Study On The Mechanical Property Of A Sandstone Under Geothermal-mechanical And Hydraulic-mechanical Coupling

The west route of south-to-north water transfer project is situated in the north-east of Qingzhang plateau, which aims at accounting for the lackage of water in north China by transferring water from the upper of Yangtze River to the upper of Yellow River via the mountain of Bayangela. In the engineering deep tunnels will be excavated to transfer water. According to the plan, the tunnels will pass through the region existing high geotemperature, high ground water and high geostress. The study of coupling behavior of three fields (high geothermal field, high hydraulic field and high geostress field) is very important for the excavating, bolting design and stability analyzing for tunnels. In the thesis, the mechanical behaviors of the sandstone from the project have been studied through a series of coupled triaxial tests of confining pressures (from 0 to 60MPa ) and temperatures (room temperature to 70℃) as well as confining pressures (from 25 to 60MPa ) and pore pressure (from 0 to 10MPa ), and an empirical constitutive law concerning geotemperature has been researched.The results of the study show that the strength of the rock sample increases clearly with the increasing confining pressure at the same pore pressure, and decreases with the increasing pore pressure under the same confining pressure. The main reason of the influence is the clear decreasing of cohesion of the sandstone, although the friction angle doesn't change clearly comparing to the cohesion, but it has the same tendency as the cohesion. It is also shown that the Young's modulus of dry rock is affected slightly by the confining pressure. Nevertheless, it is revealed that under the lower pore pressure, the Young's modulus of rock samples increases with the increasing confining pressures, but under higher pore pressure, it decreases with the increasing pore pressures. The failure state of the sandstone under pore pressure exhibits brittle-tensile feature.The relation between the strength of the sandstone and temperature is complex.The strength of the rock is higher under the higher confining pressure regardless the temperature, while the influence of temperature reveals difference: the strength increases with the temperature when the confining pressure is lower than 40MPa; however, when the confining pressure is higher than 40MPa, the strength tends to decrease with increasing temperature. It also exhibits that the cohesion increased greatly with the temperature. Moreover, it reveals that the Young'modulus doesn't change distinctly with confining pressures, but it is higher than that in room temperature when temperature increases. The ductile feature increase with confining pressure, but it is complex under temperature.Moreover, an empirical constitutive law considering geotemperature is proposed, which parameters are related to temperature.