Cooperative Failure of Overburden-Surface and Its Control Measures in Longwall Mining

The failure form of overburden and surface is an important basis for developing mining damage control and ecological restoration measures. For high-intensity mining, the failure forms were divided into three categories to analyse the breaking law of key strata, the form of structural instability, the development characteristics of water-conducting fractures, and the dynamic evolution process of surface cracks through the UDEC numerical simulation and field observation. The results indicate that the whole cutting of overburden leads to the formation of step-like ground fissures (sinkholes) with large height difference when the surface in the caved zone with single key stratum. The primary key stratum forms the step beam structure and loses stability periodically when the surface in the fracture zone. The distribution of ground fissures is mainly tensile type, supplemented by step-like ground fissures with a relatively small height difference. The primary key stratum fracture incompletely, and forms tensile ground fissures with small width and “self-repaired” when the surface in the sagging zone. Then the effective control measures can be proposed based on the summarized damage level of production safety and ecological environment in high-intensity mining.