Macro‐meso damage cracking and volumetric dilatancy of fault block‐in‐matrix rocks induced by freeze–thaw‐multistage constant amplitude cyclic (F‐T‐MSCAC) loads

Abstract In this study, we experimentally investigated the mechanical behaviors of a fault unwelded bimrock exposed to first freeze–thaw weathering and then disturbed stress conditions. The impact of freeze–thaw damage on volumetric deformation, damage propagation, and mesoscopic instability mode was studied. Test results show that the block‐matrix interface cracking easily occurs after freeze–thaw treatment. The strain rate increases with the increase of the freeze–thaw cycle, and an early instability precursor is issued from the evolution of volumetric strain rare. In addition, a coupled evolution model considering the mechanical damage and the freeze–thaw weathering damage was defined, and it was suggested that the model pattern has obviously correlation with the occurrence of freeze–thaw damage. Moreover, posttest CT scanning revealed the influence of freeze–thaw on meso‐cracking and volumetric dilatancy pattern. It is found that the block contact, interlocking, occlusion, and separation contribute a lot to bimrock volumetric expansion.