Experimental study on hydraulic and mechanical properties of fault rock under the thermal-hydraulic-mechanical coupling

The exploitation of hydrothermal geothermal resources (HGR) in fault zone is one of the most promising technical schemes for geothermal energy development. To understand the hydraulic and mechanical behaviors of rock mass in fault zone, a series of thermal-hydraulic-mechanical (THM) coupling tests of fault rocks were conducted, and the influence of the fault gouge content, water temperature, seepage pressure and stress on the permeability, porosity, secant Young's modulus, cohesion and internal friction angle of fault rocks was investigated. The results show the permeability evolution can be divided into four stages: slight decline stage, slight rise stage, steady increase stage and rapid increase stage. The porosity evolution can be classified into two stages: seepage dominant stage and axial compression dominant stage, and the time-varying law of porosity of cemented rock mass are significantly different. With the increase of content of fault gouge, the secant Young's modulus, cohesion and internal friction angle of fault rocks gradually increase; while the temperature has little significance on the three parameters. With the increase of seepage pressure, the secant Young's modulus, cohesion and internal friction angle decrease; while the three parameters increase accordingly with the increase of the axial and confining pressure. The research results enrich the study of THM coupling properties of fault rocks, and provide a theoretical basis for exploiting HGR by fault.