Description

A Triaxial Testing Machine is used to measure the mechanical properties of many deformable solids, especially soil. 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. Once the specimen is inside the triaxial cell, the cell pressure is increased to a predetermined value by rotating the knob, and the specimen is brought to failure by increasing the vertical stress by applying a constant rate of axial strain.

Saturation and consolidation are not permitted to keep the original structure and water content of sample untouched. Pore pressures are not measured during this test and therefore the results can only be interpreted in terms of total stress. These tests are generally carried out on three specimens of the same sample subjectedto different confiningstresses. Since all specimens are supposedly saturated the shear strength are similar for all tests. The results of the test are plotted as curves of principal stres difference against strain.

For conditions of maximum principal stress difference (taken as failure) Mohr circles are plotted in terms of total stress. The average undrained shear strength should be noted, and the failure envelope drawn tangential to the Mohr circles in order to find the “undrained cohesionintercept” and undrained “angle of shearing resistance”.