Mechanical behaviour and fracture characteristics of layered composite rocks containing parallel pre-flaws under dynamic loading

During deep excavation or mining, layered composite rocks (LCRs) with defects are common. Localised deformation and collapse often occur at rock interfaces and within defect zones. To this end, we conducted dynamic impact tests on layered composite rocks containing defects. This study aimed to investigate the effects of the interlayer strength ratio and pre-flaws on the dynamic mechanical behaviour and fracture characteristics of the rocks. Research results indicate that: (1) The dynamic compressive strength of layered composite rocks containing defects increases with the rise of the strength ratio, while an increase in the inclination angle of pre-flaws causes it to first decrease and then increase. When the inclination angles are 45° and 90°, the dynamic compressive strength reaches its minimum and maximum values, respectively. (2) When the strength ratio is 1.34, the failure of the specimen is determined by the defect angle; when the strength ratio increases to 2.53, the failure of the specimen is governed by the weaker rock. (3) The crack propagation modes in the specimens are categorised into three types: initiation from the strong side tip, initiation from the weak side tip, and propagation from the weak side to the strong side.