The fracture mechanism and precursors of rock instability induced by unloading are crucial for geological disaster control. Taking 400 mm × 400 mm × 400 mm marble as an example, this work investigated the damage evolution and acoustic emission (AE) behavior of unloading-induced large-scale rock fracture. The results showed that the rock fracture induced by double-face unloading is strain-type fracture. The rock damage induced by unloading exhibits anisotropy, which increases with the unloading damage level. Microcracks induced by double-face unloading are mostly tensile, and more shear cracks occur near the unstable state. Tensile cracks are mainly distributed near the free surface and fracture surfaces are nearly parallel to free surface. Shear cracks are mainly distributed inside the rock and fracture surfaces are oblique to the maximum stress direction. The AE signals of large-scale rock fractures are characterized by medium-low frequency and medium-low amplitude. The occurrence of high-count, high-energy AE signals, and the increase of AE events are the precursors of unloading-induced rock fracture. This article is not only a useful supplement to the theoretical system of rock damage evolution and fracture precursors, but also provides new ideas for the prevention and control of underground engineering disasters caused by unloading.
Chen et al. (Mon,) studied this question.