SOIL MECHANICS
AND FOUNDATION ENGINEERING-I (CE-210)
•
BOOKS
1.
SOIL MECHANICS by T WILLIAM LAMBE & ROBERT V. WHITMAN, Wiley ASTERN
2.
FOUNDATION ANALYSIS & DESIGN by JOSEPH E. BOWLES, Mc Graw Hills
3.
GEOTECHNICAL ENGINEERING by SHASHI K GULHATI & MANOJ DATTA, TATA Mc
Graw Hill
4.
SOIL MECHANICS AND FOUNDATION ENGINEERING by B C PUNMIA, A K JAIN & A
K JAIN, Laxmi Publications Pvt. Ltd.
SYMBOLS
Clay
C
Silt
M
Sand
S
Gravel
G
Cobbles
Cb
Boulders
B
Organic Soil
O
Peat
Pt
GRADATION
𝐷
𝐶𝑢 = 𝐷60
10
𝐶𝑐 =
2
𝐷30
𝐷10 𝐷60
< 2.0 Uniformly Graded; > 2.0 Well Graded
1 to 3 Well Graded
CLASSIFICATION BASED ON PLASTICITY
•
DONE for particles < 75micron
•
Sand Particles (Mica, Quartz, Feldspar, …), even wet, do not stick to each other,
whereas, clay particles in a moist condition do
•
The amount of water present in some soils has a marked influence on their behaviour
•
Sand Particles are electrically neutral
•
Clay particles are made up of minerals e.g. KAOLINITE, ILLITE and
MONTMORILLONITE; electrically charged
CLASSIFICATION BASED ON PLASTICITY
•
Soil in the LIQUID STATE behaves like a LIQUID .i.e. does not possess shear strength.
•
As its water content is reduced to its LIQUID LIMIT, the soil begins to show some very
small shear strength.
•
LIQUID LIMIT: the water content at which soil exhibits some small amount of shear
strength and it is the water content that represents the boundary between the liquid state
and the plastic state.
•
Soil in Plastic State behaves like plastic material i.e. the soil can be moulded, shaped or
distorted without rupture.
•
PLASTIC LIMIT: the soil just begins to rupture or crumble when we try to mould into a
shape.
•
The water content lower than plastic limit, the soil exist in a semi solid state.
•
In this state when water content is further reduced a limit will come when volume of the
soil does not change that is called as SHRINKAGE LIMIT.
•
These limits are generally referred as Atterberg’s Limits.
CLASSIFICATION BASED ON PLASTICITY
CLASSIFICATION BASED ON PLASTICITY
• LL < 35
Low Plasticity
• 35 < LL < 50
Intermediate Plasticity
• > 50
High Plasticity
A-LINE: PI = 0.73 (LL-20)
CLASSIFICATION BASED ON PLASTICITY
• 𝐴𝑐𝑡𝑖𝑣𝑖𝑡𝑦 =
𝑃𝐼
% 𝑐𝑙𝑎𝑦 𝑠𝑖𝑧𝑒 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑝𝑟𝑒𝑠𝑒𝑛𝑡
•
< 0.75 indicates an inactive clay (Kaoline)
•
> 1.25 indicates an active clay (Montmorillonite)
•
> 0.75 and < 1.25 indicates a normal clay (Illite)
• 𝐿𝑖𝑞𝑢𝑖𝑑𝑖𝑡𝑦 𝐼𝑛𝑑𝑒𝑥(𝐿𝐼) =
𝑤 −𝑃𝐿
𝑃𝐼
•
> 1 indicates that the soil is in the liquid state
•
= 1 indicates that the soil is at the liquid limit
•
= 0 indicates that the soil is at the plastic limit
CLASSIFICATION BASED ON PLASTICITY
• 𝐶𝑜𝑛𝑠𝑖𝑠𝑡𝑒𝑛𝑐𝑦 𝐼𝑛𝑑𝑒𝑥(𝐶𝐼) =
𝐿𝐿 −𝑤
𝑃𝐼
•
< 1 indicates that the soil is in the plastic state
•
= 0 indicates that the soil is at the liquid limit
•
= 1 indicates that the soil is at the plastic limit
CLASSIFYING A SOIL
•
In order to classify the soil it is necessary to know its grain size distribution (for coarse
grained soils: gravel and sands) and its Atterberg’s Limits (for fine grained soils: Silts and
Clays)
HOME WORK
Diameter (mm)
Percentage Finer
A
B
C
2.000
100
100
100
1.400
94
100
82
Data from grain size
analysis for three
soils A, B and C is
tabulated here:
0.600
68
100
53
0.425
54
100
45
0.250
30
100
34
0.212
-
-
31
1. Plot the GSD curves
for each soil
0.180
-
97
30
0.150
16
90
30
2. Classify each soil
0.125
-
76
30
3. Calculate Cu and Cc
for each soil
0.090
-
17
-
0.075
4
7
30
0.050
-
-
30
0.010
-
-
15
0.005
-
-
10
0.002
-
-
5
•
•
PROBLEM