Investigating the coupling effects of temperature levels and heating-water cooling cycles on the physical and mechanical responses of HDR (hot dry rock) is a vital issue during the exploitation of geothermal energy. In this study, the physical properties of granite specimens were measured first after each heating and water-cooling cycle. Then, uniaxial compressive tests were conducted on those granites to obtain their mechanical properties. With the increase in heating temperature (T) and cycles of heating and water cooling (N), P-wave velocity, uniaxial compression strength (UCS), and elastic modulus (E) showed a decreasing tendency, and the decrease of those four properties corresponding to T variation is greater than N variation. Due to the α-β phase transition of quartz happening at 573°C, the density UCS and E of granite decreased rapidly when the heating temperature increased from 450°C to 600°C at N = 1. With the increase of T and N, the failure mode of granite gradually changes from tensile failure to shear failure and, finally, comminute failure. The failure mechanism of granite gradually transfers from brittleness-dominated to ductility-dominated due to accumulated thermal damage. Finally, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to determine the damage mechanism of cyclic heating-cooling. The micro test results show that the high-temperature treatment changes the mineral composition and the microcracks number of the granite and finally affects the macroscopic physical and mechanical properties. The study conclusions of this manuscript are important for exploiting geothermal resources.

True triaxial compression experiments were conducted on jointed rock with different Joint Roughness Coefficient (JRC, JRC = 4.78, 9.57, 14.74 and 19.47) or inclined angle (α = 30°, 45°, 60° and 90°) firstly. Then, the adaptive transform a Lagrangian solid element to Discrete Element Sphere particles (adaptive Solid to DES) method was employed to realize the true triaxial compression simulation on jointed rock with various JRC and α. The results show that: (1) The maximum equivalent stress and cracks are firstly concentrated at the joint asperities and develop into the rock matrix with increasing axial stress, resulting in joint-matrix coupled fracture mode. (2) The strength and peak strain of the jointed rock show a decreasing (30 ° ≤ α ≤ 60°) then increasing α = 90°) tendency as the α increased. Increasing JRC weaks the influence of α on strength but amplify on peak strain. (3) When the joint strike parallels to intermediate principal stress, the failure mode are matrix shear (α = 30°), matrix shear-joint sliding (α = 45°), joint sliding (α = 60°), to matrix shear failure (α = 90°), respectively. When the joint strike parallels to minor principal stress, the larger stress on the inclined side inhibits the influence of the joint, resulting in all jointed rock matrix shear fracture.