Research on coordinated damage conduction of overburden-surface in large mining height working faceof shallow coal seam

Studying the chain conduction relationship between strata movement and surface damage in large mining height working faces is of great significance for the “rational development of coal resources, regional environmental protection, and ecological restoration” in western high-intensity mining areas. Based on the key stratum theory, three types of typical physical similarity experimental models for large mining height working face were constructed, and the structural characteristics, moving types, and alternating evolution laws of the key strata were obtained through experiments. Through theoretical analysis, the coupling mechanism between key stratum structure and damage conduction was revealed, and the spatial distribution patterns and dynamic evolution characteristics of damage conduction paths were clarified. Finally, combined with field investigations, the correlation between overburden movement patterns and surface damage characterization was established. The results show that the key strata structure of large mining height working face is mainly divided into “cantilever beam” structure, “voussoir beam−cantilever beam” structure and “double voussoir beam” structure. Type Ⅰ and Ⅱ working faces generally form a “cantilever beam” structure after the key strata in the overburden collapse zone break. The movement and development process of this structure is not invariable, but there is an alternative evolution phenomenon most of the time, which shows the alternative breaking movement of various structural forms such as “cantilever beam”, “step voussoir beam” and “voussoir beam”. The damage conduction in the working face where the key stratum forms a “cantilever beam” structure exhibits instantaneous mutation and single-path characteristics. The damage conduction in the working face where the key stratum forms a “voussoir beam−cantilever beam” structure exhibits characteristics of lower layer triggering, upper layer regulation, and multi-path step transition. The damage conduction in the working face where the key stratum forms a “double voussoir beam” structure exhibits multiple regulation and internal dissipation characteristics. During the alternating evolution of the “cantilever beam” structure of the key stratum, the damage conduction path transitions from single-channel mutation to layered progression. In Type Ⅰ working faces, the sliding instability of the single primary key stratum induces a full-thickness shear failure of the overburden strata and surface, accompanied by the formation of collapse-induced surface fractures. In Type Ⅱ working faces, the rotational instability of the primary key stratum induces a full-thickness fissure penetration failure of the overburden strata and surface, accompanied by the formation of tensile-induced surface fractures. In Type Ⅲ mining faces, the low-angle fracture hinge of the primary key stratum induces bending-subsidence failure in the overlying strata and surface, characterized by predominantly continuous deformation with localized tensile-induced surface fractures. The alternating evolution of the cantilever beam structure in sub key strata induces block superposition and dislocation, which transfers through the primary key stratum to the surface, resulting in dislocation-propagated surface fractures abnormally developed in Type II working faces.