Classification of soil

CLASSIFICATION OF SOILS
CREATED BY :-
ALAY MEHTA 141080106011
SHIVANI PATEL 141080106021
KAVIN RAVAL 141080106026
KUNTAL SONI 141080106028
by
PranameshChakraborty
GEOTECHNICS AND APPLIED GEOLOGY
[G.T.A.G.]

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.
3

CLASSIFICATION OF SOIL
 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
6

IS Classification of Grain Size
7

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 particle
size distribution.
Introduction
9

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

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 (GI) DETERMINATION

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
SW
SP
SM
SC
Silt M
LL < 50%
LL > 50%
L
H
ML
MH
Clay C
LL < 50%
LL > 50%
L
H
CL
CH
Organic O
LL < 50%
LL > 50%
L
H
OL
OH
Peat Pt Pt

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)
IS:1498-1970

Introduction
Based on USCS system
Modifications are:
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 <5o=I, wL >50=H
Thus, soil classified into 18 groups as against
15 in USCS.
19

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
SW
SP
SM
SC
Silt M
LL < 35%
35<LL<>50
LL > 50%
L
I
H
ML
MI
MH
Clay C
LL < 35%
35<LL<>50
LL > 50%
L
I
H
CL
CI
CH
Organic O
LL < 35%
35<LL<>50
LL > 50%
L
I
H
OL
OI
OH
Peat Pt Pt 20

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

Classification of soil

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