The Behavior of Induced Pore Fluid Pressure In Undrained Triaxial Shear Tests On Fractured Porous Analog Rock Material Specimens
Six series of triaxial tests were performed on intact and fractured porous rock analog material specimens for various confining and pore pressures and drainage (drained and undrained) conditions. It was found that physico-mechanical properties are affected by water and Terzaghi′s effective stress law holds for this analog material. Under undrained test conditions, pore water pressure increases as the specimens volume is reduced, and vice versa. The maximum induced pore pressure is a function of the confining pressure, initial pore pressure and volumetric strain. Similarly to the intact material, the fractured samples showed that the behavior of pore pressure is closely related to the volume change. The application of a deviatoric stress initially produced an increasing phase of pore pressure during the friction mobilization phase. After the friction mobilization phase, the roughness is mobilized and this corresponds to the beginning of a progressive decrease of pore pressure. The increase and decrease in pore pressure is different from one sample to the other mainly due to the influence exerted by the roughness morphology different for each fracture.