government engineering college, dahod applied mechanics
TRANSCRIPT
Government Engineering College, Dahod
Applied Mechanics Department
Laboratory Manual
of
Geotechnical Engineering (3130606)
B.E. - II, Sem. – 3
Prepared By
Dr. Yogendra Tandel
Prof. Nirav Umravia
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Date:
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Index
Expt.
No. Experiment Title
Page
No.
Assign
Date
Check
Date Signature
1 Field Density by Core Cutter Method 1
2
Field Density by Sand Replacement
Method
4
3 Sieve analysis 7
4 Liquid and Plastic Limit 10
5 Shrinkage Limit 14
6 Permeability Tests 16
7 Proctor Compaction Test 21
8 Consolidation/Oedometer test 24
9 Direct Box Shear Test 30
10 Unconfined Compression Test 36
11 Triaxial Compression Tests 39
12 Laboratory Vane Shear Test 44
13 Standard Penetration Test (SPT) 47
14 California Bearing Ration (CBR) Test 52
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 1
EXPERIMENT 1
FIELD DENSITY BY CORE CUTTER METHOD
AIM
To determine the field bulk density and dry density of soil by core cutter method at the given location.
APPARATUS
Cylindrical Core cutter, dolly, rammer, straight edge knife, Non-corrodible metal container,
thermostatically controlled oven, weighing balance (Triple Beam Balance), Shovel.
THEORY
Bulk Density
It is the ratio of total weight of the solid mass of soil to the volume of soil mass. It is denoted by
𝛾 = 𝑊
𝑉 g/cc
where, W = Total weight of soil mass & V = Total Volume of soil mass.
Dry Density
The dry density is the weight of solids per unit of total volume of the soil mass.
𝛾𝑑 = 𝑊𝑑
𝑣
Relation between 𝛾, 𝛾𝑑, 𝑤
𝛾𝑑 = 𝛾
1 + 𝑤
Core Cutter Method
A core cutter consisting of a steel cutting edge at the bottom, 10 cm in diameter and about 13 cm high
and with 2.5 cm high dolly attachment is driven vertically in the cleaned surface at the location with
the help of rammer, till about 1 cm of the dolly remains above the surface. The cutter containing the
soil is dug out of the ground, the dolly is removed, and excess soil is trimmed off. The weight of the
empty core cutter and its volume being known, by dividing the weight of soil by the volume of the
cutter the bulk density is determined. The water content of the excavated soil is found in the laboratory
using soil sample taken from top, bottom, and centre of the core cutter and the dry density is computed
using the relation;
𝛾𝑑 = 𝛾
1 + 𝑤
Figure 1.1: Core cutter apparatus
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 2
APPLICATION
❖ The in-situ density of soil is an important property having many applications in soil engineering. In
practical problems associated with earthworks and foundations, the weight of the soil itself exerts
forces which have to be taken into account in the analysis. It is therefore necessary to know the bulk
density of the soil, form which these forces can be calculated.
❖ For calculations of void ratio and saturation, important factors relating to compaction of soil.
❖ To determine the field density of soil through which the field bearing capacity of soil can be found
e.g. for the engineering structures like railways embankments, dams, road embankments etc.
PROCEDURE
❖ Measure the inside diameter of cutter, its length and then calculate its volume.
❖ Weigh the Core Cutter without dolly.
❖ Clean the top soil on the site, level it.
❖ Put the dolly on the core cutter and ram it in to the soil completely so that it is vertical throughout
the driving procedure.
❖ Dig out the core cutter containing soil, from the ground carefully not disturbing the core.
❖ Weight the cutter full of soil after levelling it.
❖ Remove the soil core from the cutter. Keep the representative samples for water content
determination, the sample being taken from the top, bottom, & centre of the core.
OBSERVATION DATA
Core Cutter No. 1 2 3
Empty Weight of Core
Cutter (W1)
Inner Diameter of Core
Cutter
Height of Core Cutter
Volume of Core Cutter
OBSERVATION TABLE
Core Cutter
No.
Wt. of Core
cutter +
Soil:
W2 (g)
Wt. of
soil:
W3 = W2-
W1 (g)
Bulk
Density:
𝛾 = 𝑊3
𝑉
(g/cc)
Moisture
content:
w (%)
Dry
Density:
𝛾𝑑 = 𝛾
1 + 𝑤
(g/cc)
Average
Dry
Density
Container
No.
Wt. of
empty
container:
W1 (g)
Wt. of
container
+ Wet
soil: W2
(g)
Wt. of
container
+
Dry soil:
W3 (g)
Wt. of
Water:
W4 = W2
– W3 (g)
Wt. of dry
soil: W5
= W3-W1
(g)
Water
Content:
𝑤 =
𝑊4
𝑊5×
100 (%)
Average
Water
Content
(%)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 3
CALCULATION
RESULT
The bulk density of given soil at the location of sampling is =________ gm/cc and density of soil =
_______ gm/cc & water content = ______%.
CONCLUSION
REFERENCE
IS: 2720-Part 29, 1975: Methods of Test for Soils, Part 29: Determination of Dry Density of Soils In-
place by the Core-cutter Method.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 4
EXPERIMENT 2
FIELD DENSITY BY SAND REPLACEMENT METHOD
AIM
Determine the in situ density of natural or compacted soils using sand pouring cylinders.
APPARATUS
Sand pouring cylinder of 3 litre/16.5 litre capacity, mounted above a pouring come and separated by a
shutter cover plate, Tools for excavating holes; suitable tools such as scraper tool to make a level
surface, Cylindrical calibrating container with an internal diameter of 100 mm/200 mm and an internal
depth of 150 mm/250 mm fitted with a flange 50 mm/75 mm wide and about 5 mm surrounding the
open end, Balance to weigh unto an accuracy of 1g., Metal containers to collect excavated soil, Metal
tray with 300 mm/450 mm square and 40 mm/50 mm deep with a 100 mm/200 mm diameter hole in
the centre, Glass plate about 450 mm/600 mm square and 10mm thick, uniformly graded natural sand
passing through 1.00 mm I.S.sieve and retained on the 600micron I.S.sieve. It shall be free from
organic matter and shall have been oven dried and exposed to atmospheric humidity.
PROCEDURE
❖ Fill the sand pouring cylinder with clean sand so that the level of the sand in the cylinder is within
about 10 mm from the top. Find out the initial weight of the cylinder plus sand (W1) and this weight
should be maintained constant throughout the test for which the calibration is used.
❖ Allow the sand of volume equal to that of the calibrating container to run out of the cylinder by
opening the shutter, close the shutter and place the cylinder on the glass sand takes place in the
cylinder close the shutter and remove the cylinder carefully. Weigh the sand collected on the glass
plate. Its weight (M2) gives the weight of sand filling the cone portion of the sand pouring cylinder.
Repeat this step at least three times and take the mean weight (M2) Put the sand back into the sand
pouring cylinder to have the same initial constant weight (M1).
❖ Determine the volume (V) of the container be filling it with water to the brim. Check this volume
by calculating from the measured internal dimensions of the container.
❖ Place the sand poring cylinder centrally on yhe of the calibrating container making sure that constant
weight (M1) is maintained. Open the shutter and permit the sand to run into the container. When no
further movement of sand is seen close the shutter, remove the pouring cylinder and find its weight
(M3).
❖ Approximately 60 sq cm of area of soil to be tested should be trimmed down to a level surface,
approximately of the size of the container. Keep the metal tray on the level surface and excavate a
circular hole of volume equal to that of the calibrating container. Collect all the excavated soil in the
tray and find out the weight of the excavated soil (Mw). Remove the tray, and place the sand
pouring cylinder filled to constant weight so that the base of the cylinder covers the hole
concentrically. Open the shutter and permit the sand to run into the hole. Close the shutter when no
further movement of the sand is seen. Remove the cylinder and determine its weight (M3).
❖ Keep a representative sample of the excavated sample of the soil for water content determination.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 5
OBSERVATIONS AND CALCULATIONS
Sr.
No. Observation and calculation Determination
Observation 1 2 3
1 Volume of calibrating
cone(Vc)
2 Mass of pouring
cylinder(M1),filled with sand
3 Mass of cylinder after pouring
sand into calibrating container and cone(M3)
4 Mass of sand in the cone(M2)
Calculations
5 Mass of sand in the calibrating
container
Mc=(2)-(3)-(4)
6 Dry density of sand ρ s =Mc/Vc
Sr.
No
Observations and
Calculations
Determination
Observation 1 2 3
1 Mass of excavated soil(M)
2 Mass of pouring cylinder(M1),
filled with sand
3
Mass of pouring cylinder after
pouring into the hole and cone
(M4)
Calculations
4. Mass of sand in the hole
Ms=M1-M4-M2
5 Volume of sand in the hole,
V=Ms/ρs
6 Bulk Density,ρ=M/V
7 Water content,w
8 Dry Density=ρ/(1+w)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 6
Container
No.
Wt. of
empty
container:
W1 (g)
Wt. of
container
+ Wet soil:
W2 (g)
Wt. of
container
+ Dry soil:
W3 (g)
Wt. of
Water:
W4 = W2
–W3 (g)
Wt. of
Dry soil:
W5 = W3 –
W1 (g)
Water
Content : w =
W4 * 100%
W5
Average
Water
Content
%
RESULT
CONCLUSION
REFERENCE
IS: 2720-Part 28, 1974: Methods of test for soils, Part 28: Determination of dry density of soils, in-
place, by the sand replacement method.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 7
EXPERIMENT 3
SIEVE ANALYSIS
AIM
To determine particle size distribution of a given soil sample by using dry sieve analysis method.
APPARATUS
Mechanical sieve shaker, Set of different size of sieves i.e. 4.75 mm, 2.0 mm, 1.0 mm, 0.600mm,
0.425mm, 0.300mm, 0.212mm, 0.150mm, 0.075mm, Triple Beam Balance
THEORY
Particle Size Distribution
The percentage of various sizes of particles in a given dry soil sample is found by a particle size
analysis or mechanical analysis. The mechanical analysis is performed in two stages: Sieve Analysis,
Sedimentation Analysis
(i) Sieve Analysis
In BS and ASTM standards the sieves are given in terms of the number of openings per inch. In the
Indian Standards, the sieves are designated by the size of the aperture in mm. The complete sieve
analysis can be divided into two parts the coarse analysis and the fine analysis.
An oven dried sample of soil is separated in to two fractions by sieving it through a 4.75mm IS
sieve. The portion retained on it is termed as the gravel fraction and is kept for the coarse analysis,
while portion passing through it is subjected to fine sieve analysis. The following sets of sieves are
used for coarse sieve analysis IS: 100 mm, 63 mm, 20 mm, 10 mm, & 4.75 mm. The sieves used for
fine sieve analysis are 2.0 mm, 1.0 mm, 0.600, 0.425, 0.300, 0.212, 0.150 & 0.075 mm.
(ii) Sedimentation Analysis
This analysis is based on “Stokes Law” i.e. “velocity of setting of particles depends on size of
particles” with the assumption that the soil particles are spherical and have the same specific gravity,
the coarser particles settle more quickly than the finer ones.
Hydrometer &/or Pipette Method is used for silt and clay (i.e. passing 0.075 mm sieve). According to
this law, the velocity with which a grain settles down in suspension, all other factors being equal is
dependent upon the shape, weight, & size of the grains.
Types of soils based on particle size distribution:
❖ Well Graded Soil: A soil is considered to be well graded when there is a good representative of all
the particles size from largest to smallest.
❖ Poorly Graded Soil: A soil is considered to be poorly graded if there is an excess of a particle size
within the limits of the maximum and minimum sizes.
❖ Uniformly Graded Soil: If most of the particles are of about the same size, such a soil is called
uniformly graded soil.
❖ Gap Graded Soil: A soil is considered to be gap graded if there is absence of one or two sizes of
particles within the limits of maximum & minimum sizes.
Particle Size Distribution Curve
The results of the mechanical analysis are plotted to get a particle size distribution curve with the
percentage finer N as the ordinate and the particle diameter as the abscissas, the diameter being plotted
on the logarithm scale. A particle size distribution curves gives us an idea about the type and gradation
of the soil.
For coarse grained soil, certain particle sizes such as D10, D30, and D60 are important. Dn
represents a size in mm such that n is the percentage of the particles finer than this size. D10 is
sometimes called the effective size or effective diameter of the soil under consideration. The co-
efficient of uniformity is a measure of particle size range.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 8
Similarly, the shape of the particle size curve is represented by the coefficient of the curvature Cc
given by
For a uniformly graded soil, Cu is nearly unity. For a well graded soil, Cc must be 1 to 3 and in
addition Cu must be greater than 4 for gravels and 6 for sands.
APPLICATION
❖ The analysis of soil by particle size provides a useful engineering classification system for soil.
❖ Identification of soil type i.e. sample is well graded, uniformly graded, poorly graded or gap
graded.
❖ For selection of filter material, core material etc. in case of earthen dam, sieve analysis is very
useful.
❖ In case of concrete mix design it is very much useful to achieve the required grade of concrete.
❖ In the design of gravel pack at tube wells, type of aquifer material can identify through sieve
analysis and thereby best selection of gravel pack against filler or screen can be possible.
PROCEDURE
❖ Take 1 kg of dry representative soil sample.
❖ Sieve the same through all the sieves successively in the descending order of apertures sizes with the
largest at top. The sieving in each sieve should be done up to 10 minutes.
❖ The shaking of sieve during sieve analysis should be done in all directions. This can be done
manually or by mechanical sieve shaker.
❖ Weigh & record the material retained in each sieve as shown in observation table. An error of 1%
loss in the soil sample is allowed but no increase in the total weight shall be allowed. This 1 % error
is then adjusted in all the reading proportionately.
❖ The result of sieve analysis is plotted as particle size distribution curve representing particle
size on logarithmic scale and percent finer on the arithmetic scale.
OBSERVATION DATA
❖ Weight of soil taken for sieve analysis =
OBSERVATION TABLE
Sieve Size Weight
Retained
Percentage
Weight
Retained
Cumulative
Percentage
Retained
Percentage Finer
(100 – Cumulative
Percentage
Retained)
4.75 mm
2.0 mm
1.0 mm
0.600 mm
0.425 mm
0.300 mm
0.212 mm
0.150 mm
0.075 mm
Pan
Total
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 9
CALCULATION
RESULT
❖ D10 =
❖ D30 =
❖ D60 =
❖ Co-efficient of uniformity =
❖ Co-efficient of Curvature =
❖ % Coarse Sand =
❖ % Medium Sand =
❖ % Fine Sand =
❖ % Silt & Clay (< 75 size) =
CONCLUSION
REFERENCE
IS 2720-Part 4, 1985: Methods of test for soils, Part 4: Grain size analysis.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 10
EXPERIMENT 4
LIQUID AND PLASTIC LIMIT
AIM
To determine liquid limit and plastic limit of the given soil sample.
APPARATUS
Standard Casagrande’s mechanical liquid limit device consisting of a brass cup and carriage mounted
on a rubber base of B. S. hardness 21 to 25 with 1 cm cup drop, Casagrande’s & ASTM grooving
tools, flat glass plate, Triple Beam Balance, Thermostatic controlled oven, water content container, rod
of 3mm diameter.
THEORY
Consistency is a measure of the relative ease with which the soil can be deformed. This term is
mostly used for fined grained soils for which the consistency is related to a large extent to water
content. Consistency thus denoted by the state of soil after mixing it with water which may be
termed as soft, firm, stiff & hard. Atterberg divided the entire range from liquid to solid state in to
four stages; Liquid State, Plastic State, Semi-Solid State, Solid State.
He set arbitrary limits, known as consistency limit or Atterberg’s limits for these divisions in terms of
water content. Thus, the consistency limits are the water contents at which the soil mass passes from
one state to the next.
Liquid Limit
Liquid limit is the water content corresponding to the arbitrary limit between liquid and plastic state
of consistency of soil. It is defined as the minimum water content at which the soil is still in liquid
state, but has a small shearing strength against flowing which can be measured by Casagrande’s
apparatus.
Plastic Limit
Plastic limit is the water content corresponding to an arbitrary limit between the plastic and
semi-solid states of consistency of a soil. It is defined as the minimum water content at which the soil
has just began to crumble when rolled into a thread approximately 3mm in diameter.
Shrinkage Limit
Shrinkage limit is defined as the maximum water content at which any further reduction in
water content will not cause a decrease in the volume of soil mass. It is the lowest water content at
which a soil can still remain completely saturated.
Plasticity Index
The range of consistency within which a soil exhibits plastic properties is called plastic range
and is indicated by plasticity index. The plasticity index is defined as the numerical difference between
liquid limit & plastic limit.
Consistency Index (Ic)
The consistency index or the relative consistency is defined as the ratio of the liquid limit minus the
natural water content to the plasticity index of a soil and given as
where w = natural water content of the soil.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 11
Consistency index is useful in the study of the field behaviour of saturated fine grained soil. A
negative consistency index indicates that the soil has natural water content greater than the liquid limit
and hence behaves just like a liquid.
Liquidity Index (IL)
The liquidity index or water plasticity ratio is the ratio, expressed as a percentage, of the natural
water content of a soil minus its plastic limit, to its plasticity index.
Flow Index
The relation can determine the slope of the curve also known as flow index.
Toughness Index (IT)
The toughness index is defined as the ratio of the plasticity index to the flow index.
APPLICATION
❖ The liquid and plastic limits provide the most useful way of identifying and classifying the fine
grained cohesive sols.
❖ Clay particles are too small to be examined visually, but the Atterberg’s limits enable clay soils to
be classified physically, and the probable type of minerals to be assessed.
❖ The Atterberg’s limits may be used to correlate soil strata occurring in different areas of a site, or
to investigate in detail the variation of soil properties which occur within a limited zone.
❖ For most straight forward applications it is possible to obtain sufficient understanding of
the nature of clay soil from Atterberg’s limits and moisture content tests, and little else , if the
geological history of the soil is also known.
PROCEDURE
Determination of Liquid Limit
❖ Take a dry soil sample passing through 0.425 mm I.S. Sieve and place it on a glass plate and add
water enough to form a hard paste of uniform consistency, by mixing them thoroughly. Keep it for
some time covered with a moist cloth to mature.
❖ Fill half the cup with the paste symmetrically leveled horizontally with the help of spatula so that it
can be parallel to the curvature of cup and depth of soil in cup is equal to 1 cm.
❖ Divide the paste in the cup by means of a grooving tool along the cup diameter through centre taking
care that tool is leveled normal to the surface.
❖ Now, the handle of the apparatus is turned at the rate of 2 revolutions per second, until two parts of
soil come in contact at the bottom parts of divided soil cake along a distance of at least 10mm.
❖ Now the representative slice of soil sample is collected and taken for water content determination.
❖ Now the entire procedure is carried out again by changing the consistency of mix by adding water
&/or leaving the soil paste to dry.
❖ 5 to 6 reading on either side of 25 blows i.e. 2 to 3 readings on consistency side taking more than 25
blows, & 2 to 3 reading on consistency side taking less than 25 blows but within the range of 15 to
40 blows.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 12
Determination of Plastic Limit
❖ Take some quantity of dry soil sample passing 0.425 mm and mix it with some quantity of distilled
water on a glass plate, sufficient to make it plastic enough to be shaped into a ball. Keep the plastic
soil for maturing for about 10 to 15 minutes.
❖ Take about 8 grams of matured soil and a ball is made out of it and is then rolled on a flat plate with
hand applying sufficient pressure to make it a thread of 3mm uniform diameter. Repeat this
procedure until this 3 mm diameter uniform thread starts crumbling.
❖ The threads are collected in a container and then kept for water content determination.
OBSERVATION TABLE
For Liquid Limit
No. of
Blows
Container
No.
Wt. of empty
Container (g)
Wt. of container
+ Wet soil (g)
Wt. of container
+ Dry soil (g)
Water content
(%)
For Plastic Limit
Container
No.
Wt. of empty
Container (g)
Wt. of container
+ Wet soil (g)
Wt. of container
+ Dry soil (g)
Water content
(%)
Average
Plastic
Limit
CALCULATION
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 13
RESULT ❖ Liquid Limit =
❖ Plastic Limit =
❖ Plasticity Index =
CONCLUSION
REFERENCE
IS: 2720, Part-5, 1985: Methods of test for soils, Part 5: Determination of liquid and plastic limit.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 14
EXPERIMENT 5
SHRINKAGE LIMIT TEST
AIM
To determine the shrinkage limit of the soil sample.
APPARATUS
Mercury, Glass plate, Oven, Balance with 0.01 g sensitivity, Evaporating dish, Spatula, Glass cup,
Shrinkage dish, Desiccator.
THEORY
Shrinkage limit is the maximum water content at which a reduction in water content will not cause
decrease in the volume of the soil mass. It is therefore the lowest water content at which a soil can still
be completely saturated. It is the boundary semi-solid and solid states.
PROCEDURE
❖ Mix about 50 g of soil passing through 425 micron sieve with distilled water, to make a creamy
paste which can be placed in the shrinkage dish without any air voids. The required mixing water
content is somewhat greater than the liquid limit.
❖ Coat a thin layer of vase line or grease inside of the shrinkage dish and then weigh.
❖ Fill the dish in three layers by placing soil paste about one third the capacity of the dish at a
time and tapping the dish gently on a firm surface so that the soil flows to the edges. The firm
surface should be properly cushioned by a rubber sheet. The last layer should stand a little
above the rim and care should be taken not to trap air within the soil. Strike off the excess soil in
level with the top of dish and clean the dish on its outside.
❖ Weigh the dish full of wet soil immediately. Allow it to dry in air until the color of soil pat
turns light. Then dry in an oven at 105° to 110°c. Cool the dish with dry soil pat in a desiccator and
weigh.
❖ Remove the dry pat from dish, clean and dry the shrinkage dish and determine its empty mass.
❖ Weigh the empty mercury-weighing dish also.
❖ Keep the shrinkage dish in the large porcelain or stainless steel dish, fill it to overflowing with
mercury and remove the excess by pressing the plain glass plate firmly over the top of the dish,
taking care that no air entraps. Transfer the contents of the shrinkage dish to the mercury weighing
dish and weigh to an accuracy of 0.1 g. Then divide this mass by density of mercury to obtain the
volume (V1) of the shrinkage dish.
❖ Place the glass cup in a large dish, fill to over flowing with mercury and remove the excess by
❖ pressing the glass plate, with prongs firmly over the top of the cup. Wipe off any mercury adhering
on the side and then place the cup full of mercury to another large dish.
❖ Place the dry soil pats on the surface of mercury and submerge it under the mercury by pressing
with the glass plate with prongs (Figure 5.1), taking care that no air entraps.
❖ Transfer the mercury displaced by the dry pat to the mercury weighing dish and weigh. Record the
observations and calculate shrinkage limit.
Figure .1: Determination of shrinkage limit
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 15
OBSERVATION TABLE
Density of mercury: 𝜌𝑚 (g/cc) =
Mass of shrinkage dish: M1 (g) =
Mass of shrinkage dish + Wet soil: M2 (g) =
Mass of the wet soil in shrinkage dish: M (g) = M2 - M1 =
Mass of the shrinkage dish + Dry soil: M3 (g) =
Mass of dry soil pat: Ms (g) = (M3 - M1) =
Mass of mercury in the shrinkage dish: Mm (g) =
Volume of the wet soil = Volume of the shrinkage dish: V1 (cc) = Mm𝑚 /𝜌
Mass of the mercury displaced by dry soil pat: Md (g) =
Volume of dry soil pat: V2 (cc) = Md/13.6
Shrinkage limit = (𝑀−𝑀𝑠)𝜌𝑤−(𝑉1−𝑉2)
𝑀𝑠=
CALCULATION
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part-6, 1972: Methods of test for soils, Part 6: Determination of shrinkage factors.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 16
EXPERIMENT 6
PERMEABILITY TESTS
AIM
To determine the co-efficient of permeability of given soil sample in the laboratory by performing
suitable permeability test depending on the soil type.
APPARATUS
Soil sample, permeameter with all accessories, balance to weigh up to 1g accuracy, 4.75mm and 2
mm I.S. Sieve, mixing pan, basin, stop watch, graduated measuring cylinder, meter scale, beaker,
and thermometer.
THEORY
Permeability
It is defined as the property of a porous material which permits the passage or seepage of
water (or other fluids), through inter-connected voids.
Coefficient of Permeability
It is defined as the average velocity of flow that will occur through the total cross-sectional area of soil
under unit hydraulic gradient. The dimensions of coefficient of permeability (k) are the same as those
of velocity. It is usually expressed as cm/sec or
m/day.
Darcy’s Law
The law of flow of water through soil was first studied by Darcy who demonstrated
experimentally that for laminar flow conditions in a saturated soil, the rate of flow or the discharge
per unit time is proportional to the hydraulic gradient.
where; q = discharge per unit time, A = total cross-sectional area of soil mass perpendicular to
direction of flow, i = hydraulic gradient, k = Darcy’s coefficient of permeability, v = velocity of flow
If a soil sample of length l and cross-sectional area A, is subjected to differential head of water, h1 –
h2, the hydraulic gradient will be equal to (h1 – h2)/l and we have
Constant Head Test
Figure shows the diagrammatical representation of constant head test. Water flows from the overhead
tank consisting of three tubes i.e. the inlet tube, the overflow tube and the outlet tube. The constant
hydraulic gradient i causing the flow is the head h (i.e. difference in the water levels of the overhead
and bottom tanks) divided by the length L of the sample. If the length of the sample is large, the head
lost over a length of specimen is measured by inserting piezometric tubes as shown in the figure. If Q
is the total quantity of flow in a time interval t, we have from Darcy’s law,
When steady state of flow is reached, the total quantity of water Q in time t collected in a measuring
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 17
jar and value of permeability found out using the following relation
Falling Head Test
The constant head test is used for coarse grained soil only where a reasonable discharge can be
collected in a given time. However, the falling head test is used for relatively less permeable soils
where the discharge is small. Figure shows the diagrammatical representation of a falling head test
arrangement.
A stand pipe of known cross sectional area a is fitted over the permeameter, and water is
allowed to run down. The water level in the stand pipe constantly falls as water flows. Observations
are started after a steady state of flow has reached. The head at any time instant t is equal to the
difference in the water level in the stand pipe and the bottom tank. Let h1 and h2 be heads at time
intervals t1 and t2 (t2 > t1) respectively. Let h be the head at any intermediate time interval t, and –
dh be the change in the head in a smaller time interval dt (minus sign has been used since h decreases
as t increases). Hence, from Darcy’s Law, the rate of flow q is given by
where i = hydraulic gradient at time t = h/L
Permeability is given by
APPLICATION
❖ Estimation of quantity of water likely to flow into an excavation, and hence the pumping capacity to
be provided. ❖ To know whether groundwater lowering is feasible.
❖ Design of sheet pile walls, and the depth to which they need to be extended.
❖ Prevention of boiling or heave of sand strata or any non cohesive soil at the bottom of
excavation below the water table.
❖ To estimate the quantity of seepage flow through filters zones so as to provide adequate drainage
capacity, as well as to prevent development of excessive
o seepage pressures.
❖ For calculation of seepage pressures from flow net analysis, which in turn affect the stability
of earth structures. ❖ Drainage of highway and airfield bases and sub-bases.
❖ Estimation of the yield of water and the rate of extraction from aquifers.
❖ Design of graded filters.
PROCEDURE
Preparation of Statically Compacted Remoulded Specimen
❖ For the given volume (V) of the mould, calculate the mass (M) of the soil mix so as to give the
desired dry density (γd).
❖ Take content is raised to the required water content for the soil determined by Proctor’s test. If
permeability is to be determined at any other dry density, raise the water content of the soil to the
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 18
desired value. Leave the soil mix for some time in air tight container.
❖ Assemble permeameter for static compaction. For this, attach the 3 cm collar to the bottom end of
the 0.3 liter mould and 2.5 cm collar to it s top end. Support the mould assembly over the 2.5 cm end
plug with the 2.5 cm collar resting on the split collar kept around the 2.5 cm end plug. The 0.3 litre
mould should be lightly greased form inside.
❖ Put the weighed quantity of soil into the mould assembly. Insert the top 3 cm end plug into the top
collar. The soil may be tamped with hand while being poured into the mould. Keep the entire
assembly into a compression machine and remove the split collar. Apply compressive force on the
assembly till the flanges of both the end plugs touch the corresponding collars.
❖ Maintain the load for about 1 minute and then release it. Remove the top 3 cm plug and collar. Place
a filter paper or fine wire gauge on the top of the specimen and fix the porous stone on it.
❖ Turn the mould assembly upside down and remove the 2.5 cm end plug and collar. Place the top
perforated plate on the top of the soil specimen and fix the top can on to it, after inserting the sealing
gasket.
Saturation of Compacted Specimen
❖ To saturate the compacted specimen, place the permeameter mould in the vacuum desiccator and
open air release valve. Fill the desiccator with de-aired water till the water level reaches well above
the top cap and the water inlet nozzle is submerged.
❖ Apply vacuum of about 5 to 10 cm of mercury and maintain it for some time.
❖ Increase this vacuum slowly in steps, to about 70 cm of mercury.
❖ In every increment, sufficient time should be given so that the air bubbles come out without vibrating
the specimen.
❖ Take out specimen when the saturation is complete.
Constant Head Test
❖ Place the mould assembly in the bottom tank and fill the bottom tank with water upto its outlet.
❖ Connect the outlet tube of the constant head tank to the inlet nozzle of the permeameter, after
removing the air in the flexible rubber tubing connecting the tube. Adjust the hydraulic head by
either adjusting the relative heights of the permeameter mould and the constant head tank, or by
raising of lowering the air intake tube within the head tank.
❖ Start the stop watch, and at the same time put a beaker under the outlet of the bottom tank. Run the
test for some convenient time interval. Measure the quantity of water collected in the beaker during
that time or for a fixed quantity of water in the measuring cylinder note the time required to collect it.
❖ Repeat the test twice more, under the same head and for the same time interval.
Falling Head Test
❖ Prepare the mould with soil specimen in the permeameter and saturate it as explained above. Kee the
permeameter mould assembly in the bottom tank and fill the bottom tank with water upon its outlet.
❖ Connect the water inlet nozzle of the mould to the stand pipe filled with water. Permit water to flow
for some time till steady sate of flow is reached.
❖ With the help of the stop watch, note the time interval required for the water level in the stand pipe to
fall from some convenient initial value to some final value.
❖ Repeat the above step at least twice and determine the time for the water level in the stand pipe to
drop from the same initial head to the same final value.
❖ In order to determine the inside area of cross section of the stand pipe, collect the quantity of water
contained in between two graduations of know distance apart. Find the mass of this water accurate to
0.1 gm. The mass in grams divided by the distance in cm, between the two graduations will give the
inside area of cross section of the stand pipe in sq. cm.
OBSERVATION DATA (CONSTANT HEAD TEST) ❖ Moulding Water Content (w) =
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 19
❖ Dry Density (γd) =
❖ Specific Gravity (G) = ❖ Void Ratio =
❖ Room Temperature =
❖ µ27 =
❖ µrt (from table) =
❖ Diameter of Sample = ❖ Height of Sample =
❖ Cross Sectional Area of Sample =
❖ Head Causing Flow of Water =
OBSERVATION TABLE
Quantity of
Water Collected:
Q (cm3)
Time Required to
Collect Q i.e. t
(seconds)
Coefficient of
Permeability
Avg. Coefficient
of Permeability:
k (cm/sec)
OBSERVATION DATA (FALLING HEAD TEST)
❖ Moulding Water Content (w) =
❖ Dry Density (γd) =
❖ Specific Gravity (G) = ❖ Void Ratio =
❖ Room Temperature =
❖ µ27 =
❖ µrt (from table) =
❖ Diameter of Sample = ❖ Height of Sample =
❖ Cross Sectional Area of Sample =
❖ Diameter of Stand Pipe =
OBSERVATION TABLE
Hydraulic Head Time Required
I.R.:
h1
(cm)
F.R.:h2
(cm)
Diff.
in
cm
Initial
Cloc
k
Time
:t1
Final
Cloc
k
Time
: t2
Time
t
in
sec.
(t1 –
t2) x
60
Coefficient
of
Permeability
k in cm/sec
Average
Coefficient
of
Permeability
k in
cm/sec
CALCULATION
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 20
RESULT
For Constant Head Test
❖ Coefficient of Permeability krt =
❖ Coefficient of Permeability k27 =
For Falling Head Test
❖ Coefficient of Permeability krt =
❖ Coefficient of Permeability k27 =
CONCLUSION
REFERENCE
IS: 2720, Part-17, 1986: Methods of test for soils, Part 17: Laboratory determination of permeability.
Viscosity of Water (From International Critical Tables)
Temperature
oC
Viscosity
(poise)
Temperature
oC
Viscosity
(poise)
Temperature
oC
Viscosity
(poise)
4 0.01568 18 0.01060 32 0.00767
5 0.01519 19 0.01034 33 0.00751
6 0.01473 20 0.01009 34 0.00736
7 0.01429 21 0.00984 35 0.00721
8 0.01387 22 0.00961 36 0.00706
9 0.01348 23 0.00938 37 0.00693
10 0.01310 24 0.00916 38 0.00679
11 .001274 25 0.00895 39 0.00666
12 0.01239 26 0.00875 40 0.00654
13 0.01206 27 0.00855 41 0.00642
14 0.01175 28 0.00836 42 0.00630
15 0.01145 29 0.00818 43 0.00618
16 0.01116 30 0.00800 44 0.00608
17 0.01088 31 0.00783 45 0.00597
* For intermediate temperatures, the value of viscosity can be interpolated.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 21
EXPERIMENT 7
PROCTOR COMPACTION TEST
AIM
To determine maximum dry density and optimum moisture content of given soil sample using standard
proctor test.
APPARATUS
Standard proctor mould, Standard proctor rammer of weight 2.5 kg having a fall of 30.5 cm, Tray, 2.5
kg oven dry soil sample (passing 4.75 mm sieve), Fiber hammer, Knife, Triple beam balance,
Thermostatic controlled oven, Oil, Measuring cylinder, Non corrodible water content container.
THEORY
Compaction
It is the process during which the soil particles are artificially rearranged and packed together into a
closer state of contact by mechanical means in order to decrease the porosity of the soil and thus
increasing its dry density. The compaction process may be accomplished by rolling, tamping, or
vibration. An example of compaction is reduction in voids produced in a layer of the sub-grade by a
rubber tyre or steel tyre roller during road construction.
Optimum Water Content
A definite relationship between the soil water content and degree of compaction measured as dry
ensity to which a soil might be compacted, and that for a specific amount of compaction energy pplied
on soil, this water content is termed as Optimum Water Content.
Zero Air Void Line
A line which shows the water content dry density relation for the compacted soil containing a constant
percentage air voids is known as air voids line and is given by the following equation;
𝛾𝑑 =(1 − 𝑛𝑎)𝐺𝛾𝑏
1 + 𝜔𝐺
where, na = percent air voids
w = water content of compacted soil
d = dry density corresponding to w
G = specific gravity
w = density of water = 1 gm/cm3.
The line showing the dry density as a function of water content for soil containing no air voids is
called the zero air void line or the 100% saturation line and is given as
𝛾𝑑 =𝐺𝛾𝑤
1 + 𝜔𝐺
Alternatively, a line showing the relation between water content and dry density for a constant degree
of saturation Sr, is established from the given equation
𝛾𝑑 =𝐺𝛾𝑤
1 + 𝜔𝐺/𝑆𝑟
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 22
Standard Proctor Test
The standard proctor test was developed by R. R. Proctor. The test consist of compacting the soil at
various water contents in the mould, in three equal layers, each layer being given 25 blows of the 2.5
kg rammer dropped from a height of 30.5 cm.
Modified Proctor Test
Higher compaction is needed for heavier transportation and military air craft. Modified Proctor test
was developed to give a higher standard of compaction. This test was standardized by the American
Association of State Highway Officials and is known as Modified AASHO Test. In this test the soil is
compacted in the standard proctor mould, but in five layers, each layer being given 25 blows of 4.89
kg rammer dropped through a height of 45 cm. The compactive active energy given to the soil in
this test is 27260 kg-cm per 1000 cm3.
APPLICATION
The optimum moisture content and dry density of soil are two of the major data which are needed in
the design of earthen structures soil is used as a fill material
It is useful to understand the dry density and moisture content relationship of soils.
Cohesive subgrade under pavements should preferably be compacted wet of optimum, so that they
may not exhibit large expansion and swelling pressure on submergence.
PROCEDURE
❖ Calculate the volume of proctor mould from the measured dimensions i.e. from diameter and
height of the mould.
❖ Take the weight of the empty mould without base plate & collar.
❖ Take 2.5 kg of dry soil samples, passing through 4.75 mm sieve and add water about 10% by its
volume with the help of measuring cylinder.
❖ Mix the soil and water thoroughly and divide the mix in to 3 parts. Put one part of soil into the
mould after oiling the mould.
❖ Apply full height 25 blows with the rammer put the other two layers of soil & repeat ramming in a
similar fashion while scratching the previous layer for proper bonding.
❖ Measure the weight of soil & mould after leveling the mould & note it. Find bulk density for the
particular reading. From top, bottom and center of the mould keep sample for water content
determination.
❖ Then by an increment of 2% of water added every time repeat the procedure till the weight of
sample starts decreasing, after reaching the maximum bulk density.
❖ Take 2 reading once there is decrease in weight of mould & soil (i.e. decrease in the bulk density).
OBSERVATION DATA
❖ Diameter of mould =
❖ Height of mould =
❖ Initial amount of water added =
❖ Volume of mould =
❖ Weight of empty mould (Without base plate & Collar) =
❖ Weight of dry soil taken =
❖ Specific Gravity of Soil =
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 23
OBSERVATION TABLE
Moisture content
Added
Weight of
mould+soil
gms
Weight
of soil
Gms
Corresponding
container No.
Bulk
density
b
gm/cc
Avg.
Moisture
content
w%
Dry density
𝑑 =𝑏
1 + 𝑤
% Amount(ml)
Container
No.
Wt. of empty
Container (g)
Wt. of container
+ Wet soil (g)
Wt. of container
+ Dry soil (g)
Water content
(%)
Average
Plastic
Limit
CALCULATION
RESULT
The maximum dry density achieved for the given soil using standard proctor test is_________ gm/cc
at an optimum moisture content ________%.
CONCLUSION
REFERENCE
IS: 2720, Part-7, 1980: Methods of test for soils, Part 7: Determination of water content-dry density
relation using light compaction.
IS: 2720, Part-8, 1983: Methods of test for soils, Part 8: Determination of water content-dry density
relation using heavy compaction.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 24
EXPERIMENT 8
CONSOLIDATION/OEDOMETER TEST
AIM
To determine the compressibility i.e. consolidation characteristics of a soil by one dimensional
consolidation using consolidometer apparatus.
APPARATUS
Fixed ring type consolidometer cell assembly consisting of specimen ring of height not less than 20
mm with a height to diameter ratio of about 3, two porous stones, guide ring, outer ring, pressure pad,
steel ball, rubber gasket, Dial gauge with an accuracy of 0.002 mm, filter papers, Stop watch, Water
reservoir, Flexible rubber tube.
THEORY
Consolidation of soil is the process of compression by gradual reduction of pores under a steady
applied pressure. The main purpose of the consolidation test is to obtain soil data required for
predicting the rate and amount of settlement of structures. The data can also be used to develop void
ratio (e) versus pressure (p) curve generally for cohesive soil.
The void ratio (e) of a soil specimen under any applied pressure (p) may be computed using the
following relationship:
𝑒 = 𝐻 − 𝐻𝑠
𝐻𝑠
Where,
H = Height of soil specimen at the end of each pressure increment (cm)
Hs = equivalent height of solids (cm), which is determined as follows:
𝐻𝑠 = 𝑊𝑠
𝐺 𝛾𝑤 𝐴
Where,
Ws = dry weight of the specimen (g)
G = specific gravity of the solid particles
𝛾𝑤 = unit weight of water (g/cc)
A = cross-sectional area of the soil specimen (cm2)
Preparation of Test Specimen
Undisturbed Soil Specimen
Clean, dry and lubricate the consolidation ring from inside with silicon grease. Then weigh it. Record
it as (W1) g.
Preparation from a block (undisturbed) sample
Sometimes, the soil sample from field is also collected as block mass. In that case, cut a sample disc
with two plain faces parallel to each other having its diameter and thickness each at least 10mm greater
than that of the consolidation ring. Hold the consolidation ring vertically with cutting edge downwards
and place it on the prepared disc of the undisturbed soil sample. Using the ring as a template, trim off
the excess soil around the cutting edge. Gently, press the ring downwards with minimum force
required until the soil protrudes into the ring by about 5 mm above its top. Cut the soil at the level of
the-cutting edge of the cutter of the consolidation ring. Trim the excess soil flush with top and bottom
edges of the ring, using straight edge. Remove the small interfering inclusion if any, during trimming
process and fill the cavity completely with the soil from the cuttings. Avoid the excessive remoulding
of the soil surfaces. Keep a portion from the trimmings/cuttings for determination of initial moisture
content and specific gravity. Weigh the ring with the specimen. Record it as (W2) g.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 25
Preparation from a tube sample
To push the sample directly into the consolidation ring, hold the ring firmly about 5 mm above the
sample tube keeping the cutting face downwards. By means of a hydraulic jack, eject the sample
gently and steadily out of the tube so that it intrudes into the ring. During the process, continue
trimming the specimen carefully from outside the consolidation ring to reduce friction. Finally, trim
and flush the soil sample with the ends of the consolidation ring.
Remoulded Specimen
Prepare the soil sample by compaction method in a compaction mould. The compaction efforts
(number of blows required for each layer) may be determined by trial and error if the test is to be
performed at desired moisture content and density, other than optimum moisture content and
maximum dry density. Place the consolidation ring on a glass plate with the cutting edge upwards.
Press the remoulded soil into the ring by suitable means. Flush the soil specimen with the top end of
the ring and weigh. Alternatively the soil specimen may also be intruded into the consolidation ring as
explained.
Dynamically compacted specimen
Weigh the consolidation ring. Attach extension collar to the ring and place it on the base plate. Prepare
about 300 g wet soil for desired water content and density. Calculate the volume of the ring including
collar thickness (For a 60 mm dia. 30 mm total height (including 20 mm soil sample height), volume =
84.86 cm2) and the required quantity of soil. Place this soil in the ring and compact by 2.6 kg rammer
or by any other suitable tool, to the total thickness including that of collar (30 mm). Detach the
extension collar and trim the excess soil flushing with the ring ends to make the thickness of the
specimen as 20 mm. Weigh the ring with compacted soil.
Statically compacted specimen
Prepare the soil specimen by mixing required quantity of water to about 300 g dry soil. Leave the mix
for about 5-6 hours. Keep a small quantity of this mix for moisture content determination. Place the
ring on the base plate and attach the extension collar to it. Weigh the required quantity of the processed
mix of wet soil to obtain the desired test density when compressed to 84.86 cm2 volume. Place gently
the soil into the consolidation ring. Compress this apparatus by means of a suitable pressing device.
Detach the extension collar and trim the soil flushing with the edge of the ring.
Figure 8.1: Consolidation apparatus
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 26
Figure 8.2: Section of Floating Ring consolidation cell (All dimensions in mm)
Figure 8.3: Section of Fixed ring consolidation Cell
APPARATUS
❖ Consolidation Ring
❖ Porous Stone
❖ Consolidation cell
❖ Dial Gauge/LVDT
❖ Loading Ram
❖ Set of weights
PROCEDURE
❖ Soak the porous stones in water and place the bottom porous stone on the base of the
consolidation cell. Keep a filter paper over the stone. Attach guide ring to one or both ends of the
consolidation ring containing soil specimen (as required) and place it gently on the porous stone.
Place another filter paper on the top of specimen and keep upper porous stone and loading cap on
it. Adjust a steel ball in the groove of the loading cap to provide uniform loading on the specimen.
❖ Place this whole arrangement properly in position in the loading device. Check and adjust the
loading beam and the counter balancing system. Level the loading beam with the help of a spirit
level. Clamp the dial gauges in position for recording the compression/swelling of the soil
specimen. Read the initial dial reading and place a 0.05 kg/cm2 seating pressure on the pan of
weight hanger. Connect the base plate of the consolidation cell to water reservoir by means of
rubber/plastic tubing for saturating the soil specimen. Allow the saturation of the specimen for 24
hrs. or more to attain an almost constant dial gauge reading.
❖ Select appropriate sequence of pressures to be applied. It is customary that the pressure applied at
any loading stage is twice that of the proceeding stage pressure. The test, therefore, may be carried
out for loading sequence, to apply pressure on the soil specimen in the range of 0.125, 0.25, 0.5,
1.0, 2.0, 4.0, 8.0 and 16.0 kg/cm2. However some other combination of loads may also be taken as
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 27
per Table 8.1. The maximum pressure to be applied should be more than the effective vertical
pressure envisaged due to in-situ over burden and the proposed structure to be constructed on that
soil.
❖ Take the dial gauge readings after application of each load according to a time sequence (i.e. total
elapsed) such as 0.25, 1.00, 2.25, 4, 6.25, 9, 12.25, 16, 20.25, 25, 36, 49, 64, 100, 144, 196, 225,
256 minutes and thereafter 24 hours. A period of 24 hours is generally sufficient for completion of
primary consolidation of the soil specimen for a particular load. A longer time may be required in
case of hard soil. i.e. soil containing clay particles 25% or (N) SPT values = 30 or qu i.e.
unconfined compressive strength> 4.0 kg/cm2). With the help of the above time sequence it is easy
to plot the specimen thickness against square root of time or logarithm of time. If the object of the
study is to obtain pressure-void ratio relationship only, the time versus dial gauge readings may be
avoided and record only the final dial gauge reading for each load increment after 24 hours.
❖ After completing the dial gauge observations at maximum pressure, release the applied pressure to
zero (0.05 kg/cm'' seating pressure) and leave the soil specimen to swell by water for 24 hours.
Record the final reading of the dial gauge. If required, the loads may be reduced in stages and
time-swelling readings may also be taken accordingly.
❖ Remove the seating load (0.05 kg/cm') and dismantle the consolidation ring. Wipe off water from
the ring and remove filter papers from both the ends of the specimen. Weigh the ring and record it
as (W') g with the specimen and then place it in a container and dry in an oven (105°- 110°C).
Alternatively push the soil specimen out of the ring carefully so that no soil particle is lost, weigh
the specimen and dry. After drying, weigh the ring with the specimen and record it as (W3)g.
Determine the specific gravity of the soil from the dried specimen. Place the porous stones in a
container filled with water and boil for about 20-30 minutes and then clean to remove any soil
particle therein for their further use.
OBSERVATION DATA
Details of Soil Sample
Measurements of container ring:
Diameter (interior) of container =
Area of container =
Initial thickness of soil sample =
Specific gravity of soils =
Equivalent height of solid, Hs =
Least count of Dial gauge =
Wet density =
Dry density =
Moisture Content
Weight of container ring, W1 (g) =
Weight of container ring + Wet soil: W2 (g) =
Weight of container ring + Dry soil: W3 (g) =
Weight of dry soil: Ws (g) =
Weight of water (g) =
Moisture content (%) =
Degree of saturation: S = wG/e =
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 28
OBSERVATION TABLE
Pressure: p (kg/cm2)
Elapsed
time: t
(min) √𝑡 Displacement (mm)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 29
CALCULATION
Applied
pressure: p
(kg/cm2)
Final
displacement
(mm)
Change in
displacement
(mm)
Thickness of
soil sample
(H)
Equivalent
ht. of voids
( H – Hs)
Void ratio
e = H − Hs
Hs
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part-15, 1986: Methods of Test for Soils, Part 15: Determination of Consolidation Properties.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 30
EXPERIMENT 9
DIRECT BOX SHEAR TEST
AIM
To determine shear strength parameters of the given soil sample at known density by conducting direct
shear test.
APPARATUS
Shear box (size 60 mm × 60 mm × 50 mm), Container for shear box, Grid plates, Base plate, Porous
stones, Loading pad, Loading frame, Proving ring with dial gauge/Load cell, Static/dynamic
compaction device, Dial gauge/LVDT, Sample trimmer
THEORY
Shear strength of a soil is its maximum resistance to shearing stresses. It is equal to the shear stress at
failure on the failure plane. Shear strength is composed of: (i) internal frictions, which are the
resistance due to the friction between the individual particles at their contact points and inter locking of
particles. (ii) Cohesion which is the resistance due to inter-particle forces, which tend to hold the
particles together in a soil mass. Coulomb has represented the shear strength of the soils by the
equation:
𝜏𝑓 = 𝑐 + 𝜎 𝑡𝑎𝑛𝜑
Where,
𝜏𝑓 = shear strength of the soil (shear stress at failure)
C = cohesion
𝜎 = normal stress on the failure plane
Ø = angle of internal friction
The parameters C and Ø are not constant for a type of soil but it depends on its degree of saturation
and the condition of the laboratory testing. In direct shear test, initially a normal stress is applied on the
soil specimen. Under the normal stress the pore water pressure gets dissipated leading to the
consolidation of the soil under the normal stress is known as consolidation stage. After the application
of normal stress, shear stress is applied. During the application of shear stress there will be
development of a pore pressure or suction pressure (in very stiff clays and in very dense sands suction
pressures develop during shear). If the shear stress is applied at a very slow rate the developed pore
pressure gets dissipated. This process of applying shear stress is known as stage of shearing.
Depending on whether the dissipation of pore pressure is allowed or not during the application of
consolidation and shear load, the shear tests are classified as follows.
(a) Undrained test: In this, water is not allowed to drain out during the entire test (i.e. during
consolidation and shearing), hence there is no dissipation of pore pressures.
(b) Consolidated undrained test: In this, the soil is allowed to consolidate under the initially applied
normal stress only, hence drainage is permitted under normal stress. But no drainage is allowed during
shear.
c) Drained test: In this, the drainage is allowed throughout the test during the application of both
normal and shear stresses. No pore water pressure is setup at any stage of the test.
Shear parameters are used in the design of earthen dams and embankments. The stability of the failure
wedges depends on the shear resistance of the soil along the failure plane. These strength parameters C
and Ø are used in calculating the bearing capacity of soil-foundation systems. The bearing capacities
of foundations are estimated using Terzaghi's bearing capacity equation or any other bearing capacity
equation. For example the ultimate net bearing capacity of a strip footing is given by the following
equation:
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 31
qu = CNc + (Nq-l) 𝛾Df + 0.5 𝛾B𝑁𝛾
Where,
qu = ultimate bearing capacity of foundation
Df = depth of foundation
B = width of footing
𝛾 = unit weight of soil
Nc, Nq & 𝑁𝛾 = bearing capacity factors (functions of ∅ )
PROCEDURE
❖ Prepare a soil specimen of size 60 mm x 60 mm x 20 mm, either from an undisturbed soil sample
or from a remoulded sample. Soil specimen may also be directly prepared in the box by
compaction.
❖ Obtain the density of soil specimen.
❖ Fix the upper portion of the box to the lower part by fixing pins. Attach the base plate to the lower
part.
❖ Place the porous stone in the box.
❖ For undrained test, place the grid over the porous stone keeping the serrations of the grid at right
angle to the direction of the shear. For consolidated undrained and drained tests use the perforated
grid in place of plane grid.
❖ Transfer the soil specimen prepared in step 1, in the box.
❖ Place the upper grid, porous stone and loading pad in the order on the soil specimen.
❖ Place the box inside the container and mount it on the loading frame.
❖ Bring the upper half of the box in contact with the proving ring assembly. A slight movement of
proving ring dial gauge observes contact.
❖ Fill the container with water if the soil is to be saturated.
❖ Mount the loading yoke on the ball placed on the loading pad.
❖ Put the weights say the loading yoke to apply the normal stress intensity of 0.5 kg/cm2-.
❖ For consolidated undrained and drained tests allow the soil to consolidate fully under this normal
load. This step is avoided, for undrained test.
❖ Remove the fixing pin from the box and raise slightly the upper half of the box with the help of the
spacing screw. Remove the spacing screws also.
❖ Adjust the proving ring dial gauge to zero.
❖ Arrange the shear displacement dial gauge and take its initial reading.
❖ Shear load is applied at a constant rate of strain (for undrained test, the rate of strain is 1 to 15
mm/minute in clay and 1.5 mm-2.5 mm/minute in sand. For drained tests, the rate of strains 0.005-
0.02 mm/minute in clays and 0.2-1.0 mm/minute in sands).
❖ Observe the shear displacement and corresponding proving ring dial gauge readings. Record the
observations.
❖ The reading will increase till the soil fails. Record the proving ring dial gauge reading till the
residual stress is reached after failure. (The failure is assumed, when the proving ring dial gauge
begins to recede after reaching a maximum or at a shear displacement of approximately 20% of the
specimen length.)
❖ Plot the graph between the shear stress and shear strain.
❖ Repeat the test on identical specimen under increasing normal stress 1, 1.5 and 2 kg/cm2.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 32
Figure 9.1: Shear stress-strain curve
Figure 9.2: Failure envelope
OBSERVATION DATA
Dry density of sand =
Area of specimen: 𝐴0 =
Thickness of sample =
Volume of specimen =
Rate of strain =
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 33
OBSERVATION TABLE
Normal stress = 0.50 (kg/cm2)
Sr.
No.
Shearing
displacement:
𝛿 (cm)
Corrected area:
𝐴𝑐 = 𝐴0 (1 − 𝛿
3)
Shear force
(kg)
Shear stress
(kg/cm2)
Normal stress = 1 (kg/cm2)
Sr.
No.
Shearing
displacement:
𝛿 (cm)
Corrected area:
𝐴𝑐 = 𝐴0 (1 − 𝛿
3)
Shear force
(kg)
Shear stress
(kg/cm2)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 34
Normal stress = 1.50 (kg/cm2)
Sr.
No.
Shearing
displacement:
𝛿 (cm)
Corrected area:
𝐴𝑐 = 𝐴0 (1 − 𝛿
3)
Shear force
(kg)
Shear stress
(kg/cm2)
Sr.
No.
Normal stress
(kg/cm2)
Shear force
(kg)
Maximum displacement
(cm) Corrected area Shear stress (kg/cm2)
CALCULATION
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 35
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part-13, 1986: Methods of test for soils, Part 13: Direct shear test.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 36
EXPERIMENT 10
UNCONFINED COMPRESSION TEST
AIM
To determine the unconfined compressive strength and undrained cohesion of the clayey soil.
APPARATUS
Loading frame, Proving ring/Load cell, A dial gauge/LVDT
THEORY
The unconfined compressive strength is defined as the ratio of axial failure load to cross sectional area
of the soil sample when it is not subjected to any lateral pressure.
qu = P/Ac
Where,
qu = unconfined compressive strength
P = axial load at failure
Ac = corrected area at failure = Aa / (l - ∈)
Aa = initial cross sectional area
∈ = axial strain in the sample ∆L/L0
∆L = change in length of the sample
L0 = initial length of the sample
This test is considered as undrained, as the rate of loading does not allow dissipation of pore water
pressure.
Cohesion of the soil sample may be calculated by using the following relations:
σ1 = σ3tan2α + 2c tanα
Where,
𝜎1 = major principal stress at failure
𝜎3= minor principal stress at failure
α = failure angle with the major principal plane = (45° + Ø/2)
Ø = angle of internal friction of the soil
In unconfined compression test, 𝜎3 = 0, 𝜎1 = 𝑞
Hence, σ1 = 2c tan (45° + Ø/2)
If the soil is pure cohesive soil, Ø = 0, therefore,
𝐶 = qu / 2
This is the simplest and quickest test for determining the cohesion and the shear strength of the
cohesive soils. These values are used for checking the short-term stability of foundations and slopes,
soil consistency can be known from the value of unconfined compressive strength.
Table 5.1: Variation of consistency of soil with qu
qu (kg/cm2) Soil consistency
<0.25 Very soft
0.25-0.50 Soft
0.50-1.00 Medium
1.00-2.00 Stiff
2.00-4.00 Very stiff
>4.00 Hard
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 37
PROCEDURE
❖ Prepare the soil sample as explained.
❖ Arrange the sample between the moving base and the top plate connected to the proving ring.
❖ Rise the platform up, so that the soil sample is subjected to compressive force.
❖ Take the dial gauge reading and proving ring readings and record.
❖ The dial gauge reading provides the deformation in the sample and in-turn the strain.
❖ The proving ring reading provides the corresponding load in turn the axial stress on the sample.
❖ Plot graph between axial stress and axial strain. Obtain the peak stress from the graph. This stress
is the unconfined compressive strength of the soil.
Figure 10.1: Unconfined compression test apparatus
Figure 10.2: Axial stress strain graph from unconfined compression test
OBSERVATION DATA
❖ Bulk density of sample: 𝜌𝑏 (𝑔/𝑐𝑐) =
❖ Bulk density of sample: 𝜌𝑑 (𝑔/𝑐𝑐) =
❖ Moisture content: w (%) =
❖ Initial length of Sample: Lo (cm) =
❖ Initial diameter of sample: d (cm) =
❖ Initial cross section of the sample: Ao (cm2) =
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 38
OBSERVATION TABLE
Deformation
(∆L) mm
Strain ∈ =
∆L
L0
Corrected area
Ac = A0
(1−∈)⁄
Load
(kg)
Stress:
σ = PAc
⁄
CALCULATION
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part-10, 1973: Methods of test for soils, Part 10: Determination of unconfined compressive
strength.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 39
EXPERIMENT 11
TRIAXIAL COMPRESSION TESTS
AIM
To determine shear strength parameters of the given soil sample by conducting triaxial shear test.
APPARATUS
Triaxial testing machine complete with triaxial cell, Water pressure unit with hand pump, Proving
ring/Load cell, Dial gauge/LVDT, Dial gauge, Rubber membranes, Membrane stretcher, Sample
trimming apparatus, Bins for moisture content determinations, Balance and box of weights, Drying
oven
THEORY
Triaxial testing is another test used to measure the shear parameters of a given soil. The test is
performed on a cylindrical soil/rock samples. This test is considered to be the most conveniently
available test which accommodates a good number of drainage conditions to suit the field situations.
PROCEDURE
❖ Trim the soil specimen (prepared from the sampling tube of, an undisturbed sample tube using
universal extractor frame. or from a compacted soil specimen as per standard proctor method, at
optimum moisture content or any other moisture content to suite the field situations).Using the
trimming apparatus if necessary the trimmed specimen should be 76 mm long and 38 mm in
diameter. The diameter and the length are measured at not less than 3 places and the average values
are used for computations. Note the weight of the specimen (W1).
❖ The specimen is then enclosed in a 38 mm diameter and about 100mm long rubber membrane,
using the membrane stretcher. Spreading back the ends of the membrane over the ends of the
stretcher and applying suction between the stretcher and the rubber membranes does this by
inhalation . The membrane and the stretcher are then easily slide over the specimen, the suction is
released and the membrane is unrolled from the ends of the stretcher.
❖ Use non-porous stones on either side of the specimen as neither any pressure is to be measured nor
any drainage of air or water is allowed.
❖ Remove the porous cylinder from its base removing the bottom fly nuts. The pedestal at the centre
of the base of the cylinder on which the specimen is to be placed is cleaned and a 38 mm diameter
rubber O-ring is rolled over to its bottom. The specimen along with the non-porous plate on either
side is centrally placed over the pedestal and the bottom edge of the machine covering the
specimen is sealed against the pedestal by rolling back the O-ring over the membrane.
❖ The cap is placed over the top plate of the specimen and the top of the rubber membrane is sealed
against the cap by carefully rolling over it another O-ring. This arrangement of rubber O-ring
forms the effective seal between the specimen with the membrane and the water under, pressure.
The specimen is checked for its verticality and co-axially with the cylinder chamber.
❖ The chamber (cylinder) along with the loading plunger is carefully placed over its base without
disturbing the soil specimen and taking care to see that the plunger rests on the cap of the specimen
centrally. The loading frame is then adjusted so that it just touches the plunger top by naked eye.
The chamber is then rotated if necessary such that the dial gauge recording compression rests
centrally over the top of the screw which can be locked at any level and which is attached to the
top of the cylinder chamber carrying the specimen. The cylinder is then attached to the base plate
tightly by means of tightening the nuts.
❖ The valve to drain out the chamber and the valve to drain out the air and water from the sample are
closed and the air lock nut at the top of the cylinder is kept open to facilitate the exit of air as water
enters the chamber through another valve which connects the chamber to the water storage cylinder
subjected to a pressure by a hand pump.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 40
❖ The water storage cylinder is filled with water completely and its top is then closed by means of a
valve. Necessary pressure is built up in the cylinder by working the hand pump and the pressure
communicated to the cylinder where the specimen is placed, by opening the connecting valve. The
cylindrical chamber is allowed to be filled up completely which is indicated by the emergence of
water through the airlock nut at the top of the chamber. Then the airlock nut is closed to develop
necessary confining pressure by using the hand pump and the same is maintained constant.
❖ If necessary, bring the loading plunger down until it is in contact with the specimen top cap by
means of hand operated loading device. This is indicated by a spurt in the reading of the proving
ring dial gauge.
❖ For this position, adjust the deformation dial gauge reading to zero.
❖ Record the initial readings of the proving ring and compression dial gauge.
❖ The vertical load is applied to the specimen by starting the motor at the loading frame. The change
in the proving ring dial gauge gives the measure of the applied load. The deformation dial gauge
gives the deformation in the soil specimen, which can be used to compute strain in the soil.
❖ Take the readings of proving ring dial gauge at 0.5, 1.0, 1.5, 2.0% (or any other smaller values) of
strain and for every 1.0% strain thereafter up to failure or 20% strain whichever is earlier.
❖ Throughout the test, make sure that the chamber, containing pressure is kept constant at the
desirable value as indicated by the pressure gauge on the water cylinder. If necessary, the pressure
can be made good for any possible losses by working the hand pump.
❖ After the specimen has failed or 20% strain is recorded, as the case may be (a) stop application of
load (b) disconnect the chamber from water storage cylinder by closing the linger valve (c) open
the airlock knob a little and (d) open the valve to drain out the water in the cylinder. After a few
seconds open the airlock nut completely to facilitate quick draining out of water, by entry of air at
top of the cylinder.
❖ After the water is completely drained out, take out the cylinder from loading frame carefully,
loosen the nuts and remove the Lucite cylinder from its base, without disturbing the sample.
❖ Note the space of the failed specimen, angle of shear plane if any and dimensions of the specimen.
❖ Wipe of the rubber membrane dry and find its weight W2 that should be same as W1.
❖ Remove the membrane from the specimen and take a representative specimen preferably from the
sheared zone.
❖ Repeat the test with three samples of the same specimen subjected to three different lateral
pressures (confining) of 0.5, 1.0 and 1.5 kg/cm2 (5, 10 and 15psi. or 50, 100 and 150 kpa).
OBSERVATION TABLE
❖ Diameter of the sample =
❖ Density of sample =
❖ Height of the sample =
Trial 1: Confining pressure 𝜎3 =
Sr.
No.
Axial Deformation
(mm)
Strain
(%)
Axial Load: P
(kN)
Deviator stress: (𝜎1 − 𝜎3) =
P/A (kN/m2)
Major principal
stress: 𝜎1
(kN/m2)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 41
Trial 2: Confining pressure 𝜎3 =
Sr.
No.
Axial Deformation
(mm)
Strain
(%)
Axial Load: P
(kN)
Deviator stress: (𝜎1 − 𝜎3) =
P/A (kN/m2)
Major principal
stress: 𝜎1
(kN/m2)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 42
Trial 3: Confining pressure 𝜎3 =
Sr.
No.
Axial Deformation
(mm)
Strain
(%)
Axial Load: P
(kN)
Deviator stress: (𝜎1 − 𝜎3) =
P/A (kN/m2)
Major principal
stress: 𝜎1
(kN/m2)
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 43
CALCULATION
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part-11, 1971: Methods of test for soils, Part 11: Determination of the shear strength
parameters of a specimen tested in unconsolidated undrained triaxial compression without the
measurement of pore water pressure.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 44
EXPERIMENT 12
LABORATORY VANE SHEAR TEST
AIM
To determine the undrained shear strength, of a given cohesive soil using laboratory vane shear
apparatus.
APPARATUS Laboratory vane shear apparatus, Marble plate or glass plate, Spatula, Balance, thermostatically controlled hot
air oven, Containers for moisture content determination, Wash bottle containing distilled water, 0.425 mm IS
sieve.
THEORY This test is performed to find shear strength of a given (generally very soft) soil specimen. Vane shear test is a
useful method of measuring the shear strength of soft clay. It is a cheaper and quicker method. The test can be
conducted in field as well as in laboratory. The laboratory vane shear test for the measurement of shear strength
of cohesive soils is useful for soils of low shear strength (less than 0.3 kg/cm2) for which unconfined tests
cannot be performed.
Where, S = Undrained shear strength of soil in (kg/cm2);
T = Torque in cm-kg (corrected for the vane rod and torque rod resistance, if any);
D = Diameter of vane (in cm);
H = Height of vane (in cm)
APPLICATION
The test gives the undrained strength of the soil. The undisturbed and remolded strength obtained are
also useful for evaluating the sensitivity of soil. The data acquired from vane shear test can be used to
determine:
❖ Undrained shear strength
❖ Evaluate rapid loading strength for total stress analysis
❖ Sensitivity of soil to disturbance
❖ Analysis of stability problems with embankment on soft ground
PROCEDURE
❖ In case of remolded soil specimen, the dry weight of soil and the required water content to be taken
depends on the requirement. (Usually in-situ dry density and water content will be taken for sample
preparation). ❖ Prepare eight specimens of the soil sample by rapidly mixing the soil with the water taken until
uniform soil sample is obtained. The uniformly prepared sample is filled in the specimen container
whose height is 76mm and diameter is 38mm (Having (H/D) aspect ratio of 2). ❖ The application of torque can be done using springs of different stiffness referred as spring
constants (2, 4, 6, 8 kg-cm). To start with, the spring of stiffness (spring constant, 2 kg-cm) is
attached to the vane shear apparatus. ❖ Mount the specimen container with the specimen on the base of the vane shear apparatus. If the
specimen container is closed at one end, it should be provided with a hole of about 1 mm diameter
at the bottom.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 45
❖ Gently lower the shear vanes into the specimen to their full length without disturbing the soil
specimen. The top of the vanes should be at least 10 mm below the top of the specimen. Note the
initial readings of the (upper and lower) needles of angle of twist before applying torque.
❖ Both needles should essentially be at the same angle before starting the experiment.
❖ Rotate the vanes at a uniform rate (say 0.1º per second) by suitably operating the torque application
handle until the lower needle of angle handle reverts back which signifies the failure of soft soil
specimen.
❖ Note the final reading of the angle of twist by measuring the upper needle’s indicated angle.
❖ Find the value of blade height in cm and find the value of blade diameter (total width) in cm.
❖ The same procedure needs to be done by changing the springs of other stiffness/spring constant say
4, 6, 8 kg-cm.
❖ The repetition of tests for all springs of different stiffness is mandatory for reporting the results.
OBSERVATION DATA ❖ Diameter of the vane: D (cm) =
❖ Height of the vane : H (cm) =
❖ Spring constant: k (kg-cm) =
OBSERVATION TABLE
Sr.
No.
Initial
reding
(Deg.)
Final
reading
(Deg.)
Difference
(Deg.)
T = (Spring
constant*Difference)/180
S
(kg/cm2)
Avg. S
(kg/cm2)
CALCULATION
RESULT
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 46
CONCLUSION
REFERENCE
IS: 2720, Part 30: Methods of test for soils, Part 30: Laboratory vane shear test.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 47
EXPERIMENT 13
STANDARD PENETRATION TEST
AIM
To obtain the penetration resistance (N-value) and collect disturbed soil sample.
APPARATUS
Tripod (to give a clear height of about 4 m; one of the legs of the tripod should have ladder to facilitate
a person to reach tripod head), Tripod head with hook, Pulley, Guide pipe assembly (with a 75 cm
clear travel for the standard 65 kg weight and provision to connect to A-drill extension rods), Standard
split spoon sampler, A-dril rods (heavy duty) for extending the test to deeper depths; number of rods
depends on the depth of exploration, Heavy duty Post hole auger (100 mm or 150 mm diameter),
Heavy duty helical auger, Heavy duty auger extension rods, Rope, Measuring tape
THEORY
The standard penetration test (SPT) is a standardized method of sounding (IS: 2131). The test is
performed at the site in a clean bore-hole of 55 mm to 150 mm diameter. A casing or drilling mud is
used to support the sides of the bore hole if required.
In this test, a thick wall standard split spoon sampler, 50.8 mm outer diameter and 35 mm inner
diameter, is driven into the undisturbed soil at the bottom of the bore hole under the blows of a 65 kg
drive weight with 75 cm free fall. The minimum open length of the sampler should be 60 cm. The
number of blows required to drive the sampler 30 cm beyond the seating drive of 15 cm, is termed as
the penetration resistance N. There are a number of empirical relationships available between N-values
and relative density, unit weight, angle of internal friction, bearing capacity of soils as shown in Tables
2.1 and 2.2.
From Tables 2.1 and 2.2 it can be observed that by obtaining the N-value at a location, the soil
properties can be approximately assessed. Knowing the angle of internal friction 𝜑, of gravelly soils
the bearing capacity factors Nq and Nγ can be read from standard Tables or charts and the bearing
capacity of foundation can be estimated.
SPT values obtained in the field for sand have to be corrected before they are used in empirical
correlations and design charts. IS: 2131-1981 recommends that the field value of N be corrected for
two effects, namely, (a) effect of overburden pressure, and (b) effect of dilatancy.
(a) Correction for overburden pressure
Several investigators have found that the overburden pressure influences the penetration resistance of
the N value in a granular soil. If two granular soils possessing the same relative density but having
different confining pressures are tested, the one with a higher confining pressure gives a higher N
value. Since the confining pressure (which is directly proportional to the overburden pressure)
increases with depth, the N values at shallow depths are underestimated and the N values at larger
depths are overestimated. Hence, if no correction is applied to recorded N values, the relative densities
at shallow depths will be underestimated and at higher depths, they will be overestimated. To account
for this, N values recorded from field tests at different effective overburden pressures are corrected to a
standard effective overburden pressure.
The corrected N value is given by
𝑁′ = 𝐶𝑁 𝑁
Where,
𝑁′ = corrected value of observed N value
𝐶𝑁 = correction factor for overburden pressure
𝑁 = recorded or observed N value in the field
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 48
IS: 2131-1981 suggested the following chart for the overburden pressure correction (Figure 13.1). The
equation for the chart is written as:
𝐶𝑁 = 0.77 log10
20
𝑃0
Figure 13.1: Correction factor 𝐶𝑁 due to overburden
(b) Correction for dilatancy
Dilatancy correction is to be applied when N′obtained after overburden correction, exceeds 15 in
saturated fine sands and silts. IS: 2131-1981 incorporates the Terzaghi and Peck recommended
dilatancy correction (when 𝑁′ > 15) using the equation
𝑁′′ = 15 + 0.5 (𝑁′ − 15)
Where;
𝑁′′ = final corrected value to be used in design charts
𝑁′ > is an indication of dense sand.
In such a soil, when dynamic loads are applied in saturated state the pore pressure will not be in a
position to get dissipated due to low permeability. Hence, during dynamic loading (i.e. application of
blows) the pore water will offer a temporary resistance to dynamic loads. This leads to higher N value
which is unsafe. Therefore when SPT is performed in saturated silt and fine sands and if the observed
N value is more than 15, a correction has to be applied to reduce the observed value.
CN
Effe
ctiv
e o
verb
urd
en p
ress
ure
(P
0)
kg/c
m2
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 49
Table 13.1: Empirical values of γ, Dr and φ of cohesion less soils based on the corrected N-value
N-Value Nature of soil Relative
density,
Dr
(%)
Unit
weight, ϒ
(kN/m3)
Approximate angle of
internal friction,∅°
5-6 Very loose-
Loose
15 11-18
27 - 32°
8-15 Loose-Medium 35 14 – 20 30 - 35°
10-40 Medium-Dense 65 17 – 22 35 - 40°
20-70 Dense-Very
dense
85 17 – 23
38 - 43°
>35 Very dense 100 20 – 23 -
Table 13.2: Empirical values of unconfined compressive strength of clay soils based on N-value
N - Value Nature
of soil
Unconfined compressive
strength: qu (kPa)
2 Very soft - Soft 25
4 Soft - Medium 50
8 Medium - Stiff 100
16 Stiff – Very Stiff 200
32 Very Stiff - Hard 400
APPLICATION
❖ Finding relative density of coarse grain soil
❖ Finding friction angle of coarse grain soil
❖ Finding bearing capacity of coarse grain soil
❖ Finding settlement of coarse grain soil
PROCEDURE
❖ The borehole is advanced to the required depth and the bottom cleaned.
❖ The split-spoon sampler, attached to standard drill rods of required length is lowered into the
borehole and rested at the bottom.
❖ The split-spoon sampler is driven into the soil for a distance of 450 mm by blows of a drop hammer
(monkey) of 65 kg falling vertically and freely from a height of 750 mm. The number of blows
required to penetrate every 150 mm is recorded while driving the sampler. The number of blows
required for the last 300 mm of penetration is added together and recorded as the N value at that
particular depth of the borehole. The number of blows required to effect the first 150 mm of
penetration, called the seating drive, is disregarded.
❖ The split-spoon sampler is then withdrawn and is detached from the drill rods. The split-barrel is
disconnected from the cutting shoe and the coupling. The soil sample collected inside the split
barrel is carefully collected so as to preserve the natural moisture content and transported to the
laboratory for tests. Sometimes, a thin liner is inserted within the split-barrel so that at the end of the
SPT, the liner containing the soil sample is sealed with molten wax at both its ends before it is taken
away to the laboratory.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 50
Figure 13.2: Line sketch of SPT Set-up
Figure 13.3: Typical representation of SPT results in a bore log
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 51
OBSERVATION DTA
❖ Bulk unit weight: γ (kN/m3) =
❖ Saturated unit weight =
❖ Submerged unit weight: γ’ (kN/m3) =
❖ Water table depth =
OBSERVATION TABLE
Sr.
No.
Dept
of
testing
(m)
Description
of strata
Observed
N-value
Overburden
pressure:
P0 (kg/cm2) N’ N’’
Corrected
N-value Remark
CALCULATION
RESULT
CONCLUSION
REFERENCE
IS: 2131-1981(Reaffirmed 2002): Method for standard penetration test for soils.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 52
EXPERIMENT 14
CALIFORNIA BEARING RATIO (CBR) TEST
AIM
To determine the California bearing ratio by conducting a load penetration test in the laboratory.
APPRATUS
Cylindrical mould with inside dia 150 mm and height 175 mm, provided with a detachable extension
collar 50 mm height and a detachable perforated base plate 10 mm thick, Spacer disc 148 mm in dia
and 47.7 mm in height along with handle, Weight 2.6 kg with a drop of 310 mm (or) weight 4.89 kg a
drop 450 mm, One annular metal weight and several slotted weights weighing 2.5 kg each, 147 mm in
dia, with a central hole 53 mm in diameter, ith a capacity of atleast 5000 kg and equipped with a
movable head or base that travels at an uniform rate of 1.25 mm/min. Complete with load indicating
device, Metal penetration piston 50 mm dia and minimum of 100 mm in length, Two dial gauges
reading to 0.01 mm, 4.75 mm and 20 mm I.S. Sieves, Miscellaneous apparatus, such as a mixing bowl,
straight edge, scales soaking tank or pan, drying oven, filter paper and containers.
THEORY
CBR is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at
the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material.
C.B.R. = (Test load/Standard load) * 100
The following table gives the standard loads adopted for different penetrations for the standard
material with a C.B.R. value of 100%
Penetration of plunger
(mm)
Standard load
(kg)
2.5 1370
5.0 2055
7.5 2630
10.0 3180
12.5 3600
The test may be performed on undisturbed specimens and on re-moulded specimens which may be
compacted either statically or dynamically.
Interpretation and recording
C.B.R. of specimen at 2.5 mm penetration
C.B.R. of specimen at 5.0 mm penetration
C.B.R. of specimen at 2.5 mm penetration
The C.B.R. values are usually calculated for penetration of 2.5 mm and 5 mm. Generally the C.B.R.
value at 2.5 mm will be greater that at 5 mm and in such a case/the former shall be taken as C.B.R. for
design purpose. If C.B.R. for 5 mm exceeds that for 2.5 mm, the test should be repeated. If identical
results follow, the C.B.R. corresponding to 5 mm penetration should be taken for design.
If the initial portion of the curve is concave upwards, apply correction by drawing a tangent to the
curve at the point of greatest slope and shift the origin (Figure 14.1). Find and record the correct load
reading corresponding to each penetration.
C.B.R. = (PT/PS) * 100
where PT = Corrected test load corresponding to the chosen penetration from the load penetration
curve.
PS = Standard load for the same penetration taken from the table.
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 53
Figure 14.1: Load vs penetration curve
APPLICATION
❖ Design of highway pavement thickness.
❖ Design of Airfield pavement thickness.
PROCEDURE
Attach the cutting edge to the mould and push it gently into the ground. Remove the soil from the
outside of the mould which is pushed in . When the mould is full of soil, remove it from weighing the
soil with the mould or by any field method near the spot.
Determination of the density
Remoulded specimen
Prepare the remoulded specimen at Proctors maximum dry density or any other density at which
C.B.R> is required. Maintain the specimen at optimum moisture content or the field moisture as
required. The material used should pass 20 mm I.S. sieve but it should be retained on 4.75 mm I.S.
sieve. Prepare the specimen either by dynamic compaction or by static compaction.
Dynamic Compaction
Take about 4.5 to 5.5 kg of soil and mix thoroughly with the required water.
Fix the extension collar and the base plate to the mould. Insert the spacer disc over the base Place the
filter paper on the top of the spacer disc.
Compact the mix soil in the mould using either light compaction or heavy compaction. For light
compaction, compact the soil in 3 equal layers, each layer being given 55 blows by the 2.6 kg rammer.
For heavy compaction compact the soil in 5 layers, 56 blows to each layer by the 4.89 kg rammer.
Remove the collar and trim off soil.
Turn the mould upside down and remove the base plate and the displacer disc.
Weigh the mould with compacted soil and determine the bulk density and dry density.
Put filter paper on the top of the compacted soil (collar side) and clamp the perforated base plate on to
it.
Static compaction
Calculate the weight of the wet soil at the required water content to give the desired density when
occupying the standard specimen volume in the mould from the expression.
W =desired dry density * (1+w) V
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 54
Where W = Weight of the wet soil
w = desired water content
V = volume of the specimen in the mould = 2250 cm3 (as per the mould available in laboratory)
Take the weight W (calculated as above) of the mix soil and place it in the mould.
Place a filter paper and the displacer disc on the top of soil.
Keep the mould assembly in static loading frame and compact by pressing the displacer disc till the
level of disc reaches the top of the mould.
Keep the load for some time and then release the load. Remove the displacer disc.
The test may be conducted for both soaked as well as unsoaked conditions.
If the sample is to be soaked, in both cases of compaction, put a filter paper on the top of the soil and
place the adjustable stem and perforated plate on the top of filter paper.
Put annular weights to produce a surcharge equal to weight of base material and pavement expected in
actual construction. Each 2.5 kg weight is equivalent to 7 cm construction. A minimum of two weights
should be put.
Immerse the mould assembly and weights in a tank of water and soak it for 96 hours. Remove the
mould from tank.
Note the consolidation of the specimen.
For Penetration
Place the mould assembly with the surcharge weights on the penetration test machine. (Fig.39).
Seat the penetration piston at the center of the specimen with the smallest possible load, but in no case
in excess of 4 kg so that full contact of the piston on the sample is established.
Set the stress and strain dial gauge to read zero. Apply the load on the piston so that the penetration
rate is about 1.25 mm/min.
Record the load readings at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10 and 12.5 mm.
Note the maximum load and corresponding penetration if it occurs for a penetration less than 12.5 mm.
Detach the mould from the loading equipment. Take about 20 to 50 g of soil from the top 3 cm layer
and determine the moisture content.
OBSERVATION DATA
For Dynamic Compaction
❖ Optimum water content (%) =
❖ Weight of mould + compacted specimen (g) =
❖ Weight of empty mould (g) =
❖ Weight of compacted specimen (g) =
❖ Volume of specimen (cm3) =
❖ Bulk density (g/cc) =
❖ Dry density (g/cc) =
For static compaction
❖ Dry density (g/cc) =
❖ Moulding water content (%) =
❖ Wet weight of the compacted soil: W (g) =
For penetration Test
❖ Calibration factor of the proving ring:
❖ Surcharge weight used (kg) =
❖ Water content after penetration test (%) =
❖ Least count of penetration dial:
GEOTECHNICAL ENGINEERING (3130606) LAB MANUAL 55
OBSERVATION TABLE
Penetration
(mm)
Proving ring Dial
gauge reading
(division)
Load on
plunger
(kg)
Corrected
load
(kg)
Standard
load
(kg)
from table
CBR(%)
determine by
equation
CALCULATION
RESULT
CONCLUSION
REFERENCE
IS: 2720, Part 16: Methods of test for soils, Part 16: Laboratory determination of CBR.