0.5 – 0.625

Medium stiff0.625 – 0.75

Stiff0.75 – 1.00

Very stiff1.00 < – (w > wSh)

Hard1.00 < ‐ (w < wSh)

R l ti D it f C G i d S ilRelative Density of Coarse‐Grained Soil

Loose Densee eminemax min

• emax is the maximum possible void ratio loosest packing

A hi d b f ll i th il i t t i b l tti thAchieved by carefully pouring the soil into a container, or by letting the

material subside under water, avoiding all disturbance.

• emin is the minimum possible void ratio densest packing

Obtained by strong vibration of a sample.

R l ti D it f C G i d S ilRelative Density of Coarse Grained Soil

• emax is the maximum possible void ratio.

•The loosest packing can be achieved by carefully pouring the soil into a

container, or by letting the material subside under water, avoiding all

disturbance.

• i th i i ibl id ti• emin is the minimum possible void ratio.

•The densest packing of the soil can be obtained by strong vibration of a

sample.

R l ti D it f C G i d S ilRelative Density of Coarse Grained Soil

100xee(%)D actmaxr

minmaxr −

Type of SoilDr (%)

Very loose0 – 15

Loose15 – 35

Medium dense35 ‐ 65

Dense65 – 85

Very dense85 ‐ 100

S il Cl ifi tiSoil Classification

• There are many different soil classification systems in

o MIT classification systemo MIT classification system.

o Unified Soil Classification System (USCS).

MIT Cl ifi ti S tMIT Classification System

• Soil is classified based on grain size.

• Th i i i d t i d b f i i i l i• The grain size is determined by performing a grain size analysis.

Sieve analysis Hydrometer test

Gravel Sand Silt ClayBoulders

C M F C M F C M F0 02 6

60 mm 2 mm 0.06 mm 0.002 mm20 6 0.6 0.2 0.02 0.006

C: CoarseM: Medium

F: Fine

G i Si Di t ib ti CGrain Size Distribution Curve

G l S d Silt Cl60 mm 2 mm 0.06 mm 0.002 mm

Gravel Sand Silt Clay

% Passi

G i Si Di t ib ti CGrain Size Distribution Curve

% B ld % P i 6 %% Boulder = 100 ‐ % Passing 60mm = 100 – 97 = 3%

% Gravel = % Passing 60mm ‐ % Passing 2mm = 97 – 70.8 = 26.2 %

% Sand = % Passing 2mm ‐ % Passing 0.06mm = 70.8 – 6.0 = 64.8 %

% Silt = % Passing 0.06 mm ‐ % Passing 0.002 mm = 6.0 – 0.0 = 6.0 %

G l S d Sil Cl60 mm 2 mm 0.06 mm 0.002 mm

% Silt % Passing 0.06 mm % Passing 0.002 mm 6.0 0.0 6.0 %

% Clay = % Passing 0.002mm = 0.0 %

8090100

Gravel Sand Silt Clay

50607080

Passing

10203040

MIT Cl ifi ti S tMIT Classification System

• Soil Group Name:

o 50 – 35 % : ando 50 – 35 % : and

o 35 – 15 % : adjective

%o 15 – 5 % : some

o < 5 % : trace of

% Boulder = 3.0%

% Gravel = 27.2%

% Sand = 65.8%

% Silt = 5.0%

% Clay = 0.0%

ifi d il l ifi iUnified Soil Classification System (USCS)

• Soil is classified based on:

o Grain sizeo Grain size

o Gradation

o Soil Plasticityo Soil Plasticity

• Information needed:

G i i di ib io Grain size distribution curve:

cu, cc% Passing sieve No. 4 (4.75 mm)

% Passing sieve No. 200 (0.075 mm)

o Atterberg limits:

• Soil is identified by a Group Symbol

o Grain size:o Grain size:

Gravel G

Sand SSand S

Silt M

Cl CClay C

o Gradation:

Well graded W

Poorly graded P

o Plasticity

L.L. < 50% (low plasticity) L

L.L. > 50% (high plasticity) H

• % Fine‐grained soil = % Passing sieve No. 200

• % C i d il % P i i N ined soil

Gravel

• % Coarse‐grained soil = 100 ‐ % Passing sieve No. 200

or = % Retained on sieve No. 200 Sieve No. 4

rse‐grai

• % Gravel = 100 ‐ % Passing sieve No. 4Sieve No. 200

• % S d % P i i N % P i i N e‐graine

Silt & Clay

• % Sand = % Passing sieve No. 4 ‐ % Passing sieve No. 200

USCS S T blUSCS Summary Table

Use plasticity chart to determine M or C

Use Plasticity Chart oo

bbbbbbbbbbbbboo

ifi d il l ifi iUnified Soil Classification System (USCS)% Passing sieve No. 200

< 50% > 50%< 50% 5

Fine‐grained soilCoarse‐grained soil

Use Plasticity

Chart (A‐line)

LL & PI

CH, CL

ML, MH

Pl ti it Ch t (A Li )Plasticity Chart (A‐Line)

(%) CH

CL Ip = 0.73(wL-20)

10MLCL-ML ML

0 10 20 30 40 50 60 70 80 90 100

Liquid Limit (%)

< 50% > 50%< 50% 5

% Passing sieve No. 4

G lS d GravelSand

% Passing sieve No. 200%Gravel > % Sand%Sand > % Gravel

< 5% 5% ‐ 12% > 12%

Care for gradation Care for finesDual symbolCare for gradation

Inspect cu, cc

Care for fines

Inspect L.L., P.I., A‐line

SW‐SC

SP‐SM

Dual symbol

SW, SP

GW, GP

SC, SM

GC, GMGW‐GM

GP‐GC

< 50% > 50%< 50% 5

Use Plasticity Chart

G lS d(A‐line)

LL & PI

GravelSand

< 5% 5% ‐ 12% > 12%

Care for gradation Care for finesDual symbol

CH, CL

Care for gradation

SW, SP

Care for fines

SC, SM

SW‐SC

SP‐SM

Dual symbol

ML, MHGW, GP GC, GMGW‐GM

GP‐GC

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