Experimental study on mechanical and permeability behaviors of sandstone under real-time temperature

In order to explore the evolution characteristics of mechanical and permeability properties of sandstone under real-time temperature conditions in deep geological environments, thermal-hydraulic-mechanical (THM) coupling tests were conducted on sandstone specimens at temperatures ranging from 25 °C to 95 °C. The tests were performed using the Rock Top multi-field coupling tester to investigate the changes in strength, deformation, and permeability of the sandstone across the specified temperature range. Furthermore, scanning electron microscopy (SEM) was employed to analyze the microstructure of the sandstone and its influence on mechanical properties. The results indicate that with increasing temperature, the strength of sandstone initially increases and then decreases, while the peak strain exhibits a rapid and nonlinear increase. Furthermore, the permeability of sandstone decreases initially and then increases as the temperature rises, demonstrating lower sensitivity to temperature variations compared to confining pressure. At various temperatures, the failure modes observed in sandstone consistently demonstrate typical shear slip characteristics. Moreover, at elevated temperatures, there is a significant increase in the number of cracks observed on the failure surface of sandstone. Under the action of lower temperature (25℃~65℃) the pores and micro-cracks of sandstone appear highly compact, and the new cracks are relatively few, but under the action of higher temperature (75℃~95℃), the size and number of defects in sandstone increase obviously, which is the fundamental factor that leads to the change of mechanical and permeability characteristics of sandstone. The research findings presented in this paper provide theoretical support for assessing the stability of surrounding rock in high geothermal tunnel.