Experimental investigation on mechanical behavior, energy evolution and gas permeability of anisotropic phyllite subjected to triaxial compression and cyclic loading

Abstract

The bedding plane direction significantly affects the mechanical properties, deformation and gas permeability evolution of rock mass in gas storage engineering. In this paper, for phyllite, a series of triaxial compression with cyclic loading and gas permeability apparatus are conducted to investigate such directional effect. The peak stress, Young’s modulus, energy evolution, failure mode and gas permeability coefficient are analyzed. For triaxial compression test, with increasing inclination angles, the deformation parameters (E, E50, μ) and characteristic stress parameters (σcc, σci, σcd) both show a U-shape pattern. For triaxial cyclic loading test, the peak stress of specimen first decreases and then increases, i.e., the peak stresses at the inclination angles of 0°, 30°, 45°, 60° and 90° are 118.18, 84.35, 64.18, 42.54 and 84.57 MPa, respectively. The energy evolutions of specimens at different inclination angles are similar, but increase with increasing cyclic number. i.e., when β=60°, with the cycle number increasing from 1 to 3, the elastic strain energy, the dissipated strain energy and the total strain energy increase by 343.55%, 175.08%, and 259.87%, respectively. In addition, the failure mode of phyllite specimens is analyzed and summarized as three distinct types, i.e., tensile-shear failure, shear-sliding failure and split-shear failure. The relationships between the initial gas permeability and confining pressure, deviatoric stress show positive correlations. The failure of layered phyllite is most likely to occur at a bedding plane inclination angle of 45° to 60°.