Effects of Piston Uplift, Piston Friction, and Machine Deflection in Reduced Triaxial Extension Testing

A series of Reduced Triaxial Extension (RTE) tests were conducted on dummy (brass) and null (water) samples to determine the effects of (corrections required for) piston uplift, piston friction and system compliance associated with RTE tests. During the consolidation stage of RTE tests, the sample may be consolidated in isotropic or anisotropic stress conditions. During the shearing stage of an RTE test, the sample is unloaded in the axial direction by decreasing the deviator stress while the radial stress remains constant. Ten (10) tests were conducted on a brass "dummy" sample. The device was assembled in the same manner as for tests conducted on soil samples. The tests simulated the backpressure saturation and consolidation stages of testing. For various effective stresses (cell pressure and backpressure combinations) the load associated with piston uplift and piston friction was measured. Correlations were developed for piston uplift and piston friction. Eleven (11) tests were on "dummy" ice samples The samples, used as place holders, were set-up in the same manner as for tests conducted on soil samples then allowed to melt before shearing. For various effective stresses the load associated with machine deflection was measured. The contribution of the membrane elongation and filter paper were determined.