Investigation on the breakdown characteristic and crack extension mechanism of heat-treated granite under cycle hydraulic fracturing

Abstract

To address the lack of research on breakdown characteristics of heat-treated rock under cyclic hydraulic fracturing (CHF). In this study, the breakdown mechanism and crack characteristics of heat-treated granite under CHF are investigated using a combination of experimental research and numerical simulation methods. CHF induces specimen fatigue and increases the number of hydraulic fracture branches on specimen surfaces compared to traditional hydraulic fracturing (THF). With the elevation of heat treatment temperature, the hydraulic fracture network on the surface of CHF samples becomes increasingly intricate, accompanied by a rise in hydraulic surface micro-cracks and roughness. CHF effectively reduces accumulated AE energy during the fracturing process by converting high-energy AE events into numerous smaller, low-energy events compared to THF at the same heat treatment temperature. Under CHF, both peak AE amplitude and cumulative AE energy decrease with increasing heat treatment temperature. The rupture of heat-treated granite under CHF is influenced by the coupled effects of thermal stress and alternating pore pressure.