Study on the composite fracture characteristics of filling and reinforcing cracked rock mass after high temperature damage

Abstract Underground tunnel fire will cause loss to the surrounding rock mass and induce structural damage, which seriously threatens the safety of tunnel excavation engineering. Studying the fracture characteristics of high‐temperature rock mass after grouting has important guiding value for the restoration of underground tunnels after fire. In this study, cracked straight‐through Brazilian disc (CSTBD) gabbro samples were first heat‐treated at 25, 200, 340, 500, 600, and 800°C. The prefabricated cracks of gabbro were then cemented with cement slurry. The deformation and failure processes were measured using digital image correlation (DIC) technology. The research shows that the peak load of rocks is reduced due to thermal damage caused by high temperature, and the unfilled samples with β = 90° reach a minimum of about 7 kN at 800°C, which is only 44% of that at normal temperature. 600°C is the threshold temperature for significant changes in fracture toughness and thermal damage of gabbro samples. The filled cement bears part of the compressive stress and shear stress, weakens the stress concentration, and the sliding friction with the rock contact surface inhibits the initiation of cracks, thereby increasing the bearing capacity of the specimen. The study provides some reference for grouting restoration of the rock mass after a tunnel fire.