Damage and failure mechanism of concentric perforated granite under static pressure after alternating action of high temperature and water at different temperatures

Abstract

In this study, concentric perforated granite alternately treated with high temperature and water at different temperatures was evaluated based on the engineering environment of surrounding rock in the deep geothermal well energy storage area. The damage and failure mechanism of concentric perforated granite under radial load was studied using a combination of mechanical test, theoretical analysis, and numerical simulation. The results revealed that the inner bore diameter, high treatment temperature, soaking water temperature, and alternating times between cold and heat could weaken the resistance of concentric perforated granite to radial load, but the influence of the deformation pattern on the rock sample was relatively slight. The load–displacement curve during the loading process exhibited the following sections: initial upper concave, short straight line, slowly ascending platform, approximately straight line, short upper convex curve, and post-peak cliff descending sections. Based on the theory of biological population growth, the damage variables of the concentric perforated granite were defined, and the analysis revealed that the internal damage of the rock sample experienced a slow-growth deceleration to a critical state. The numerical simulation results of the shape of the broken rock block and the strain on the side of the rock sample were combined. It was found that two concentration zones of vertical tensile-stress effect were formed inside the rock sample under the action of radial load, which led to the germination of tensile microcracks in the interior of the rock sample and resulted in macroscopic failure. In addition, the tensile microcracks were generated inside the concentric perforated granite. First, they propagated from the inner wall of the rock sample in the loading direction and then, along the outer wall in the vertical loading direction. Then, the microcracks spread and penetrated the outer and inner walls of the rock sample to form the macroscopic fracture surface.