soil machanics_lecture (2)_soil classification
DESCRIPTION
How to classify soil using the MIT and USC systems accompanied by solved examplesTRANSCRIPT
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
g ( , y)/ g
(sand, gravel).
C i d ilCoarse‐grained soils
Angular Subangular Subrounded
Rounded Well rounded
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Fi i d ilFine‐grained soils
PlateClayClay
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Si A l i T tSieve Analysis Test
f i
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Set of sievesSieve shaker
Soil Samplew
w
Sieve Analysis Testw1
w2
• The usual procedure is to use a system of
i h i diff t h i t k d
w3
w sieves having different mesh sizes, stacked on
top of each other, with the coarsest mesh on
w4
w5
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
w8
w9
the particles larger than its mesh size, and
smaller than the mesh size of all the sievesw10
wabove it.
w10
w11
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)
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Si A l i T tSoil Sample
Sieve Analysis Test
ves
W1
WW + W
Soil Sample
Weight of sample = W gm SievW2
W3
W1 + W2
W3
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
90100
6070809
sing
304050
% Pass
010203
Arithmetic scale
Dr. Asmaa Moddather – PBW N302 – Fall 2012
020406080Particle size (mm)
scale
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
sing
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
0.0010.010.1110Particle size (mm)
100
S i l lSemi‐log scale paper100
8
90
100
70
80
50
60
assing
30
40% Pa
10
20
30
0
10
100
Dr. Asmaa Moddather – PBW N302 – Fall 2012
0.0010.010.1110Particle size (mm)
100
G i Si Di t ib tiGrain Size Distribution
90
100
70
80
%Passing = 60
50
60
Passing
%Passing 60
30
40% P
%Passing = 30
10
20%Passing = 10
0
0.0010.010.1110Particle size (mm) D
D30100
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Particle size (mm) D60 D10
G i Si Di t ib tiGrain Size Distribution
• 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
G i Si Di t ib tiGrain Size Distribution
• 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
90
100
Well graded Uniformly graded
oo y g aded
60
70
80
9
g
Gap graded
30
40
50
60
% Passin
0
10
20
30
Dr. Asmaa Moddather – PBW N302 – Fall 2012
0
0.0010.010.1110Particle size
(mm)
100
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
100
80
90
60
70
ing
%Passing = 60
40
50
% Passi
%Passing 30
20
30%Passing = 30
%Passing 10
0
10%Passing = 10
D
Dr. Asmaa Moddather – PBW N302 – Fall 2012
0.0010.010.1110Particle size (mm) D60
D30
D10
100
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.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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”.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
y y g
Att b (C i t ) Li itAtterberg (Consistency) Limits
Adding waterVolume
Liquid
Plastic
Liquidlimit
limit
Shrinkage
AA W
Wg
limitDry soil
S
A
S
W
S SS
W
S SWater content
S SS
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
g y
Li id Li it T tLiquid Limit Test
Liquid limit device
Dr. Asmaa Moddather – PBW N302 – Fall 2012Grooving tool
Li id Li it T tLiquid Limit Test
Dr. Asmaa Moddather – PBW N302 – Fall 2012
Li id Li it T tLiquid Limit Test
•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
Water content
wL wL
No. of blows
25
Log No. of blows
25
Dr. Asmaa Moddather – PBW N302 – Fall 2012
g
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.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
wax.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
A W
vv = vT – vs
v vw wwww = vv γw vT
vvvT
w ww
S SSh.L. = ww/wswsvs wsvs
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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 <( )
Dr. Asmaa Moddather – PBW N302 – Fall 2012
(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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
5
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
p
R l ti D it f C G i d S ilRelative Density of Coarse Grained Soil
100xee(%)D actmaxr
−=
ee( )
minmaxr −
Type of SoilDr (%)
Very loose0 – 15
Loose15 – 35
Medium dense35 ‐ 65
Dense65 – 85
Very dense85 ‐ 100
Dr. Asmaa Moddather – PBW N302 – Fall 2012
S il Cl ifi tiSoil Classification
• There are many different soil classification systems in
use:
o MIT classification systemo MIT classification system.
o Unified Soil Classification System (USCS).
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
y
y
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
100
Gravel Sand Silt Clay
80
90
60
70
ing
40
50
% Passi
20
30
0
10
Dr. Asmaa Moddather – PBW N302 – Fall 2012
0.0010.010.1110Particle size (mm)
100
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
% P
Dr. Asmaa Moddather – PBW N302 – Fall 2012
010
0.0010.010.1110Particle size (mm)
100
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%
Dr. Asmaa Moddather – PBW N302 – Fall 2012
y
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:
L.L.
Dr. Asmaa Moddather – PBW N302 – Fall 2012
P.L.
P.I.
ifi d il l ifi iUnified Soil Classification System (USCS)
• 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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
L.L. > 50% (high plasticity) H
ifi d il l ifi iUnified Soil Classification System (USCS)
• % 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
Coa
rse‐grai
nd
• % Gravel = 100 ‐ % Passing sieve No. 4Sieve No. 200
il
San
• % S d % P i i N % P i i N e‐graine
d so
Silt & Clay
Dr. Asmaa Moddather – PBW N302 – Fall 2012
• % Sand = % Passing sieve No. 4 ‐ % Passing sieve No. 200
FineS
USCS S T blUSCS Summary Table
Use plasticity chart to determine M or C
Use plasticity chart to determine M or C
Use Plasticity Chart oo
bbbbbbbbbbbbboo
Dr. Asmaa Moddather – PBW N302 – Fall 2012
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
Dr. Asmaa Moddather – PBW N302 – Fall 2012
ML, MH
Pl ti it Ch t (A Li )Plasticity Chart (A‐Line)
60
40
50
(%) CH
30
40
ty In
dex
CL Ip = 0.73(wL-20)
20
Plas
ticit
MH
0
10MLCL-ML ML
ML0
0 10 20 30 40 50 60 70 80 90 100
Liquid Limit (%)
Dr. Asmaa Moddather – PBW N302 – Fall 2012
( )
ifi d il l ifi iUnified Soil Classification System (USCS)% Passing sieve No. 200
< 50% > 50%< 50% 5
Fine‐grained soilCoarse‐grained soil
% 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
SW SP
Care for fines
Inspect L.L., P.I., A‐line
SC SM
SW‐SC
SP‐SM
Dual symbol
Dr. Asmaa Moddather – PBW N302 – Fall 2012
SW, SP
GW, GP
SC, SM
GC, GMGW‐GM
GP‐GC
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
% Passing sieve No. 4
G lS d(A‐line)
LL & PI
GravelSand
% Passing sieve No. 200
< 5% 5% ‐ 12% > 12%
Care for gradation Care for finesDual symbol
CH, CL
ML MH
Care for gradation
SW, SP
GW GP
Care for fines
SC, SM
GC GM
SW‐SC
SP‐SM
Dual symbol
Dr. Asmaa Moddather – PBW N302 – Fall 2012
ML, MHGW, GP GC, GMGW‐GM
GP‐GC