The shear strength of a soil mass is the internal resistance per unit area that the soil . The direct shear test and the triaxial test are the two commonly used. Shear tests are generally carried out oil small soil samples in the laboratory to of shear tests commonly used are the direct shear test and the triaxial test. Triaxial shear test of soils. 1. Triaxial Shear Test By: Amardeep Singh; 2. Strength of different materials Steel Tensile strength Concrete.
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Test Execution[ edit ] For soil samples, the specimen is contained in a cylindrical latex sleeve with a flat, circular metal plate or platen closing off the top and bottom ends. This cylinder is placed into a bath of a hydraulic fluid to provide triaxial shear test of soil along the sides of the cylinder.
The top platen triaxial shear test of soil then be mechanically driven up or down along the axis of the cylinder to squeeze the material. The distance that the upper platen travels is measured as a function of the force required to move it, as the pressure of the surrounding water is carefully controlled.
The net change in volume of the material can also be measured by how much water moves in or out of the surrounding bath, but is typically measured - when the sample is saturated with water - triaxial shear test of soil measuring the amount of water that flows into or out of the sample's pores.
Rock[ edit ] For testing of high-strength rock, the triaxial shear test of soil may be a thin metal sheeting rather than latex. Triaxial testing on strong rock is fairly seldom done because the high forces and pressures required to break a rock sample require costly and cumbersome testing equipment.
Triaxial shear test - Wikipedia
Effective Stress[ edit ] The effective stress on the sample can be measured by using a porous surface on one platen, and measuring the pressure of the fluid usually water during the test, then calculating the effective stress from the total stress and pore pressure.
Triaxial test to determine the shear strength of a discontinuity[ edit ] The triaxial triaxial shear test of soil can be used to determine the shear strength of a discontinuity.
A homogeneous and isotropic sample fails due to shear stresses in the sample. If a sample with a discontinuity is orientated such that the discontinuity is about parallel to the plane in which maximum shear stress will be developed during the test, the sample will fail due to shear displacement along the discontinuity, and hence, the shear strength of triaxial shear test of soil discontinuity can be calculated.
NPTEL :: Civil Engineering - Soil Mechanics
Consolidated Drained CD [ edit ] In a ' consolidated drained' test the sample is consolidated and sheared in compression slowly to allow pore pressures built up triaxial shear test of soil the shearing to dissipate. The rate of axial deformation is kept constant, i. The idea is that the test allows the sample and the pore pressures to fully consolidate i.
The test may take a long time to allow the sample to adjust, in particular low permeability samples need a long time to drain and adjust strain to stress levels. Consolidated Undrained CU [ edit ] In a 'consolidated undrained' test the sample is not allowed to drain.
The shear characteristics are measured under undrained conditions and the sample is assumed to triaxial shear test of soil fully saturated.
Measuring the pore pressures in the sample sometimes called CUpp allows approximating the consolidated-drained strength. Shear speed is often calculated based on the rate of consolidation under a specific confining pressure whilst saturated.
Confining pressures can vary anywhere from 1 psi to psi or triaxial shear test of soil, sometimes requiring special load cells capable of handling higher pressures. Unconsolidated Undrained UU [ edit ] In an ' unconsolidated undrained' triaxial shear test of soil the loads are applied quickly, and the sample is not allowed to consolidate during the test.
The sample is compressed at a constant rate strain-controlled. True Triaxial Test[ edit ] Triaxial testing systems have been developed to allow independent control of the stress in three perpendicular directions.
Triaxial shear test
This allows investigation of stress paths not capable of triaxial shear test of soil generated in axisymmetric triaxial test machines, which can be useful in studies of cemented sands and anisotropic soils. The test cell is cubical, and there are six separate plates applying pressure to the specimen, with LVDTs reading movement of each plate.
The apparatus is significantly more complex than for axisymmetric triaxial shear test of soil tests, and is therefore less commonly used.
Free end condition in triaxial testing[ edit ] The Danish triaxial in action Triaxial tests of classical construction had been criticized for their nonuniform stress and strain field imposed within the specimen during larger deformation amplitudes.
To test specimens during larger deformation amplitude, "new"  triaxial shear test of soil "improved"  version of the triaxial apparatus were made. Both the "new" and the "improved" triaxial follow the same principle - sample height is reduced down to one diameter height and friction with the end plates is canceled.