Consolidated undrained triaxial testing

Pore and back pressures are not measured during this test and therefore the results can only be interpreted in terms of total stress over a confinement pressure stress.

application of triaxial test

During CD cycles - stiff enough to preserve the imprinted pattern. Measuring the pore pressures in the sample sometimes called CUpp allows approximating the consolidated-drained strength.

Consolidated undrained triaxial testing

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. It provides improved measurements of volumetric response - as during isotropic yielding, volumetric strain is distributed isotopically within the specimen. True Triaxial Test[ edit ] Triaxial testing systems have been developed to allow independent control of the stress in three perpendicular directions. Shear speed is often calculated based on the rate of consolidation under a specific confining pressure whilst saturated. It is recommended by several standard test methods that a value of B greater than, or equal to, 0. 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. Samples can even be liquefied to a large strain amplitude, then crushed to CU failure. The sample is compressed at a constant rate strain-controlled.

The wrinkles formed due to extreme volume change imposed by iterating between CU liquefaction and draining. First, three specimens are tested and consolidated at three different effective pressures, in order to give specimens of different strengths which will produce widely spaced effective stress Mohr circles.

Consolidated drained triaxial test

Confining pressures can vary anywhere from 1 psi to psi or greater, sometimes requiring special load cells capable of handling higher pressures. The combination of high automation, improved sample durability and large deformation compatibility expands the scope of triaxial testing. Saturation is normally carried out by leaving the specimens to an elevated back pressure so that the air in the pores is dissolved in water. It provides improved measurements of volumetric response - as during isotropic yielding, volumetric strain is distributed isotopically within the specimen. Unconsolidated Undrained UU [ edit ] In an ' unconsolidated undrained' test the loads are applied quickly, and the sample is not allowed to consolidate during the test. The rate of axial deformation is kept constant, 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. For conditions of maximum principal stress difference taken as failure Mohr circles are plotted in terms of total stress.

Consolidated Drained CD Test: The consolidated drained triaxial compression test, with volume change measurement during shear is carried out in a similar sequence to the consolidated undrained test, but during shear the back pressure remains connected to the specimen which is loaded sufficiently slowly to avoid the development of excess pore pressures.

It is recommended by several standard test methods that a value of B greater than, or equal to, 0.

triaxial test apparatus description

Post-liquefaction testing. During isotropic yielding volumetric strain is isotopically distributed within the specimen, this improves measurement of volumetric response during CD tests and pore water pressure during CU loading.

During the shear stage the vertical stress is increased by the loading ram, and measurements are made at regular intervals of deformation, ram load and pore pressure.

Consolidated drained triaxial test example

Samples can even be liquefied to a large strain amplitude, then crushed to CU failure. When the consolidation cell pressure and back pressure are applied to the specimen, readings of volume change are made using a volume change device in the back pressure line. The "new" apparatus has been upgraded to "the Danish triaxial" by L. During the shear stage the vertical stress is increased by the loading ram, and measurements are made at regular intervals of deformation, ram load and pore pressure. No bulging or shear rupture is present despite numerous instances of pure plastic yielding. 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. Control of the apparatus is highly automated, thus cyclic loading can be applied with great efficiency and precision. Saturation is normally carried out by leaving the specimens to an elevated back pressure so that the air in the pores is dissolved in water. Building constructions, excavations, tunnelling and similar applications have several effects on the subsoil structures and these effects are successfully simulated with Triaxial Tests where the stress-strain relation of undisturbed soil specimen are investigated by subjecting the soil sample to different stress levels and drainage conditions. Unconsolidated Undrained UU Test For the UU test , the specimens assumed to be saturated prior to test are subjected to a confining fluid pressure in a triaxial chamber. 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 Danish triaxial can yield CD and CU sand specimens into plasticity without forming a shear rupture or bulging. Saturation is carried out in order to ensure that the pore fluid in the specimen does not contain free air.

Unconsolidated Undrained UU Test For the UU testthe specimens assumed to be saturated prior to test are subjected to a confining fluid pressure in a triaxial chamber.

consolidated undrained triaxial test mohr circle

This allows investigation of stress paths not capable of being generated in axisymmetric triaxial test machines, which can be useful in studies of cemented sands and anisotropic soils.

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Triaxial shear test