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Direct Shear

Test Method

ASTM Designation: D 3080, “Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions”

Summary of Test Method

This test method covers the determination of the consolidated drained shear strength of a soil material in direct shear. The test is performed by deforming a specimen at a controlled strain rate on or near a single shear plane determined by the configuration of the apparatus. Generally, three or more specimens are tested, each under a different normal load, to determine the effects upon shear resistance and displacement, and strength properties such as Mohr strength envelopes. This test method consists of placing the test specimen in the direct shear device, applying a predetermined normal stress, providing for wetting and/or draining of the test specimen, consolidating the specimen under the normal stress, unlocking the frames that hold the test specimen, and displacing one frame horizontally with respect to the other at a constant rate of shearing deformation and measuring the shearing force and horizontal displacements as the specimen is sheared.

The direct shear test is suited to the relatively rapid determination of consolidated drained strength properties because the drainage paths through the test specimen are short, thereby allowing excess pore pressure to be dissipated more rapidly than with other drained stress tests. The test can be made on all soil materials and undisturbed, remolded or compacted materials. There is however, a limitation on maximum particle size.

The test results are applicable to assessing strength in a field situation where complete consolidation has occurred under the existing normal stresses. Failure is reached slowly under drained conditions so that excess pore pressures are dissipated. The results from several tests may be used to express the relationship between consolidation stress and drained shear strength.

Minimum Sample Size

Undisturbed Sample: 1 Tube (1 lb)
Remolded Sample: 2 Canvas Bags (80 lb)

Last Updated September 29, 2005

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