Government Engineering College, Dahod Applied Mechanics

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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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


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

(%)


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.


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.


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)


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.


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.


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


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.


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.


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.


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


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.


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


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.


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


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


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) =


❖ 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


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.


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


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 =


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.


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.


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


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


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 =


OBSERVATION TABLE

Pressure: p (kg/cm2)

Elapsed

time: t

(min) √𝑡 Displacement (mm)


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.


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:


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.


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 =


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)


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


RESULT

CONCLUSION

REFERENCE

IS: 2720, Part-13, 1986: Methods of test for soils, Part 13: Direct shear test.


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


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) =


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.


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.


❖ 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)



Sr.

No.

Axial Deformation

(mm)

Strain

(%)

Axial Load: P

(kN)


P/A (kN/m2)

Major principal

stress: 𝜎1

(kN/m2)



Sr.

No.

Axial Deformation

(mm)

Strain

(%)

Axial Load: P

(kN)


P/A (kN/m2)

Major principal

stress: 𝜎1

(kN/m2)


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.


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.


❖ 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


CONCLUSION

REFERENCE

IS: 2720, Part 30: Methods of test for soils, Part 30: Laboratory vane shear test.


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


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


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.


Figure 13.2: Line sketch of SPT Set-up

Figure 13.3: Typical representation of SPT results in a bore log


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.


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



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.


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


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:


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.

Documents

Government Engineering College, Dahod Applied Mechanics