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A direct shear test is a laboratory or field test used by geotechnical engineers to measure the shear strength properties of soil [1] [2] or rock [2] material, or of discontinuities in soil or rock masses. [2] [3] The U.S. and U.K. standards defining how the test should be performed are ASTM D 3080, AASHTO T236 and BS 1377-7:1990, respectively.
Direct shear test ASTM D3080. The direct shear test determines the consolidated, drained strength properties of a sample. A constant strain rate is applied to a single shear plane under a normal load, and the load response is measured. If this test is performed with different normal loads, the common shear strength parameters can be determined ...
Triaxial apparatus with sample attached ready for testing. In materials science, a triaxial shear test is a common method to measure the mechanical properties of many deformable solids, especially soil (e.g., sand, clay) and rock, and other granular materials or powders.
The shear strength of soil depends on the effective stress, the drainage conditions, the density of the particles, the rate of strain, and the direction of the strain. For undrained, constant volume shearing, the Tresca theory may be used to predict the shear strength, but for drained conditions, the Mohr–Coulomb theory may be used.
On the other hand, when a granular material starts in a very loose state it may continuously compact instead of dilating under shear. A sample of a material is called dilative if its volume increases with increasing shear and contractive if the volume decreases with increasing shear. [7] [8] Dilatancy is a common feature of soils and sands. Its ...
Laboratory tests are more accurate than tests with do-it-yourself kits and electrical meters. An example soil sample report is provided for reference by Wallace Laboratories LLC. In order to avoid complex and expensive analytical techniques, prediction based on regression equations relating to more easily measurable parameters can be provided ...
One common tool advanced during CPT testing is a geophone set to gather seismic shear wave and compression wave velocities. This data helps determine the shear modulus and Poisson's ratio at intervals through the soil column for soil liquefaction analysis and low-strain soil strength analysis. Engineers use the shear wave velocity and shear ...
The shear vane consists of a straight rod with four vanes on one end, arranged in a cruciform pattern, and a combined handle/torque gauge. The rod is inserted into the soil to a depth of 500mm and rotated at a rate of between 6 and 12 degrees per minute. Once the soil fails in shear the gauge shows the maximum torque applied.