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ContentsRef: - Supplementary Notes for TA C222
Soil Classification Grain Size Distribution Liquid Limit and Plastic Limit
Field Identification of Soils
Rock Cycle – Soil Formation
Soils The final products due to weathering are soils
IntroductionObject:To keep various types of soils into groups according to their propertiesSoil consisting of similar characteristics Can be placed in the SAME Group
Need:To find the suitability of the soil for construction of dams, highways and foundations
Types of Soil Classification
1. Partcle Size Classification
2. Unified Soil Classification System (USCS)
3. Textural Classification
4. Public Roads Administration Classification (AASHTO, 1978)
Particle Size Classification
Soils are according to Grain Size
Various grain size classifications are in use
Grain size distribution of soil is required
Percentage of soil in each size group is determined
Example: Soil 10% Gravel + 52% Sand + 38% Silt & Clay
Origin of USCS:
This system was first developed by Professor Casagrande (1948) for the purpose of airfield construction during World War II. Afterwards, it was modified by Professor Casagrande to enable the system to be applicable to dams, foundations, and other construction
Four major divisions:(1)Coarse-grained(2)Fine-grained(3)Organic soils(4)Peat
Unified Soil Classification System (USCS)
BouldersSilt Clay
2.0 mm 0.425 mm
CobblesGravel Sand
Coarse Fine Coarse FineMedium
300 mm 80 mm
20 mm
4.75 mm 0.075 mm
0.002 mm
Coarse Grained SoilsFine
Grained Soils
Unified Soil Classification System
Coarse-grained soils:
Gravel Sand
Fine-grained soils:
Silt Clay
0.075 mm
•Grain size distribution
•Cu
•Cc
•PL, LL
•Plasticity chart
50 %
4.75 mm
Sieve analysis Atterberg limits
Unified Soil Classification System
Particle size
Question For the purpose of engineering descriptions, soils are divided into classes of similar grain size. The NOUNS used to describe a size class refer to a specific range of sizes.
What is the range of sizes of SAND?
0.075 mm to 0.425 mm 0.425 mm to 4.75 mm 0.075 mm to 4.75 mm 2.0 mm to 4.75 mm
What is the range of sizes of FINE SAND particles?
0.075 mm to 0.425 mm 0.425 mm to 4.75 mm 0.075 mm to 4.75 mm 2.0 mm to 4.75 mm
0.075 – 4.75 mm
0.075 – 0.425 mm
USCS
Particle size
Question For the purpose of engineering descriptions, soils are divided into classes of similar grain size. The NOUNS used to describe a size class refer to a specific range of sizes.
What is the range of sizes of MEDIUM SAND?
0.075 mm to 0.425 mm 0.425 mm to 2.0 mm 0.075 mm to 4.75 mm 2.0 mm to 4.75 mm
What is the range of sizes of SILT particles?
0.002 mm to 0.425 mm 0.002 mm to 4.75 mm 0.002 mm to 0.075 mm <0.002 mm
0.425 – 2.0 mm
0.002 – 0.075 mm
USCS
Particle size
Question For the purpose of engineering descriptions, soils are divided into classes of similar grain size. The NOUNS used to describe a size class refer to a specific range of sizes.
What is the range of sizes of Gravel?
2 mm to 4.75 mm 4.75 mm to 20 mm 4.75 mm to 80 mm 20 mm to 80 mm
What is the range of sizes of CLAY particles?
0.002 mm to 0.425 mm 0.002 mm to 4.75 mm 0.002 mm to 0.075 mm <0.002 mm
4.75 – 80 mm
< 0.002 mm
USCS
Grain Size Distribution
Coarse-grained soils:
Gravel Sand
Fine-grained soils:
Silt Clay
0.075 mm (USCS)
•Experiment
Sieve analysis Hydrometer analysis
Classification of Coarse Grained 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
Schematic diagram of hydrometer test
At the beginning Towards the end of test
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
CD
Du 60
10
CD
D Dc 302
60 10( )
x% of the soil has particles smaller than Dx
D60
Grain Size Distribution Curves
where CU is Coefficient of Uniformity and Cc is Coefficient of Curvature
Grain Size Distribution Curves
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
A Well graded Soil
B Uniform Soil (or Poorly Graded Soil)
C Gap Graded Soil (or Poorly graded soil)
D Well graded with some fines
E Well graded with an excess of fines
A
C
B
D
E
To determine Well Graded (W) or Poorly Graded (P), calculate Cu and Cc.
If prefix is G (Gravel) then suffix is W if Cu > 4 and Cc is between 1 and 3
otherwise use P
If prefix is S (Sand) then suffix is W if Cu > 6 and Cc is between 1 and 3
otherwise use P
CD
Du 60
10
CD
D Dc 302
60 10( )
Unified Soil Classification System (USCS)
where CU is Coefficient of Uniformity and Cc is Coefficient of Curvature
Describe the following Soil
2)9)(02.0(
)6.0(
)D)(D(
)D(C
curvatureoftCoefficien
45002.0
9
D
DC
uniformityoftCoefficien
2
6010
230
c
10
60u
mm9D
mm6.0D
)sizeeffective(mm02.0D
60
30
10
)(
631
)(
431
sandsfor
CandC
gravelsfor
CandC
soilgradedWell
uc
uc
Well Graded Soil
Criteria
USCS
QuestionWhat is the Cu for a soil with only one grain size?
D
Fin
er
1D
DC
uniformityoftCoefficien
10
60u
Grain size distribution
The grading curve for a soil gives the size characteristics:
d10 = 0.16 mm and d60 = 0.47 mm
What is the Uniformity coefficient (Cu) and gradation
of the soil?
0.34, well graded 2.94, well graded 2.94, uniformly graded 0.34, uniformly graded
2.94, Uniformly (or Poorly) Graded Sand
Question
-- Atterberg Limits (or Consistency Limits)
Shrinkage Limit, SL
Liquid Limit, LL
Liquid State
Plastic Limit, PL
Plastic State
Semisolid State
Solid StateDry Soil
Soil-water mixture
Incr
easi
ng w
ater
con
tent
Classification of Fine Grained SoilsUSCS
Volume Change with water content
Atterberg Limits (or Consistency Limits) - Cont.
Liquid and plastic limits
Question The figure shows how volume and water content are related in fine soils. Identify the consistency of zones A, B and C?
A. Semi-solid B. Plastic C. Liquid
Where
ws: shrinkage limit
wP: Plastic Limit
wL: Liquid Limit
Plastic Limit, Liquid Limit
Liquid and plastic limits
The lower and upper limits of the PLASTIC range are used to
classify the fine soils.
Plasticity Index = Liquid Limit – Plastic Limit
The difference between the liquid limit (wL) and plastic limit (wP) is called as
PLASTICITY INDEX (P.I.)
Plasticity Index
Liquid Limit - LL (or wL)
•Cone Penetrometer Method
This method is developed by the Transport and Road Research Laboratory, UK.
•Casagrande Method
Professor Casagrande standardized the test and developed the liquid limit device.
LL - Casagrande Method
N=25 blows
Closing distance = 10 mm
•Device
The water content, in percentage, required to close a distance of 10 mm along the bottom of the groove after 25 blows is defined as the liquid limit
LL - Casagrande Method (Cont.)
12
21
/log,
NN
wwIindexFlow F
N
w
LL - Cone Penetrometer Method31o Cone of Stainless steel
Total sliding weight of 148 g
Cylindrical mould of 5 cm diameter and 5 cm height.
Water content w%Pen
etra
tion
of c
one
(mm
)
25 mm
LL
)15)(25(01.0 xxL wxww
Where x is the depth of penetration of cone in mmwx is water content corresponding to penetration x
For x = 20 to 30
Plastic Limit – PL (or wP)
The plastic limit is defined as the water content at which a soil thread with 3 mm diameter just crumbles.
Soil symbols: G: Gravel S: Sand M: Silt C: Clay O: Organic Pt: Peat
Liquid limit symbols: H: High LL (LL > 50) L: Low LL (LL < 50)
Gradation symbols: W: Well-graded P: Poorly-graded
Ex: SW: Well-graded Sand
SC: Clayey Sand
SM: Silty Sand
)(
631
)(
431
sandsfor
CandC
gravelsfor
CandC
soilgradedWell
uc
uc
SYMBOLS Used for USCS Soil Classification
Above A-line use suffix C – ClayBelow A-line use suffix M – Silt
LL < 50% use Prefix LLL > 50% use Prefix H
Fine grained soils Silt (M) & Clay (C)To determine M or C use plasticity chart
0 10 20 30 40 50 60 70 80 90 10 0Liquid li m it
0
10
20
30
40
50
60
Plas
tici
tyin
dex
O
or
H
H
HO
or
C
CC
MM
M
LL
L
L
L
"" l n
Ai e
o paring soils at equal liq uid li mit
Toug h ness and dry stre ngth in crease
with increasin g plasticity in dex
Plasticity Chart
Classification of Fine Grained Soils
Use “O” below A – Line, if
Soil is Organic
A – Line
PI = 0.73(wL – 20)
USCS
Fine-grained soils with limits within the shaded zone (i.e., PI between 4 and 7 and LL between 12 and 25).It is hard to distinguish between the silt and claylike
materials.Use: CL-ML: Silty clay & SC-SM: Silty,
clayed sand.
Classification of Fine Grained Soils - Cont.
Borderline Cases (Dual Symbols)
Coarse-grained soils with 5% - 12% fines.The first symbol indicates whether the coarse fraction is
well or poorly graded. The second symbol describe the contained fines (M/C).
Example: SP-SM: Poorly graded Sand with Silt.
USCS
Coarse-grained material
Grain size distribution
Fine-grained material
LL, PI
Highly
Unified Soil Classification System (USCS)
Passing No.200 sieve 30 %
Passing No.4 sieve 70 %
LL= 33
PI= 12
PI= 0.73(LL-20), A-line
PI=0.73(33-20)=9.49
SC (15% gravel)
Clayey sand with gravel
Passing No.200 (0.075 mm) sieve = 30 %
Passing No.4 (4.75 mm) sieve = 70 %
LL= 33%
PI= 12%
Highly
ExampleUSCS
Textural Classification1. IS 1498 – 1970 System
2. U S Bureau of Soils and Chemistry System
Grain size distribution of soil is required
Percentage of soil in each size group is determined
Ex:- Soil 10% Gravel + 52% Sand + 38% Silt & Clay
IS 1498 – 1970 System
U S Bureau of Soils and Chemistry System
First find the percentages of SAND, SILT and Clay. Based on the RELATIVE percentages of sand, silt and clay a
POINT is located on the TRIANGULAR CHART which indicates SOIL TYPE.
10 09080706050403020100
10 0
90
80
70
60
50
40
30
20
10
010 0
90
80
70
60
50
40
30
20
10
0
Silt Sizes ( %)
San d
Siz e
s(%
) Cla y
S izes( %
)
SandSilty San d Sandy Sil t
Clay -S an d Clay -S ilt
Sandy Clay Silty Clay
Clay
Public Roads Administration Classification System (AASHTO 1978 System)
Based on both particle size composition and plasticity characteristics
GROUP INDEX of the soil is determined in order to rate the soil as a SUBGRADE MATERIAL for PAVEMENT construction
HIGHER the value of GROUP INDEX, POORER is the QUALITY of the SOIL.
Field Identification of SoilsDistinguish Gravel from Sand
Sand from Silt
Silt from Clay
Grain Size
Dispersion Test
Dispersion Test Shaking (Dilatancy) Test Strength Test Rolling (Toughness) Test
Organic Content and Color
Organic soils usually have a distinctive odour of decomposed organic
matter, which can be detected by heating.
Acid Test – use dilute HCL to check the presence of Calcium Carbonate
Shine Test – Highly Plastic soil is more Shine than Low Plastic soil