Direct Shear Test

Direct Shear Test

In the design and construction of bridges, foundation, retaining walls, skyscrapers, etc, the value of the angle of internal friction and cohesion of the soil involved are required for the design. The angle of internal friction and cohesion of the soil can be determined by the Direct shear test. The laboratory test of Direct shear test procedures for determining these values for cohesionless soils. 

APPARATUS :-

• Direct shear box apparatus
• Loading frame (motor attached).
• Dial gauge.
• Proving ring.
• Tamper.
• Straight edge.
• Balance to weigh upto 200 mg.
• Aluminium container.
• Spatula.

KNOWLEDGE OF EQUIPMENTS :-

The direct shear testing machine consists of shear box, soil container, loading unit, proving ring, dial gauge to measure shear deformation and volume changes. The direct share box can be splitted into two piece square shear box.  The shear load is  indicated by a proving ring which may be taken by the soil initiated in the shearing plane.

PROCEDURE :-

1. Check and clean the shear box, shear mould. Measure the inner dimension and volume of the shear mould. 
2. Assemble the soil container.
3. Fill the soil in soil container in three layer by gently compacted.
4. Weight the container and determined the volume. Distinguish the two weight and find out the density of the soil sample.
5. Place the soil container to the shear box, and place the shear box to the Direct shear test instrument.
6. Install the proving ring to determined the applied shear load. Set the dial gauge of the proving ring to zero.
7. Install a couple of dial gauge for determine the normal load and the horizontal deflection. Set the both dial gauge to zero.
8. Provide a normal load to the soil container by the arrangement of head weight. 
9. To create a shear plain, remove the pin from the shear container of shear box.
10. Start the motor, and take the appropriate reading of horizontal dial gauge corresponding to the proving ring.
11. Add the normal stress of 0.5 kg/cm² , and take corresponding readings, and noted down. 

OBSERVATION :-

Normal stress 0.5 kg/cm^{2    ;} L.C=.......    P.R.C=.........

Normal stress 1.0 kg/cm²   L.C=.......    P.R.C=........

Normal stress 1.5 kg/cm²   L.C=.......    P.R.C=........

Important in Direct shear test-

Plot a graph Normal stress vs. Shear stress, And a graph of Deflection vs. Shear stress.

PRECAUTIONS :-

• Carefully clean the shear box and soil specimen in Direct shear test.
• Carefully note down the weight and dimensions.
• Take the readings of dial gauge by perpendicular view of eye and the dial gauge.