Evolution of mechanical parameters of deep sandstone and its constitutive model under the condition of different stress paths

Abstract

Using a multifunctional true triaxial fluid–solid coupling system, the mechanical properties of deep sandstone and its constitutive model were studied under the simulated depths 1000, 1500, and 2000 m and different stress paths. In stress path 1, σz is increased while unloading along the x-axis (σx decreased). Path 2 involves an increase in σz with two-sided unloading. Path 3 involves an increase in σz with one-sided unloading σx and σy true triaxial loading. In addition, the evolution law of the Poisson’s ratio μ and deformation modulus E of the deep sandstone under different stress paths and simulated depths were studied. The experimental results show that the following: (1) The μ–σz curves of the sandstone at different simulated depths and the same stress path are similar. As σz increases, the Poisson’s ratio first decreases and then increases to a maximum value, and subsequently, it abruptly decreases. On the other hand, the initial value of the deformation modulus E increases with an increase in the simulated depth. (2) Under the same simulated depth and different stress paths, the deformation trends of the E–σz curves of the deep sandstone are quite different. Under the stress paths 1 and 2, the deformation modulus E of the deep sandstone first increases and then sharply decreases as σz increases. On the other hand, it first decreases and then increases under the condition of stress path 3. (3) A constitutive model for the deep sandstone is proposed herein. The research results can provide some important references for deep rock mechanics.