Objective In the mining process of coal mines, the cyclic loading and unloading effects caused by multiple mining disturbances can alter the mechanical properties of coals, serving as a significant cause of rock bursts. Revealing the response characteristics of crucial mechanical parameters and the damage mechanisms of coals can provide a basis for discriminating the impact-induced instability state, holding great significance for enhancing disaster prediction capabilities.

Methods Quasi-static uniaxial cyclic loading and unloading experiments and the dynamic impact loading experiments on large-size coal-like specimens were combined to accurately capture the stress, strain, and acoustic emission responses during the experiments, thoroughly unveiling the laws of changes in mechanical parameters and the damage evolutionary processes of the specimens under the action of multiple mining disturbances.

Results and Conclusions  Key findings are as follows: (1) The maximum load is identified as the most critical factor influencing the mechanical properties of the coals damaged by multiple cyclic loading and unloading processes. With an increase in the number of cycles, the specimen in the yield stage under loading displayed increasing, decreasing, and then increasing residual strain. Meanwhile, it exhibited gradually increasing dissipated energy density and acoustic emission characteristic value corresponding to the maximum load, suggesting escalating damage degrees of the specimens. For the specimen in the elastic stage under loading, all the mechanical parameters mentioned above first decreased and then increased. In contrast, for the specimen remaining in the compaction stage throughout the experiment, the three sets of data manifested gradually decreasing trends. (2) Under dynamic impact loading, all of the three specimens experienced impact-induced failure. The specimen subjected to a lower load in the earlier quasi-static cyclic loading and unloading experiments exhibited less damage, higher dynamic load strength required for impact-induced failure, and higher elastic moduli corresponding to the failure at peak strength. (3) The damage degrees of the specimens were characterized from both strain and energy perspectives. A comparative analysis revealed that energy damage degrees proved more sensitive in discriminating the damage degrees of the specimens in the experiment process. (4) Observations of the impact fracture characteristics inside the specimens suggest that the specimens experienced the quiet, particle ejection, stability failure, and impact-induced failure stages in the process of impact-induced failure. (5) The value of residual strain, when it began to increase, in the late stage of cyclic loading and unloading, as well as the early stage of stability failure in the impact-induced failure process can be used as early-warning information for the impact-induced instability of damaged coals. This study, having obtained the evolutionary patterns of the mechanical properties of coals subjected to multiple mining disturbances, can provide a theoretical basis for determining the impact-induced instability state of damaged coals in engineering construction. Furthermore, it holds great significance for promptly identifying the potential instability risks of damaged coals and thereby optimizing the supporting schemes and ensuring the safe mining of mines.