CIVE 353
Soil Classification
Clay Soils
1
STATE
Increasing water
content
STRESS-STRAIN BEHAVIOUR AT
VARIOUS STATES
Stress
Liquid
Liquid Limit (LL)
Strain
Stress
Plastic
Non-linear inelastic
Plastic Limit (PL)
Semi- Solid
Elastic - Plastic
Strain
Stress
Shrinkage Limit (SL)
Linear elastic – brittle failure
Strain
Solid
2
Liquid Limit (LL)
3
Atterberg Device
Liquid Limit (LL)
Moisture content that closes gaps @ 25 blows
4
Liquid Limit (LL)
Moisture content @ penetration = 20mm
Plastic Limit (PL)
Roll clay until
it breaks at
1/8 inch thick
(3.2mm)
5
Plastic Index (PI)
STATE
Increasing
moisture
content
Liquid
Liquid Limit (LL)
PI = LL-PL
Plastic
Plastic Limit (PL)
Semi- Solid
LL = PL
PI = 0 Non plastic (silt)
LL > PL
PI > 0 Plastic clays
Shrinkage Limit (SL)
Solid
Burmister (1949) Classification
PI
Description
0
Nonplastic
1-5
Slightly plastic
5-10
Low plasticity
10-20
Medium plasticity
20-40
High plasticity
>40
Very high plasticity
6
Activity (A)
A=
PI
( percent clay − size fraction by weight )
A=
PI
(percent clay - size fraction by weight)
7
Plasticity Index and Clay Content
Atterberg Limits and Clay Minerals
8
Liquidity Index (LI)
w - PL w - PL
LI =
=
LL - PL
PI
‡
Compares field water content with
LL and PL.
LI=0
LI=1
w1
w2
PL
PI
LI>1
w3
LL
Bulky Soils
9
Sieve Analysis
10
Fine sand, silt and clay
Soil fraction passing
No. 40 sieve (0.425mm)
D(mm) = K
L(cm)
t (min)
K = f(temp and Gs)
11
12
Poorly graded
Well graded
Gap graded
Particle Size Definitions
13
Particle Size Distribution Curves
Cu =
D60
= Coefficent of Uniformity
D10
D 2 30
Cc =
= Coefficent of Gradiation
D60 x D10
Grain Size Distribution
14
Unified Soil Classification
System
(USCS)
UNIFIED Soil Classification System (USCS)
Particle diameter (mm)
Boulder
Cobble
Gravel
Sand
Silt
Clay
Colloid
> 300
76.2 - 300
4.75 – 76.2
0.075 – 4.75
.005 – 0.075
0.002 - .005
< 0.002
Bulky
Particles
Plate/Needle
Particles
15
Soil Classification Systems
16
17
18