Test: Direct Shear - Civil Engineering (CE) MCQ

Shearing resistance can be determined in the laboratory by following four methods
i) Direct shear test
ii) Tri axial shear test
iii) Unconfined shear test
iv) Vane shear test.

Depending upon drainage conditions, three types of shear tests have been developed:
a) Un-drained test or quick test
b) Consolidated un-drained test
c) Drained test.

Since the shearing strain is made to increase at a constant rate in a direct shear test, and hence the test is called the Strain controlled shear box test.

Shear-box test is most commonly used apparatus for direct shear test.

To conduct un-drained test, plane grids are used and for the drained test, perforated grids are used.

 In drained test, perforated grids are sheared sufficiently slowly so that complete dissipation of pore pressure takes place.

The stress condition across the soil sample is very complex. The distribution of normal stresses and shearing stresses over the potential surface of sliding is not uniform. The entire strength of the soil is not mobilized simultaneously.

 As the soil in drained test is sheared sufficiently slowly so that complete dissipation of pore pressure takes place, it takes 2 to 5 days long for shearing cohesive type of soil.

As compared to the tri axial system, there is a little control on the drainage of soil in direct shear test.

 In direct shear test, the stress condition across the soil sample are very complex, the stress is more at the edges and less in the Centre. Due to this there is a progressive failure of the specimen.