Objective  This study aims to explore the synergistic breaking responses and energy evolution mechanisms of composite key strata under mining disturbances. These efforts will provide robust theoretical support for the prevention and control of disaster-causing accidents in the surrounding rocks of coal seams and hold great significance for ensuring safe mining operations underground.

Methods  The breaking and instability characteristics of composite key strata under mining disturbances were analyzed by integrating physical simulation using similar materials, numerical calculation, and theoretical analysis. Accordingly, the accumulation and release patterns of strain energy and gravitational potential energy in the overburden were investigated. Finally, the energy evolution mechanisms of the overburden under the stimulation of key stratum breaking were elucidated.

Results  During the mining along the mining face with composite key strata, the breaking and movement processes of the lower and upper key strata are contained and influenced by each other, serving as the intrinsic cause of intense rock pressure behavior in coal seams of such mining face. Following the excavation of the mining face, the instantaneous breaking of the lower key stratum produces an instantaneous unloading effect on the upper key stratum. Meanwhile, the instantaneous breaking of the upper key stratum imposes a dynamic impact on the lower key stratum. These interactions result in different breaking modes of individual key strata under mining disturbances, i.e., cutting-induced and rotary instability, while the composite key strata undergo synergistic rotary instability and overall cutting-induced instability. These different breaking modes lead to significantly distinct energy accumulation and release characteristics of the overburden. Specifically, in the case where the lower key stratum undergoes rotary or cutting-induced instability, the overburden in the stope releases roughly the same elastic strain energy, while the gravitational potential energy released by the overburden under cutting-induced instability exceeds that under rotary instability. Consequently, low-frequency and high-energy microseismic events occur in the overburden. For the synergistic breaking of both key strata, the energy consumed by the coal seams and rocks equals the total energy released by both key strata, with the overburden releasing more gravitational potential energy than elastic strain energy. For the overall cutting-induced instability mode, the gravitational potential energy released by the overburden acts as the main source of energy consumed by the coal seams and rocks. The dynamic disturbance to the mining face under such a breaking mode is significantly more intense compared to the case of the breaking of individual key strata, leading to large and small periodic weighting in the mining face with composite key strata.

Conclusions  The intense rock pressure behavior in the mining face with composite key strata is essentially caused by the breaking with mutual feedback mechanisms of the upper and lower key strata. The prevention and control of disaster-inducing accidents in underground coal mines should focus on cutting off the energy superposition paths between the upper and lower key strata. Specifically, it is necessary to analyze and predict the breaking modes of key strata using means such as microseismic event monitoring and the monitoring of the working resistance of supports. Accordingly, differential and advance intervention measures should be adopted to shift from passive support into proactive energy control. The purpose is to prevent the concentrated release of the superimposed substantial gravitational potential energy and strain energy from the composite key strata, thereby fundamentally mitigating the intense dynamic disturbances induced by large and small periodic weighting.