Cross-scale evolution law and damage mechanism of voids in longwall goaf

Abstract Under the background of the "dual carbon" strategy, the resource-oriented and high-value utilization of coal-based solid wastes has become the core direction of green transformation in the coal industry. As the key spatial carrier for the in-situ disposal of underground solid wastes, the resource potential of large goaf areas urgently needs to be systematically exploited. Accurately grasping the evolution law and damage mechanism of voids in goaf is a key breakthrough for resolving the coordinated development dilemma of "safe and efficient production—in-situ solid waste disposal—ecological environment protection" in coal mining. Therefore, this paper combines transient electromagnetic (TEM) detection with physical model tests to systematically investigate the spatiotemporal distribution characteristics, cross-scale evolution law and damage mechanism of voids in longwall goaf. The results show that: The void development degree in longwall goaf decreases with the increase in vertical distance from the coal seam following a polynomial function. Controlled by the deformation of the mining-induced lower key stratum, the caved rock mass in goaf undergoes a dynamic evolution process of "caving bulking—deformation contraction—full compaction", and the spatiotemporal evolution of voids in the caved zone is highly coupled with the fracture movement of the lower key stratum and the stress distribution of the floor, exhibiting an obvious three-stage variation characteristic. The void development in the caved zone is characterized by significant zonal differentiation, prominent boundary effects and remarkable control by overburden movement, among which roof structure movement and stress transfer are the direct inducements driving the dynamic variation of voids in the caved zone. Furthermore, it is revealed that the voids in goaf serve as the deformation space for the continuous instability of the overburden and ground surface. The damage effects are mainly manifested in two aspects: inducing continuous large deformation of the lower key stratum structure and generating residual subsidence damage, and the occurrence mechanisms of the two types of damage are clarified. The research results can provide theoretical support and reference for the efficient utilization of goaf space resources in longwall mining and the prevention and control of mining-induced damage.