Deformation characteristics, gas permeability and energy evolution of low-permeability sandstone under cyclic loading and unloading path

To guarantee the safety and stability of underground disposal, deformation behavior and permeability evolution of host rock mass are studied in the present work, with a special attention to the influence of loading and unloading cycles of deviatoric stress and confining pressure. A series of triaxial compression tests with loading-unloading cycles and gas permeability measurements are performed on a low-porosity sandstone using a rock automatic servo-controlled triaxial testing system. Young's modulus, Poisson's ratio, Biot's coefficient, gas permeability and energy evolution of studied sandstone obtained under different levels of confining pressure and deviatoric stress are analyzed and discussed. Under cyclic loading and unloading, Poisson's ratio of sandstone increases linearly with increasing of cycle number while elastic modulus of specimens increases firstly, and then tends to a constant value and terminates by a decrease phase. Moreover, with the increase of cycle number, the permeability decreases firstly and then increases progressively, even a rapid increase after peak stress. These phenomena are related to the propagation and compaction of micro-cracks inside the sandstone specimens.

Automated summary

This study investigates the deformation behavior and permeability evolution of the host rock mass in underground disposal, with a focus on the influence of loading and unloading cycles. The results demonstrate that cyclic loading and unloading can induce the propagation and compaction of micro-cracks in the sandstone specimens, which in turn affect the mechanical properties and permeability of the rock.