Investigation on fracture characteristics and failure pattern of inclined layered cemented tailings backfill

The fracture characteristics of the layered cemented tailings backfill (LCTB) as an artificial false roof in un-derhand cut-and-fill mining would directly affect the personal safety of workers. For this reason, the non-layered cemented tailings backfill (NS-CTB), 2-layered (2-S), and 3-layered (3-S) LCTB with 0, 5, and 10 layered angles (LA) were prepared respectively for three-point bending experiments, and the microscopic crack evolution law and failure mode were simulated and analyzed by PFC 3D. The results revealed that the flexural strength (FS) and peak deflection (PD) of the LCTB decreased with the increase of the number of layers (NL), and the rate of decline increased gradually. The bending modulus (BM) and post-peak toughness (PPT) of the LCTB gradually rise with the increase of the NL. The FS and PD of the LCTB were inversely correlated with the LA, the BM and PPT tended to decline first and then increase, and reached the lowest when the LA was 5. When the LA is greater than 5, the bearing structure of the LCTB changes greatly, and the FS and PD of the LCTB have indeed fallen substantially. The numerical simulation results reveal that at the initial loading stage, the LCTB merely breaks and produces a small amount of cracks at the loading point in contact with the wall and layered contact surface. When the LCTB approaches the FS, a large number of cracks are generated and penetrate the LCTB, and then the total number of cracks curve enters the stable stage. All groups of CTB are destroyed by the lower part in tension initially, and then the cracks expand upward through the CTB, culminating in macroscopic failure to the CTB. The cracks of the NS-CTB expand in a smooth curve, while the cracks of the LCTB expand to the intersection of the layered contact surface and the loading direction with an obvious inflection point, and expand downward along the layered contact surface. Finally, this research explores the macroscopic fracture characteristics and microscopic failure patterns of non-horizontally LCTB, and the results of this study can provide a reference for the design and application of LCTB in the field of underhand cut-and-fill mining.