Characterization of the creep behavior and modeling considering viscoelastic-plastic damage of quartz sandstone under thermo-hydro-mechanical conditions

Deep underground civil works such as surrounding rocks of oil, gas pipelines and geothermal wellbore that pass through groundwater are often affected by the combined influences of thermal, hydraulic, and mechanical factors. In order to investigate the long-term stability of rock masses of this environment, creep experimental of quartz sandstone under the coupling effect of thermo-hydro-mechanical conditions. The study involved analyzing the long-term creep deformation, isochronous stress-strain curves, and long-term strength variations. Additionally, a fractional-order viscoelastic-plastic creep damage model was developed by integrating statistical damage analysis, Biot's coefficient, and fractional-order integration theory. This model aimed to characterize the three-stage creep properties of different temperatures and water pressures. The experimental results indicate that the creep strain of quartz sandstone gradually increases with temperature and pore water pressure, while the long-term strength decreases. The axial creep strains of quartz sandstone are 0.330% at 20 degrees C, 0.381% at 50 degrees C, 0.448% at 70 degrees C, and 0.473% at 90 degrees C, respectively. This observation suggests that the coupled effect of temperature and pore water pressure has caused a certain level of damage to the rock. Furthermore, the proposed creep model effectively captured characteristics subjected to coupling effects of thermo-hydro-mechanical factors. The results provide a relevant reference value for the theoretical study of the creep mechanical behavior of rocks in multi-field environments.