38623 soil classification
DESCRIPTION
bookTRANSCRIPT
Soils and their Classification
Soils - What are they?
Particulate materials
- Sedimentary origins (usually)- Residual
Wide range of particle sizes
- larger particles: quartz, feldspar- very small particles: clay minerals
Voids between particles
Aragonite-rich soil x 2000
Need for Simple Classification
Usually soil on site has to be used.– Soils differ from other engineering materials in that one
has little control over their properties
Extent and properties of the soil have to be determined
Cheap and simple tests are required to give an indication of engineering properties, e.g. stiffness, strength, for preliminary design
The classification must use core samples obtained from the ground. This information is often supplemented by in-situ tests such as cone penetration tests.
Classification based on Particle Size Particle size is used because it is related to mineralogy
– e.g. very small particles usually contain clay minerals
Broad Classification
– Coarse grained soils» sands, gravels - visible to naked eye
Classification based on Particle Size Particle size is used because it is related to mineralogy
– e.g. very small particles usually contain clay minerals
Broad Classification
– Coarse grained soils» sands, gravels - visible to naked eye
– Fine grained soils» silts, clays, organic soils
Procedure for grain size determination Sieving - used for particles > 75 m
Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity proportional to diameter
Procedure for grain size determination Sieving - used for particles > 75 m
Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity proportional to diameter
Figure 1 Schematic diagram of hydrometer test
Procedure for grain size determination Sieving - used for particles > 75 m
Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity proportional to diameter
Figure 1 Schematic diagram of hydrometer test
Grading curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
W Well graded
Grading curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
W Well graded
U Uniform
Grading curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
W Well graded
U Uniform
P Poorly graded
Grading curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
W Well graded
U Uniform
P Poorly graded
C Well graded with some clay
Grading curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
W Well graded
U Uniform
P Poorly graded
C Well graded with some clay
F Well graded with an excess of fines
Simple Classification In general soils contain a wide range of particle sizes
Some means of describing the characteristics of soils with different proportions of sand/silt/clay is required.
Simple Classification In general soils contain a wide range of particle sizes
Some means of describing the characteristics of soils with different proportions of sand/silt/clay is required.
1009080706050403020100
100
90
80
70
60
50
40
30
20
10
0100
90
80
70
60
50
40
30
20
10
0
SiltSizes(%)
SandSiltySand SandySilt
Clay-Sand Clay-Silt
SandyClay SiltyClay
Clay
LOWERMISSISSIPPIVALLEYDIVISION,U.S.ENGINEERDEPT.
Simple Classification In general soils contain a wide range of particle sizes
Some means of describing the characteristics of soils with different proportions of sand/silt/clay is required.
Note the importance of clay - Finest 20% control behaviour1009080706050403020100
100
90
80
70
60
50
40
30
20
10
0100
90
80
70
60
50
40
30
20
10
0
SiltSizes(%)
SandSiltySand SandySilt
Clay-Sand Clay-Silt
SandyClay SiltyClay
Clay
LOWERMISSISSIPPIVALLEYDIVISION,U.S.ENGINEERDEPT.
Example: equal amounts sand/silt/clay
Example: equal amounts sand/silt/clay
Example: equal amounts sand/silt/clay
Atterberg Limits Particle size is not that useful for fine grained soils
Atterberg Limits Particle size is not that useful for fine grained soils
Figure 4 Moisture content versus volume relation during drying
010203040
0 20 40 60Moisture Content (%)
Volu
me
LLSL PL
Atterberg Limits Particle size is not that useful for fine grained soils
Figure 4 Moisture content versus volume relation during drying
SL - Shrinkage Limit PL - Plastic Limit LL - Liquid limit
010203040
0 20 40 60Moisture Content (%)
Volu
me
LLSL PL
Atterberg Limits
SL - Shrinkage LimitPL - Plastic LimitLL - Liquid limit
Atterberg Limits
SL - Shrinkage LimitPL - Plastic LimitLL - Liquid limit
Plasticity Index = LL - PL = PI or Ip
Atterberg Limits
SL - Shrinkage LimitPL - Plastic LimitLL - Liquid limit
Plasticity Index = LL - PL = PI or Ip
Liquidity Index = (m - PL)/Ip = LI
Classification Systems Used to determine the suitability of different soils
Used to develop correlations with useful soil properties
Special Purpose (Local) Systems– e.g. PRA system of AAHSO
» 1. Well graded sand or gravel: may include fines» 2. Sands and Gravels with excess fines» 3. Fine sands» 4. Low compressibility silts» 5. High compressibility silts» 6. Low to medium compressibility clays» 7. High compressibility clays» 8. Peat and organic soils
Unified Soil Classification Each soil is given a 2 letter classification (e.g. SW). The
following procedure is used.
Unified Soil Classification Each soil is given a 2 letter classification (e.g. SW). The
following procedure is used.
– Coarse grained (>50% larger than 75 m)
Unified Soil Classification Each soil is given a 2 letter classification (e.g. SW). The
following procedure is used.
– Coarse grained (>50% larger than 75 m)
» Prefix S if > 50% of coarse is Sand» Prefix G if > 50% of coarse is Gravel
Unified Soil Classification Each soil is given a 2 letter classification (e.g. SW). The
following procedure is used.
– Coarse grained (>50% larger than 75 m)
» Prefix S if > 50% of coarse is Sand» Prefix G if > 50% of coarse is Gravel
» Suffix depends on %fines
Unified Soil Classification Each soil is given a 2 letter classification (e.g. SW). The
following procedure is used.
– Coarse grained (>50% larger than 75 m)
» Prefix S if > 50% of coarse is Sand» Prefix G if > 50% of coarse is Gravel
» Suffix depends on %fines
» if %fines < 5% suffix is either W or P» if %fines > 12% suffix is either M or C» if 5% < %fines < 12% Dual symbols are used
Unified Soil ClassificationTo determine if W or P, calculate Cu and Cc
CDDu 60
10
CD
D Dc 302
60 10( )
x% of the soil has particles smaller than Dx
Unified Soil ClassificationTo determine W or P, calculate Cu and Cc
CDDu 60
10
CD
D Dc 302
60 10( )
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
x% of the soil has particles smaller than Dx
Unified Soil ClassificationTo determine W or P, calculate Cu and Cc
CDDu 60
10
CD
D Dc 302
60 10( )
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
x% of the soil has particles smaller than Dx
Unified Soil ClassificationTo determine W or P, calculate Cu and Cc
CDDu 60
10
CD
D Dc 302
60 10( )
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
D90 = 3 mm
x% of the soil has particles smaller than Dx
Unified Soil Classification
To determine W or P, calculate Cu and Cc
If prefix is G then suffix is W if Cu > 4 and Cc is between 1 and 3
otherwise use P
If prefix is S then suffix is W if Cu > 6 and Cc is between 1 and 3
otherwise use P
CDDu 60
10
CD
D Dc 302
60 10( )
Unified Soil Classification
0 10 20 30 40 50 60 70 80 90 100Liquid limit
0
10
20
30
40
50
60
Plasti
cityi
ndex
CH
OH
or
MH
CLOL
MLor
CL
ML
Comparing soils at equal liquid limitToughness and dry strength increasewith increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
Coarse grained soilsTo determine M or C use plasticity chart
Below A-line use suffix M - Silt
Above A-line use suffix C - Clay
Unified Soil Classification– Fine grained soils (> 50% finer than 75 m)– Both letters determined from plasticity chart
0 10 20 30 40 50 60 70 80 90 100Liquid limit
0
10
20
30
40
50
60
Plas
ticity
index
CH
OH
or
MH
CLOL
MLor
CL
ML
Comparing soils at equal liquid limitToughness and dry strength increasewith increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
Give typical names: indicate ap-proximate percentages of sandand gravel: maximum size:angularity, surface condition,and hardness of the coarsegrains: local or geological nameand other pertinent descriptiveinformation and symbol inparentheses.
For undisturbed soils add infor-mation on stratification, degreeof compactness, cementation,moisture conditions and drain-age characteristics.
Example:
Well graded gravels, gravel-sand mixtures, little or nofinesPoorly graded gravels, gravel-sand mixtures, little or nofinesSilty gravels, poorlygraded gravel-sand-silt mixtures
Clayey gravels, poorly gradedgravel-sand-clay mixtures
Well graded sands, gravellysands, little or no fines
Poorly graded sands, gravellysands, little or no fines
Silty sands, poorly gradedsand-silt mixtures
Clayey sands, poorly gradedsand-clay mixtures
GW
GP
GM
GC
SW
SP
SM
SC
Wide range of grain size and substantialamounts of all intermediate particlesizesPredominantly one size or a range ofsizes with some intermediate sizesmissingNon-plastic fines (for identificationprocedures see ML below)
Plastic fines (for identification pro-cedures see CL below)
Wide range in grain sizes and sub-stantial amounts of all intermediateparticle sizes
Predominantely one size or a range ofsizes with some intermediate sizes missing
Non-plastic fines (for identification pro-cedures, see ML below)
Plastic fines (for identification pro-cedures, see CL below)
ML
CL,CI
OL
MH
CH
OH
Pt
Dry strengthcrushingcharacter-
istics
None toslight
Medium tohigh
Slight tomedium
Slight tomedium
High to veryhigh
Medium tohigh
Readily identified by colour, odourspongy feel and frequently by fibroustexture
Dilatency(reactionto shaking)
Quick toslow
None to veryslow
Slow
Slow tonone
None
None to veryhigh
Toughness(consistencynear plastic
limit)
None
Medium
Slight
Slight tomedium
High
Slight tomedium
Inorganic silts and very fine sands,rock flour, silty or clayeyfine sands with slight plasticityInorganic clays of low to mediumplasticity, gravelly clays, sandyclays, silty clays, lean claysOrganic silts and organic silt-clays of low plasticityinorganic silts, micaceous ordictomaceous fine sandy orsilty soils, elastic siltsInorganic clays of highplasticity, fat clays
Organic clays of medium tohigh plasticity
Peat and other highly organic soils
Give typical name; indicate degreeand character of plasticity,amount and maximum size ofcoarse grains: colour in wet con-dition, odour if any, local orgeological name, and other pert-inent descriptive information, andsymbol in parentheses
For undisturbed soils add infor-mation on structure, stratif-ication, consistency and undis-turbed and remoulded states,moisture and drainage conditions
ExampleClayey silt, brown: slightly plastic:small percentage of fine sand:numerous vertical root holes: firmand dry in places; loess; (ML)
Field identification procedures(Excluding particles larger than 75mm and basing fractions on
estimated weights)
Groupsymbols
1Typical names Information required for
describing soilsLaboratory classification
criteria
C = Greater than 4DD----60
10U
C = Between 1 and 3(D )D x D----------------------30
10c
2
60
Not meeting all gradation requirements for GW
Atterberg limits below"A" line or PI less than 4
Atterberg limits above "A"line with PI greater than 7
Above "A" line withPI between 4 and 7are borderline casesrequiring use of dualsymbols
Not meeting all gradation requirements for SW
C = Greater than 6DD---- 60
10U
C = Between 1 and 3(D )D x D----------------------30
10c
2
60
Atterberg limits below"A" line or PI less than 4
Atterberg limits above "A"line with PI greater than 7
Above "A" line withPI between 4 and 7are borderline casesrequiring use of dualsymbolsD
eter
min
epe
rcen
tage
sof
grav
elan
dsa
ndfr
omgr
ain
size
curv
e
Use
grai
nsi
zecu
rve
inid
entif
ying
the
frac
tions
asgi
ven
unde
rfie
ldid
entif
icat
ion
Dep
endi
ngon
perc
enta
ges
offi
nes
(fra
ctio
nsm
alle
rtha
n.0
75m
msi
eve
size
)coa
rse
grai
ned
soils
are
clas
sifie
das
follo
ws
Les
sth
an5%
Mor
eth
an12
%5%
to12
%
GW
,GP,
SW,S
PG
M,G
C,S
M,S
CB
orde
line
case
requ
irin
gus
eof
dual
sym
bols
The
.075
mm
siev
esi
zeis
abou
tthe
smal
lest
parti
cle
visi
ble
toth
ena
ked
eye
Fine
grainedsoils
Morethan
halfof
materialissm
allerthan
.075
mmsievesize
Coarsegrainedsoils
Morethan
halfof
materialislarger
than
.075
mmsievesize
Silts
andclays
liquidlim
itgreaterthan
50
Silts
andclays
liquidlim
itless
than
50
Sands
Morethan
halfof
coarse
fractio
nissm
allerthan
2.36
mm
Gravels
Morethan
halfof
coarse
fractio
nislarger
than
2.36
mm
Sandswith
fines
(app
reciable
amount
offin
es)
Clean
sands
(littleor
nofin
es)
Gravelswith
fines
(apreciable
amount
offin
es)
Clean
gravels
(littleor
nofin
es)
Identification procedure on fraction smaller than .425mmsieve size
Highly organic soils
Unified soil classification (including identification and description)
Silty sand, gravelly; about 20%hard angular gravel particles12.5mm maximum size; roundedand subangular sand grainscoarse to fine, about 15% non-plastic lines with low drystrength; well compacted andmoist in places; alluvial sand;(SM)
0 10 20 30 40 50 60 70 80 90 100Liquid limit
0
10
20
30
40
50
60
Plas
ticity
inde
x
CH
OH
or
MHOL
MLor
CL
Comparing soils at equal liquid limitToughness and dry strength increasewith increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
CI
CL-MLCL-ML
Example
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
Example
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
• %fines (% finer than 75 m) = 11% - Dual symbols required
Example
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
• %fines (% finer than 75 m) = 11% - Dual symbols required
• D10 = 0.06 mm, D30 = 0.25 mm, D60 = 0.75 mm
Example
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
Particle size fractions: Gravel 17%
Sand 73%
Silt and Clay 10%
Of the coarse fraction about 80% is sand, hence Prefix is S
Cu = 12.5, Cc = 1.38
Suffix1 = W
From Atterberg Tests
LL = 32, PL = 26
Ip = 32 - 26 = 6
Example
0 10 20 30 40 50 60 70 80 90 100Liquid limit
0
10
20
30
40
50
60Pl
astic
ityind
ex
CH
OH
or
MH
CLOL
MLor
CL
ML
Comparing soils at equal liquid limitToughness and dry strength increasewith increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
Of the coarse fraction about 80% is sand, hence Prefix is S
Cu = 12.5, Cc = 1.38
Suffix1 = W
From Atterberg Tests
LL = 32, PL = 26
Ip = 32 - 26 = 6
From Plasticity Chart point lies below A-line
Suffix2 = M
Of the coarse fraction about 80% is sand, hence Prefix is S
Cu = 12.5, Cc = 1.38
Suffix1 = W
From Atterberg Tests
LL = 32, PL = 26
Ip = 32 - 26 = 6
From Plasticity Chart point lies below A-line
Suffix2 = M
Dual Symbols are SW-SM
Of the coarse fraction about 80% is sand, hence Prefix is S
Cu = 12.5, Cc = 1.38
Suffix1 = W
From Atterberg Tests
LL = 32, PL = 26
Ip = 32 - 26 = 6
From Plasticity Chart point lies below A-line
Suffix2 = M
Dual Symbols are SW-SM
To complete the classification the Symbols should be accompanied by a description