2. INDEX PROPERTIES OF SOILS
• Used for the identification and classification of soils and
determining the engineering behavior of soils.
• Engineering behavior such as: Strength, Load bearing capacity,
Swelling & shrinkage, Settlement etc.
Index properties of soil are:-
Moisture content/Water content
Specific Gravity
In-situ density/Field density
Particle size distribution/Grain size analysis
Consistency Limits
Relative density/Density index
3. 1.Moisture Content/Water content:-
Methods for determination of water content:
I. Oven Drying Method
II. Pycnometer Method
III. Sand Bath Method
IV. Rapid moisture Method
Oven Drying Method:-
Commonly adopted and simplest method for determining
water content of soil in laboratory.
This method is basically consists of drying a weighted
moist sample of soil in an oven at a controlled
temperature (105oC-110oC ) for a period of 24 hrs.
After which the dry weight of sample is taken.
Temp:- 105oC-110oC (For inorganic soils)
Temp:- 60oC (For organic soils)
4. Clean the container, dry it and weigh it with the lid (Weight
‘W1‘).
Take the required quantity of the wet soil specimen in the
container and weigh it with the lid (Weight ‘W2‘).
Place the container, with its lid removed, in the oven till its
weight becomes constant (Normally for 24 hrs.).
When the soil has dried, remove the container from the
oven, using tongs.
Find the weight ‘W3‘ of the container with the lid and the
dry soil sample.
5. The water content is then calculated by:
Weight of water= Ww =W2 – W3
Weight of solids= Ws = W3 – W1
6. Pycnometer Method:-
The pycnometer method is a rapid method of water content
determination for soils whose specific gravity is accurately
known.
Pycnometer consists of a 900 ml
capacity glass bottle provided with
a conical cap.
A conical cap provided with a 6 mm
diameter hole at the top can be
screwed on the glass bottle.
A rubber washer is placed inside the
conical cap to prevent the leakage of
water through the walls of the
pycnometer and the conical cap.
7. The weight of a clean and dry pycnometer with the cap is taken
and recorded (W1).
About 200-400 g of a wet soil sample is placed in the pycnometer
and the weight of the pycnometer with cap and wet soil is taken
(W2).
Water is added to the pycnometer in increments and the contents
are mixed using a glass rod. Care should be taken to remove the
entrapped air completely by mixing the contents thoroughly.
The pycnometer is then completely filled with water up to the
hole in the conical cap. The outside surface of the pycnometer is
wiped with a cloth. The weight of the pycnometer with wet soil
and water is taken (W3).
The contents of the pycnometer are then removed and the
pycnometer is washed thoroughly. The pycnometer is again
filled with water completely up to the hole in the conical cap.
The outside surface of the pycnometer is wiped with a cloth
and the weight of pycnometer with water is taken (W4).
9. 2.Specific Gravity:-
Specific gravity of soil solids is commonly determined by
Pycnometer method.
Procedure:-
•First take a clean, dry and empty pycnometer and take the
weight as (W1).
•Put dry soil (about one third the height) in the pycnometer
and find the weight (W2).
•Add water till the top such that the air bubbles are
completely removed and find the weight (W3).
•Empty the soil and fill water up to the top in the pycnometer
and find the weight (W4).
10.
11. 3.In-situ density/Field density:-
The field density of a natural soil deposit or of a compacted soil can
be determined by the following methods:
i. Core cutter method
ii. Sand Replacement method
iii. Water displacement method
Core cutter method:-
The apparatus consists of a mild steel cutting ring with a dolly to fit
its top and a metal hammer.
12. Cylindrical core cutter, 100 mm internal diameter & 130 mm long.
Steel rammer, mass 9 kg over all length with the foot and staff
about 900 mm.
Steel dolly, 25 mm high & 100 mm internal diameter.
Procedure:
Find the volume of core cutter by measuring its internal
dimensions.
Find the weight of the core cutter (without dolly). (W1)
Place the dolly over the cutter and drive the cutter into the
soil with the help of rammer
Take out the cutter containing soil.
Remove the dolly and trim off the excess soil above the edges of
the cutter.
Take the weight of cutter filled with soil.(W2)
Take some representative sample for water content
determination by the oven.
Repeat the test at two/three locations and find the average
density.
13. The in-situ unit weight of the soil ϒ, is found byW/V.
If the moisture content w is found, the Dry density ϒd can may be
found as ϒd = ϒ/(1+w).
Sand Replacement method:-
This method is used for the hard or gravelly soil.
The equipment consists of a sand pouring cylinder with cone,
calibrating container and a tray with a central hole.
14. In sand replacement method, a small cylindrical pit is excavated and
the weight of the soil excavated from the pit is measured. Sand
whose density is known is filled into the pit. By measuring the
weight of sand required to fill the pit and knowing its density the
volume of pit is calculated. Knowing the weight of soil excavated
from the pit and the volume of pit, the density of soil is calculated.
Therefore, in this experiment there are two stages, namely
Calibration of sand density
Measurement of soil density
15. STAGE-1 (CALIBRATION OF SAND DENSITY)
Measure the internal dimensions (diameter, d and height, h) of the
calibrating can and compute its internal volume,Vc = πd2h/4.
Fill the sand pouring cylinder (SPC) with sand with 1 cm top
clearance (to avoid any spillover during operation) and find its
weight (W1)
Place the SPC on a glass plate, open the slit above the cone by
operating the valve and allow the sand to run down. The sand will
freely run down till it fills the conical portion. When there is no
further downward movement of sand in the SPC, close the slit.
Measure the weight of the sand required to fill the cone. Let it
be W2.
Place back this W2 amount of sand into the SPC, so that its weight
becomes equal to W1 (As mentioned in point-2). Place the SPC
concentrically on top of the calibrating can. Open the slit to allow
the sand to run down until the sand flow stops by itself. This
operation will fill the calibrating can and the conical portion of the
SPC. Now close the slit and find the weight of the SPC with the
remaining sand (W3)
16. Weight of sand required to fill the calibrating container= W1 – W2
– W3 .Then this is divided by total volume of container gives unit
weight of sand.
STAGE-2 (MEASUREMENT OF SOIL DENSITY)
Clean and level the ground surface where the field density is
to be determined
Place the tray with a central hole over the portion of the soil
to be tested.
Excavate a pit into the ground, through the hole in the plate,
approximately 12 cm deep (same as the height of the
calibrating can). The hole in the tray will guide the diameter
of the pit to be made in the ground.
Collect the excavated soil into the tray and weigh the soil
(W)
17. Determine the moisture content of the excavated soil.
Place the SPC, with sand having the latest weight of W1, over
the pit so that the base of the cylinder covers the pit
concentrically.
Open the slit of the SPC and allow the sand to run into the
pit freely, till there is no downward movement of sand level
in the SPC and then close the slit.
Find the weight of the SPC with the remaining sand (W4).
Weight of sand in the pit = W1–W4–W2 and volume of sand
required to fill the pit is calculated by W1–W4–W2 /unit
weight of sand.After this we find the unit weight of soil.
18. Sieve Analysis
(For Coarse grained soils)
3.Grain Size Analysis:-
Soil in nature exists in different sizes, shapes and appearance.
Depending on these attributes, the soil at the site can be packed
either densely or loosely.
Hence it is important to determine the percentage of various
sized particles in a soil mass.
This process is called as Grain size analysis or particle size
distribution analysis.
Grain Size Analysis
Sedimentation analysis
(For fine grained soils)
19. Grain sizes:-The Indian Standard nomenclature is as follows:
GRAVEL ----- 80 mm – 4.75 mm
SAND ----- 4.75 mm – 0.075 mm
SILT ----- 0.075 mm – 0.002 mm
CLAY ----- Less than 0.002 mm
SIEVE ANALYSIS:-
This test is meant for coarse grained soils(particle size > 75µ)
which can easily pass through set of sieves.
The sieves used are 80 mm, 40 mm,
20 mm, 10 mm , 4.75 mm, 2.36 mm,
2 mm, 1 mm, 600µ, 425µ, 212µ,150µ,75µ.
The selection of the required number
of sieves is done to obtain a good particle
size distribution curve.
20. A set of IS sieves are arranged in order with one having largest
aperture at the top and that with smallest aperture at the bottom.
A lid at the top and a receiver at the bottom complete the
assembly.
A known weight of representative sample of soil is placed in the
top sieve.
The assembly is vibrated an sieve shaker for at least 10 minutes.
Depending on the particle size, soil is collected in each sieve is
measured.
21. Sedimentation Analysis:-
It is also called as wet analysis and is applicable for fine grained soils
(particle size<75µ)
The analysis is based on stokes law, which states that the velocity at
which soil particles settles in a suspension depend on shape, size and
weight of particles.
22.
23.
24. Grain size distribution curve:-
The result of the grain size analysis are usually represented in the
form of a graph named as Grain size distribution curve.
This curve is obtained from the result of sieve size analysis and it
is plotted for grain or particle size versus percentage finer.
The percentage finer is represented using normal scale and grain
or particle size is plotted in log scale.
This curve is otherwise called gradation curve.
The position, shape and a slope of a curve indicate the type of the
gradation of the soil.
Upon viewing the curve, it is possible to know whether the sand
or gravel is poorly graded or well graded.
A soil is said to be either well graded or poorly graded .A soil is
said to be well graded when it has good representation of all sizes.
On the other hand, a soil is said to be poorly graded if it has an
excess of certain particles and deficiency of other or has most of
the particles of about same size.
26. Curve-1:-Well graded soil: good representation of grain sizes over a
wide range and its gradation curve is smooth.
Curve-2:-Poorly graded soil / uniform gradation: it is either an excess
or a deficiency of certain particle sizes or has most of the
particles about the same size.
Curve-3:-Gap graded soil: In this case some of the particle sizes are
missing.
Curve-4:-Predominantly fine soil.
---For coarse grained soil, certain particle sizes such as D10 , D30 , D60
are important.
D10 represents a size in mm such that 10% of the particles are
finer than this size. It is called as Effective Size or Effective
Diameter.
Similarly D30 , D60 are grain dia corresponding to 30% and 60%
finer.
The parameters based on D-size to define grading are Coefficient
of uniformity, and coefficient of curvature.
27. Coefficient of uniformity(Cu):- Cu = D60/ D10
Cu =1 for Uniformly Graded soils/Poorly graded soil
Cu> 4 for Well graded gravel
Cu> 6 for Well graded sand
Coefficient of curvature,(Cc):- Cc= (D30)2/D10×D60
Cc lies between 1 to 3 for well graded soil.
Otherwise poorly graded soil
28. 4.Consistency Limits & Indices:-
The consistency is meant the relative ease with which soil can
be deformed.
The consistency of a fine-grained soil refers to its firmness,
and it varies with the water content of the soil.
A gradual increase in water content causes the soil to change
from solid to semi-solid to plastic to liquid states.
The water contents at which the consistency changes from one
state to the other are called consistency limits (or Atterberg
limits).
The three consistency limits/Atterberg limits are:-
1. Liquid limit
2. Plastic limit
3. Shrinkage limit
29. Liquid Limit (LL or wL ):- It is the water content at which soil
changes from a plastic to a liquid state . (OR)
It is defined as the minimum water content at which a part of a soil
is cut by a groove of standard dimensions, will flow together for a
distance of 12 mm under an impact of 25 blows in the device.
30. Liquid limit
Plastic Limit (PL or wP):- It is the water content at which soil
changes from a semi solid state to plastic state . (OR)
It is defined as the minimum water content at which the soil will just
begin to crumble when rolled into a thread of approximately 3 mm
in diameter.
Shrinkage Limit (SL or wS):- It is defined as the water content at
which the soil changes from a solid state to a semi-solid state. (OR)
It is the maximum water content at which a reduction in water
content will not cause a decrease in the volume of a soil mass.
Plastic limit
31. Consistency Indices:-
Plasticity index(PI or IP):-
It is the range of water with in which the soil exhibits plastic
properties. Hence it is the difference between liquid limit and plastic
limit.
PI or IP = (LL-PL) or (wL - wP)
Shrinkage index(SI or IS):-
It is the difference between the plastic limit and shrinkage limit of a
soil.
SI or IS = (PL-SL) or (wP - wS)
32. Liquidity index(LI or IL):-
It is the ratio of the difference between the natural water content
and the plastic limit to the plasticity index.
LI or IL = (w-PL)/PI or (w - wP)/ IP
Flow index(IF):-
It is the slope of the flow curve obtained between the number of
blows and the water content in the casagrande test for the
determination of liquid limit.
Flow curve gives an idea of shear strength variation with water
content of the soil.
33. Consistency index(IC) or Relative consistency:-
It is defined as the ratio of the difference between the liquid limit
and natural water content of a soil to its plasticity index.
IC = (wL - w)/ IP
Toughness index(IT):-
It is defined as the ratio of plasticity index to the flow index.
IT = IP/ IF
It gives an idea about the shear strength of a soil at plastic limit.
34. Activity of clays(AC):-
It is defined as the ratio of plasticity index to the percentage of clay
size particles by weight less than 2µ.
AC = IP/ % C(by weight finer than 2µ)
It is a measure of the water holding capacity of clayey soils.
It is used as an index for identifying swelling and shrinkage
characteristics.
CLAY MINERAL ACTIVITY
Kaolinite 0.38 (not have any shrinkage)
Illite 0.98
Montmorillonite >4 (have more shrinkage)
35. Sensitivity of clays(St):-
It is defined as the ratio of unconfined compressive strength of
undisturbed specimen of the soil to the unconfined compressive
strength of remoulded specimen of the same soil.
Sensitivity Classification
1 Insensitive
1-2 Little or low sensitive
2-4 Moderate or medium sensitive
4-8 Sensitive
8-16 Extra sensitive
>16 Quick sensitive
36. Shrinkage ratio(SR):-
It is defined as the ratio of a given volume change in a soil
expressed as percentage of its dry volume to the
corresponding change in water content above shrinkage limit.
V1=volume of soil mass at water content w1
V2=volume of soil mass at water content w2
Vd=volume of dry soil mass
At shrinkage limit,V2=Vd and w2=ws , hence
37. The change in water content,
Hence,
Volumetric Shrinkage (VS):-
It is defined as the decrease in the volume of a soil mass expressed
as percentage of its dry volume when the water content is reduced
from a given percentage to the shrinkage limit.
38. 5.Relative Density or Density Index(Dr or ID):-
Relative density is defined as the ratio of difference of void ratios of
cohesion less soil in its loosest state and the natural state (emax –
e) to the difference between void ratio in its loosest and densest
states (emax – emin).
39. CLASSIFICATION OF SOILS
Soil classification is the arrangement of different soils with similar
properties into groups and sub-groups based on their application.
A soil classification system represents, in effect, a language of
communication between engineers.
Any soil classification system must provide us with information
about the probable engineering behavior of soil.
Most of the soil classification systems that have been developed
for engineering purposes are based on simple index properties
such as particle-size distribution and plasticity.
For general engineering purposes, soil may be classified by the
following systems:
1. Particle size classification
2. Textural classification
3. Highway Research Board classification
4. Unified Soil classification
5. IS Soil classification system
41. INDIAN STANDARD CLASSIFICATION SYSTEM:-
The ISCS classifies the soils into 18 groups.
Soils are broadly divided into three divisions:
1. Coarse grained soil
In these soils, more than half the total material by mass is larger
than 75 microns IS sieve.
2. Fine grained soil
In these soils, more than half the material by mass is smaller than
75 microns IS sieve.
3. Highly organic soils and other miscellaneous soil materials
These soils contain large percentages of fibrous organic matter,
such as peat, and the particles of decomposed vegetation.
42.
43.
44.
45. STEP BY STEP PROCEDURE OF IS CLASSIFICATION OF SOILS:-
A step-by-step procedure for classifying the soils as per IS :1498 -1970 is
illustrated below
1. Determine whether the given soil is of organic origin or coarse-grained or
fine-grained. An organic soil is identified by its colour (brownish black or
dark) and characteristic odour. If 50 % or more of the soil by weight is
retained on the 75 µ sieve, it is coarse-grained, if not, it is fine-grained
2. If the soil is coarse-grained
(a) Obtain the GSD curve from a sieve-analysis. If 50 % or more of the
coarse fraction (>75 µ) is retained on the 4.75 mm sieve, classify the soil
as gravel (G); if not, classify it as sand (S)
(b) If the soil fraction passing through the 75µ sieve is less than 5 %,
determine the gradation of the soil by calculating Cu and Cc from the
GSD curve. If well graded (according to the criteria laid down), classify the
soil as GW or SW; if poorly graded, classify as GP or SP
(c) If more than 12 % passes through the 75 mm sieve, perform the liquid
limit and plastic limit tests on the soil fraction passing though the 0.425-
mm sieve. Use the LS. plasticity chart to determine the classification (GM,
SM, GC, SC, GM - GC or SM SC)
46. (d) If between 5 % and 12 % passes through the 75 mm sieve, the soil is
assigned a dual symbol appropriate to its gradation and plasticity
characteristics. (GW-GM, GW-GC, GP-GC, GP-GM, SW-SM, SW-SC, SP-
SC, SP-SM)
3. If the soil is fine-grained (inorganic)
(a) Determine WL and Wp on the minus 0,425 mm sieve fraction and
determine the plasticity index 0.425 mm sieve
(b) If the limits plot below the A line, classify as silt (h M)Further, if w, is
less than 35, classify as ML: if wL between 35-50, classify as MI; if wL is
greater than is an 50, classify as MH.
(c) If the limits plot above the A - 1 line, classify as clay C. Assign the group
symbol CL or Cl or CH, depending the value of liquid limit, as in (b).
(d) If the limits plot in the hatched zone, classify as CL-ML. If the limits plot
close to the A - line or close to wL = 35 %or w= 50 % lines, assign dual
symbols as outlined earlier
4. If the soil is of organic origin, the plasticity chart is used after determining
wL and wP and the soil classified as OL, OI or OH
47.
48. REFERENCE:-
Google
Soil Mechanics and Foundations:
By B.C. Punmia, Ashok Kumar Jain, Arun Kumar Jain
Basic and Applied Soil Mechanics:
By Gopal Ranjan, A.S.R. Rao
Geotechnical Engineering:
By C.Venkatramaiah
