Direct shear test

The direct shear test is performed to determine the shear strength parameters for a given type of soil. A normal load is applied to the soil specimen and the soil is sheared across the pre-determined horizontal plane between the two halves of the shear box. During shearing, the shear load, shear displacement, and normal displacement are recorded. The test finalizes as soon as the shear stress remains stable or starts decreasing. This is an indication that the soil cannot withstand the extra load since the specimen has probably broken down.

The test is repeated for two or more identical specimens under different normal loads. From the results, we can determine the shear strength parameters.

The shear strength is expressed as S= c+ σ tanφ

Where c = effective cohesion, σ= effective stress, φ= effective angle of shearing resistance.