Numerical analysis on mechanical difference of sandstone under in-situ stress, pore pressure preserved environment at depth

Deep in-situ rock mechanics considers the influence of the insitu environment on mechanical properties, differentiating it from traditional rock mechanics. To investigate the effect of in-situ stress, pore pressure preserved environment on the mechanical difference of sandstone, four tests are numerically modeled by COMSOL: conventional triaxial test, conventional pore pressure test, in-situ stress restoration and reconstruction test, and insitu pore pressure-preserved test (not yet realized in the laboratory). The in-situ stress restoration parameter is introduced to characterize the recovery effect of in-situ stress on elastic modulus and heterogeneous distribution of sandstone at different depths. A random function and non-uniform pore pressure coefficient are employed to describe the non-uniform distribution of pore pressure in the in-situ environment. Numerical results are compared with existing experimental data to validate the models and calibrate the numerical parameters. By extracting mechanical parameters from numerical cores, the stress-strain curves of the four tests under different depths, in-situ stress and pore pressure are compared. The influence of non-uniform pore pressure coefficient and depth on the peak strength of sandstone is analyzed. The results show a strong linear relationship between the in-situ stress restoration parameter and depth, effectively characterizing the enhanced effect of stress restoration and reconstruc-tion methods on the elastic modulus of conventional cores at different depths. The in-situ pore pressure-preserved test exhibits lower peak stress and peak strain compared to the other three tests, and sand-stone subjected to non-uniform pore pressure is more prone to plastic damage and failure. Moreover, the influence of non-uniform pore pressure on peak strength gradually diminished with increasing depth.(c) 2023 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).