Strength Behavior, Creep Failure and Permeability Change of a Tight Marble Under Triaxial Compression

The coupled hydro-mechanical behaviors of a tight marble are investigated by a series of laboratory tests with continuous gas injection during the hydrostatic compression, triaxial compression and compressive creep tests. Hydrostatic compression tests are firstly carried out in three steps to identify the viscous effect of hydrostatic stress on deformation and permeability of the marble. Coupled triaxial tests are then conducted at a constant axial strain rate under five different confining pressures (P _c) with continuous gas injection. Coupled creep behaviors of the marble are also characterized by a constant deviatoric stress test under P _c = 30 MPa with gas flowing at a constant injection pressure. The high-stress unloading failure behavior of the marble is finally investigated by an unloading test with a previous multi-step creep phase to realize a high-stress state as well as to investigate the time-dependent deformation of marble under different deviatoric stresses. Experimental results reveal that gas permeability of the marble shows an evident rate-dependent effect in hydrostatic compression. Mechanical behaviors of the tight marble are closely depended on the applied P _c in triaxial tests, and its permeability exhibits a decrease phase at initial deviatoric loading and turns to increase at a critical stress corresponding to the initial yield stress. Marble can withstand more important plastic deformation under high P _c than under lower ones. Gas flow seems to be more sensitive than the strains to characterize the creep behaviors of the marble. No time-dependent strains are observed when deviatoric creep stress is lower than 50% of its peak strength under P _c = 30 MPa.