Measurement and Analysis of Pore Pressure Effects in the Inelastic Deformation of Rocks.

摘要

Cyclic experimental tests on water-saturated rock samples exhibit effects which are unexplainable in terms of the usual constitutive models for rock. A formal theory of plasticity based on the law of effective stress and the associated flow rule is developed in detail and applied to the specific cases of a linear Mohr-Coulomb failure envelope and a cap of the type used to describe the behavior of McCormic Ranch sand. It is found that both models have serious disadvantages when applied to fluid-saturated rocks under conditions of nonzero pore pressure. Experimental techniques are described for measurement of pore pressure under undrained test conditions. Results of undrained laboratory tests are presented in which pore pressure is measured as a function of the externally applied mean stress, deviatoric stress and volumetric strain in sandstone samples saturated to levels of 80%, 85%, 90% and 95%.