Tri-axial compression test in cohesion-less soil (Demonstration Only)

 AIM: 

To determine the undrained shear strength of the cohesive soil using vane shear.

THEORY: 

The strength test more commonly used in a research laboratory today is the triaxial

compression test, first introduced in the U.S.A. by A. Casagrande and Karl Terzaghi in

1936 – 37. The soil specimen, cylindrical in shape, is subjected to direct stresses acting

in three mututally perpendicular directions. In the common solid cylindrical specimen

test, the major principal stress σ1 is applied in the vertical direction, and the other two

principal stresses σ2 and σ3 σ2 σ3) are applied in the horizontal direction by the fluid

pressure round the specimen 

APPARATUS REQUIRED:

KNOWLEDGE OF EQUIPMENT

1) A constant rate of strain compression machine of which the following is a brief 

description of one is in common use.

a) A loading frame in which the load is applied by a yoke acting through an elastic 

dynamometer, more commonly called a proving ring which used to measure the load.

The frame is operated at a constant rate by a geared screw jack. It is preferable for the

machine to be motor driven, by a small electric motor. 

b) A hydraulic pressure apparatus including an air compressor and water reservoir in

which air under pressure acting on the water raises it to the required pressure, together

with the necessary control valves and pressure dials. 

2) A triaxial cell to take 3.8 cm dia and 7.6 cm long samples, in which the sample can

be subjected to an all round hydrostatic pressure, together with a vertical compression

load acting through a piston. The vertical load from the piston acts on a pressure cap.

The cell is usually designed with a nonferrous metal top and base connected by tension

rods and with walls formed of perspex. 

Apparatus for preparation of the sample:

1) 3.8 cm (1.5 inch) internal diameter 12.5 cm (5 inches) long sample tubes.

2) Rubber ring.

3) An open ended cylindrical section former, 3.8 cm inside dia, fitted with a small 

rubber tube in its side.

4) Stop clock. 

Direct shear test in cohesion-less soil

 AIM:

To determine the shearing strength of the soil using the direct shear apparatus. 

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 is 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 soil by the equation : 

APPARATUS REQUIRED:

1) Direct shear box apparatus

2) Loading frame (motor attached).

3) Dial gauge.

4) Proving ring. 

5) Tamper.

6) Straight edge.

7) Balance to weigh upto 200 mg.

8) Aluminum container.

9) Spatula. 

PROCEDURE:

• Check the inner dimension of the soil container. 

• Put the parts of the soil container together.

• Calculate the volume of the container. Weigh the container.

• Place the soil in smooth layers (approximately 10 mm thick). If a dense sample is 

desired tamp the soil.

• Weigh the soil container, the difference of these two is the weight of the soil. 

Calculate the density of the soil.

• Make the surface of the soil plane.

• Put the upper grating on stone and loading block on top of soil.

• Measure the thickness of soil specimen. 

• Apply the desired normal load. 

Determination of Liquid Limit and Plastic Limit

 AIM 

To determine the liquid limit and plastic limit of the given soil sample

THEORY AND APPLICATION 

Liquid limit is significant to know the stress history and general properties of the soil

met with construction. From the results of liquid limit the compression index may be

estimated. The compression index value will help us in settlement analysis. If the

natural moisture content of soil is closer to liquid limit, the soil can be considered as

soft if the moisture content is lesser than liquids limit, the soil can be considered as

soft if the moisture content is lesser than liquid limit. The soil is brittle and stiffer. The

liquid limit is the moisture content at which the groove, formed by a standard tool into

the sample of soil taken in the standard cup, closes for 10 mm on being given 25

blows in a standard manner. At this limit the soil possess low shear strength. 

The moisture content expressed in percentage at which the soil has the smallest

plasticity is called the plastic limit. Just after plastic limit the soil displays the

properties of a semi solid. For determination purposes the plastic limit it is defined as

the water content at which a soil just begins to crumble when rolled into a thread of

3mm in diameter. The values of liquid limit and plastic limit are directly used for

classifying the fine grained soils. Once the soil is classified it helps in understanding

the behaviour of soils and selecting the suitable method of design construction and

maintenance of the structures made-up or and resting on soils. 

APPARATUS REQUIRED: 

1) Measuring balance 

2) Liquid limit device (Casagrandes) 

3) Grooving tool 

4) 425 micron sieve 

5) Glass plate 

6) Spatula 

Determination of Grain Size Distribution (Hydrometer Analysis)

 AIM 

To determine the grain size distribution of soil sample containing appreciable amount

of fines by hydrometer analysis test. 

THEORY 

For determining the grain size distribution of soil sample, usually mechanical analysis 

(sieve analysis) is carried out in which the finer sieve used is 63 micron or the nearer

opening. If a soil contains appreciable quantities of fine fractions in (less than 63

micron) wet analysis is done. One form of the analysis is hydrometer analysis. It is

very much helpful to classify the soil as per ISI classification. The properties of the soil

are very much influenced by the amount of clay and other fractions. 

APPARATUS REQUIRED 

1. Hydrometer

2. Glass measuring cylinder-Two of 1000 ml capacity with ground glass or rubber 

stoppers about 7 cm diameter and 33 cm high marked at 1000 ml volume.

Thermometer- To cover the range 0 to 50º C with an accuracy of 0.5 º C. 

3. Water bath.

4. Stirring apparatus.

5. I.S sieves apparatus.

6. Balance-accurate to 0.01 gm.

7. Oven-105º to 110º.

8. Stop watch.

9. Desiccators

10. Centimeter scale.

11. Porcelain evaporating dish.

12. Wide mouth conical flask or conical beaker of 1000 ml capacity.

13. Thick funnel-about 10 cm in diameter.

14. Filter flask-to take the funnel.

15. Measuring cylinder-100 ml capacity.

16. Wash bottle-containing distilled water. 

Determination of Grain Size Distribution (Sieve Analysis)

 AIM

To conduct sieve analysis of soil to classify the given coarse grained soil. 

THEORY 

Grain size analysis is used in the engineering classification of soils. Particularly coarse 

grained soils. Part of suitability criteria of soils for road, airfield, levee, dam and other

embankment construction is based on the grain size analysis. Information obtained

from the grain size analysis can be used to predict soil water movement. Soils are

broadly classified as coarse grained soils and fine grained soils. Further classification

of coarse grained soils depends mainly on grain size distribution and the fine grained

soils are further classified based on their plasticity properties. The grain size

distribution of coarse grained soil is studied by conducting sieve analysis. 

APPARATUS REQUIRED

1.  A set of Sieves 4.75 mm, 2.36 mm ,1.18 mm ,0.60mm, 0.425 mm, 0.30 

mm 0.15 mm 0.075mm including lid and pan

2. Tray

3. Weighing Balance

4. Sieve Shaker

5. Brush 

PROCEDURE

1. Weigh 500gms of soil sample, of which grain size distribution has to be studied.

2. Clean the sieve set so that no soil particles were struck in them.

3. Arrange the sieves in order such that coarse sieve is kept at the top and the 

fine sieve is at the bottom. Place the closed pan below the finest sieve.

4. Take the soil obtained into the top sieve and keep the lid to close the top sieve.

5. Position the sieve set in the sieve shaker and sieve the sample for a period of 

10 minutes.

6. Separate the sieves and weigh carefully the amount of soil retained on each 

sieve, This is usually done by transferring the soil retained on each sieve on a

separate sieve of paper and weighing the soil with the paper. 

7. Enter the observations in the Table and calculate the cumulative percentage of

soil retained on each sieve. 

To determine the specific gravity of soil solids

 AIM 

To determine the specific gravity of soil solids.

THEORY  

 

Specific gravity of soil solids is the ratio of weight, in air of a given volume; of dry soil

solids to the weight of equal volume of water at 4ºC.Specific gravity of soil grains gives

the property of the formation of soil mass and is independent of particle size. Specific

gravity of soil grains is used in calculating void ratio, porosity and degree of saturation,

by knowing moisture content and density. The value of specific gravity helps in

identifying and classifying the soil type. 

APPARATUS REQUIRED

1. Pycnometer

2. 450 mm sieve

3. Weighing balance

4. Oven

5. Glass rod

6. Distilled water 

PROCEDURE

1. Dry the pycnometer and weigh it with its cap. (W1)

2. Take about 200gmof oven dried soil passing through 4.75mm sieve into the 

pycnometer and weigh again (W2).

3. Add sufficient de-aired water to cover the soil and screw on the cap.

4. Shake the pycnometer well and remove entrapped air if any.

5. After the air has been removed, fill the pycnometer with water completely.

6. Thoroughly dry the pycnometer from out side and weigh it (W3).

7. Clean the pycnometer by washing thoroughly.

8. Fill the cleaned pycnometer completely with water up to its top with cap screw on.

9. Weigh the pycnometer after drying it on the outside thoroughly (W4). 

10.Repeat the procedure for three samples and obtain the average value of specific gravity.

 

RESULT

 

Average specific gravity of soil solids G =