Direct Shear Test

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Definition - What does Direct Shear Test mean?

The direct shear test is a procedure conducted on soil samples to determine its shear strength, which is the maximum resistance that the soil can withstand when subjected to shearing.

The direct shear test is commonly performed, is simple to conduct, and can be performed on undisturbed or remolded samples. For remolding, a soil sample can be compacted at optimum moisture content in a compaction mold. The strength of a soil depends on its resistance to shearing stresses.

ASTM D3080-04 describes the standard test method for the direct shear test of soils under consolidated drained conditions.

Trenchlesspedia explains Direct Shear Test

The direct shear test is performed by deforming a soil specimen at a controlled strain rate on or near a single shear plane. The soil specimen is placed in a shear box with a loading area for the normal load to be applied. The shear box restricts the soil specimen's horizontal strain but allows shearing on the horizontal plane.

The normal load is applied on the soil specimen and it is sheared across a predetermined horizontal plane between the two halves of the shear box apparatus. Three or more specimens are tested under different normal loads to determine their effects on shear resistance and displacement.

The measurements for normal displacement, shear load, and shear displacement are recorded. The shear strength is evaluated using the Mohr-Coulomb Failure Criterion, which assumes that the shear strength depends on the normal effective stress, friction angle of the material, and cohesion of the material.

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