Correct option is A
Direct Shear Test:
This test also called the shear box test, is the oldest shear test that is in use and also quite simple to perform.
The soil specimen that is to be tested, is confined in a metal box of a square cross-section that is split into two halves horizontally, and a small clearance is maintained between the two halves of the box. if the specimen is fully or partially saturated, perforated metal plates and porous stones are placed above and below the specimen to allow free drainage. A solid metal plate is used if the specimen is dry.
A vertical load is applied to the specimen through a static weight hanger and the soil is sheared gradually by applying a horizontal force which causes the two halves of the box to move relative to each other. The shear is normally applied at a constant rate of strain. The magnitude of the shear load is measured by means of a proving ring.
The shear deformation as well as the vertical deformation (change in thickness) are measured during the test with the help of dial gauges.
This test is best suitable for free drainage soil like sand and gravel.
The failure plane is predetermined.
