classification of soil details aas per is ,us,classification geotechnical engineering

Problem: An undisturbed saturated specimen of clay
has a volume of 18.9 cm3
and a mass of 30.2 g. On
oven drying, the mass reduces to 18 g. The volume
of dry specimen as determined by displacement of
mercury is 9.9 cm3
. Determine shrinkage limit,
specific gravity, shrinkage ratio and volumetric
shrinkage.
Solution:
M1= 30.2g, Md = 18g, ρw = 1 g/cc
V1 = 18.9 cm3 V2 = 9.9 cm3

i) ws = [(M1 – Md)/Md] – [(V1 – V2)x ρw /Md] x 100
= [(30.2-18)/18] – [(18.9 – 9.9) x 1/18] x 100
= 17.8%
ii) G = Md/(V1-(M1 – Md))
= 18/(18.9 –(30.2- 18))
= 2.69
Alternatively G = 1 /[(ρw / ρd) – (ws /100)]
ρd = 18/9.9 = 1.818 g/cc
ρw = 1 g/cc
From i), ws = 17.8%
G = 2.69

iii) SR = ϒd/ϒw = ρd/ ρw = Gm = 1.818/1
= 1.82
IV) Volumetric Shrinkage (VS)
VS = [(V1 – Vd) x 100]/Vd
= [(18.9 – 9.9) X 100] /9.9 = 91%
Alternatively,
VS = (w1 –ws) SR
= (67.8 – 17.8) X 1.82 = 91%

Pr 2: The mass specific gravity of a fully saturated specimen of
clay having a water content of 36% is 1.86. On oven drying, the
mass specific gravity drops to 1.72. Calculate the specific
gravity and its shrinkage limit.
Solution:
e = wsat . G = 0.36 G Gm = ϒsat / ϒw
Gm =[[(G+e) ϒw]/(1+e)] X 1/ ϒw
1.86 = (G+0.36G)/1+0.36G) = 1.36G/(1+0.36G)
G= 2.69
From which,
ws = (ϒw / ϒd) – 1/G
where ϒd / ϒw = 1.72 = mass specific gravity of dry soil
ws = [(1/1.72) – (1/2.69)] = 0.21 = 21%
Alternatively,

Alternatively,
edry = {[(G ϒw / ϒd)] -1 } = {[G ρw/ ρd] -1} = [[2.69 x 1/1.72] -1]
= 0.565
ws = e/G = 0.565/2.69
= 0.21 =21%

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

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.

Purpose
Arrange various types of soils into
groups according to their engineering or
various other characteristics.
Soil possessing similar characteristics
can be placed in the same group.

Soil Classification
Systems
1.Particle Size Classification
2. Textural Classification
3. Highway Research Board (HRB)
Classification
4. Unified Soil Classification System (USCS)
5. Indian Standard Classification System
(ISCS)

Soils arranged according to grain sizes.
Terms such as gravel, sand, silt and clay are
used to indicate grain sizes.
These terms are used only as designation of
particle sizes.
They do not signify naturally occurring
soil types.
Naturally occurring soil are mixture of
particles of different sizes.
Introduction

IS Classification of Grain
Size

Soil classification of composite soils
exclusively based on Particle Size
Distribution.
Most popular is the Triangular Classification of
U.S. Public Roads Administration.
Classification based on % of sand, silt and clay
size.
More suitable for describing coarse grained
soil.
Clay soil properties are less dependent on
Introduction

Example
30% sand
30% silt
40% clay
Soil
Type
Clay

Highway Research Board (HRB)
Classification

Based on both particle-size composition as
well as plasticity characteristics.
Mostly used for pavement construction.
7 primary groups (A-1, A-2,…., A-7).
A-1 subdivided into 2 subgroups.
A-2 subdivided into 4 subgroups.
Introduction to HRB Classification

Used to describe performance of soil when used
for pavement construction.
Not used to place a soil in a particular group.
It means rating the value of soil as a subgrade
material within its own group.
Higher the value of GI, poorer is the quality of
material.
Group Index (GI)

Group Index of a soil depends on:
1. Amount of material passing 75 micron IS sieve.
2. Liquid Limit.
3. Plastic Limit.
Group Index
determination

 Proceed from left to right on the chart.
 Correct group will be found by process of elimination.
 The first group from left into which the test data will fit will be
the correct classification.
 Group Index should be rounded off to nearest integer and
placed in parenthesis, such as, A-2-2 (6).

Unified Soil Classification
System USCS

Origin of USCS
 First developed by Professor A.
Casagrande (1948) for the purpose of
airfield construction during World War II.
 Afterwards, it was modified to enable the
system to be applicable to dams,
foundations, and other construction .

Four Major
Divisions
Course
Grained
Fine
Graine
d
Organi
c
Soil
Peat

Classification Groups
•The soil is classified into 15 groups.
•Each group is designated a symbol
consisting of two capital letters.
•The first letter is based on main soil type.
•The second letter is based on gradation
and plasticity .

Classification Group Symbols
Main Soil
Type
Prefix Subgroup Suffix
Classification
Group symbols
Gravel G
Well-graded
Poorly-
graded Silty
Clayey
W
P
M
C
GW
GP
GM
GC
Sand S
Well-graded
Poorly-
graded Silty
Clayey
W
P
M
C
S
W
SP
SM
SC
Silt M
LL < 50%
LL > 50%
L
H
ML
M
H
Clay C
LL < 50%
LL > 50%
L
H
CL
CH
Organic O
LL < 50%
LL > 50%
L
H
OL
OH

Unified Soil Classification System (Contd.)

Plasticity Chart
Below A-line, use M (Silt)
or O (Organic)
Above A-line, use C - Clay
High Plasticity use H - wL >50
Low Plasticity use L - wL <50
Silt (M)
Clay (C)
Organic
(O)

Plasticity Chart
“The soil’s liquid limit (wL) after oven drying is less than 75 % of its
liquid
limit before oven drying.” If the above statement is true, then it is
Organic Soil (OL or OH). Otherwise, it is Inorganic Soil (ML or MH)

Plasticity Chart
When IP and wL are in the hatched portion of the plasticity chart, the
soil is
given dual symbol (CL-ML).
Soil possessing properties of more than one group are termed as
boundary
soil and designated by dual group

USCS at a glance
+
(Santamarina et al.,
2001)

Group Symbols and Group Names
Group Symbol Typical Name
GW Well-graded gravels.
GP Poorly-graded gravels.
GM Silty gravels.
GC Clayey gravels
SW Well-graded sands.
SP Poorly-graded sands.
SM Silty sands.
SC Clayey sands.

Group Symbol Typical Name
CL Inorganic clays of low plasticity.
ML Inorganic silts with slight plasticity.
OL Organic soil of low plasticity.
CH Inorganic clays of high plasticity.
MH Inorganic silts with high plasticity.
OH Organic soil of high plasticity.
Pt Peat.
Group Symbols and Group Names

Indian Standard Classification System (ISCS)
I S : 1498-1970

Introduction
Based on USCS
system
Modificationsare:
Fine grained soils subdivided into 3 groups
(low, intermediate and high plasticity) as
against two groups(low and high) in USCS.
wL <35 = L ,
 35 <WL < 50 =I ,
 wL > 5 0 = H
Thus, soil classified into 18 groups as

Classification Group Symbols
Main
Soil
Type
Prefix Subgroup Suffix
Classification
Group
symbols
Gravel G
Well-graded
Poorly-
graded Silty
Clayey
W
P
M
C
GW
GP
GM
GC
Sand S
Well-graded
Poorly-
graded Silty
Clayey
W
P
M
C
S
W
SP
SM
SC
Silt M
LL < 35%
35<LL<>5
0 LL >
50%
L
I
H
ML
MI
M
H
Clay C
LL < 35%
35<LL<>5
0 LL >
50%
L
I
H
CL
CI
CH
LL < 35% L OL

Plasticity Chart
High Plasticity use H - wL >50
Intermediate Plasticity use I – 35< wL >50
Low Plasticity use L - wL <35
Below A-line, use M (Silt)
or O (Organic)
Above A-line, use C - Clay

Grading Curves
0.0001 0.001 0.01 0.1 1 10 100
0
20
40
60
80
100
Particle size (mm)
%
F
ine
r
W - Well graded
P – Poorly graded
Gap graded

Boundary Classification
Coarse grained soils:
GW –GP, GM-GC, GW-GM, GW_GC, SW-SP,
SM-SC, SW-SM,
Fine grained soils:
ML-MI,CL-CI,MI-MH, CH-OH
Coarse and fine grained soils: SM-SL, SC-CL
In coarse grained soils, if fines between 5 to
10% and PI between 4 to 7soils can be
represented as GM &GC or SC
such cases Non Plastic classification is
favoured

Problem:
Sketch the plasticity chart used for classifying fine
grained soil in the IS soil classification system.
Give the group symbols for the following soils
i) Liquid limit = 40% Plastic limit = 22%
ii) Liquid limit = 20% Plastic limit = 14%
iii) Passing 4.75 mm sieve = 70%, Passing 75 µ sieve = 8%
Cu = 7, Cc = 3, PI = 3

Solution
i) Liquid limit = 40% Plastic limit = 22%
PI = WL – Wp = 40 – 22 = 18%
WL = 40% and PI = 18%, from the Plasticity
chart Group symbol = CI

ii) Liquid limit = 20% Plastic limit = 14%
PI = WL – Wp = 20 – 14 = 6%
WL = 20% and PI = 6%, from the Plasticity
chart Group symbol = CL-ML

iii) Since greater than 70% is passing through
4.75 mm sieve, the soil is Sandy (S)
Cu = 7 i.e >6 and Cc = 3, hence soil is SW
But % passing through 75 µ sieve is 8% (b/w 5 to
12%) It is a boarder line case.
Also, PI = 3, (<4) it satisfy the requirement of SM.
Hence the soil is designated as SW-SM

Hydrometer Analysis
https://www.youtube.com/watch?v=GfDW3Fw9cL0

Thank You
Reference from internet and text books

classification of soil details aas per is ,us,classification geotechnical engineering

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