The mechanical evolution behaviors and failure mechanism of rock-like specimen containing complex shape goaf

A iron mine in Xinjiang has left a huge goaf after years of mining. The stability of rock mass around goaf is very important to the safe mining of the whole mine. In order to study the structural stability of rock mass around goaf, and 10 sections of the goaf are selected and its fractal dimensions are calculated. Combined with 3D printing technology, rock-like specimens containing goaf (RCG) are made, tests and PFC numerical simulation are carried out, and the mechanical properties, energy consumption characteristics, and damage evolution of RCG are analyzed. The results show that: (1) The mechanical properties of RCG are closely related to the fractal dimension (FD) of goaf. The peak stress, peak strain, and elastic modulus are linearly negatively related to the FD. (2) The absorbed total energy and the stored elastic energy have strong correlation with FD. The energy evolution process of RCG is as follows: RCG slowly absorbs energy to compact the specimen; RCG quickly absorbs energy for storage; RCG quickly releases elastic energy stored inside. (3) The concentrated stress of RCG is 4-6 times of the axial stress, and the crack initiation and propagation are driven by the concentrated stress. The RCG show the through-shear failure starting from the stress concentration zone and developing along the diagonal. (4) The damage evolution process of RCG can be divided into four stages: the stress rises slowly, the damage ac-cumulates slowly, and the damage rate is at a low level; the stress rises rapidly, and the damage accumulates rapidly and the cumulative speed continues to increase; the stress decreases rapidly, and the damage continues to grow at a high level, but the damage accumulation speed decreases rapidly; the damage increases slowly at a high level, and the damage rate decreases slowly and tends to zero.