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.