Mechanism Of The Movement Of Cantilever Beam Structure On End Face Leakage

Under the conditions of ultra-high mining height, the first key layer of the overburden is often easy to directly enter the collapse zone and break to form a "cantilever beam" structure. The movement state of this structure will obviously be different from the movement state of the "masonry beam" structure of the key layer under the general low mining height, and the effect on the lower direct roof will also be different. Therefore, the following is an analysis of the mechanism of the breaking movement of the "cantilever beam" structure of the overburden key layer of the ultra-high mining height fully mechanized mining face on the end face leakage. [1]
When the key layer is exposed for a certain length and breaks, its fracture line will generally advance the working face by a certain distance; at this time, due to the restriction of the coal and rock mass in front of the coal wall, the fracture block of the key layer can only rotate at a small angle and reach a temporary stable state; at the same time, under the action of the rotation and extrusion of the fracture block, the direct roof will also produce a tensile fracture zone and a compression deformation zone ("two zones") near the fracture line of the key layer and the end face of the working face respectively. As the working face continues to advance, the rotation angle of the key layer fracture block gradually increases, and the range of the "two zones" also increases accordingly, accompanied by end face leakage caused by the compression deformation zone. When the working face pushes over the key layer fracture line, since the broken block A in the rear collapses directly into the goaf, it cannot form a lateral constraint on the broken block B in front, so the block B will never be able to form a self-stable bearing structure during the rotation process; when the initial support force of the support is insufficient during the working face frame shifting process or the load on the block B is large, the block will be unstable and displaced along the fracture line, resulting in the direct penetration of the "two zones" on the top, forming the most dangerous through-type end face leakage phenomenon. In this process, the support resistance will also increase rapidly with the sinking of the roof rock layer. When its resistance is sufficient to balance the load of the key layer "cantilever beam" broken block B and its overlying collapse zone rock layer, block B will be able to achieve stability. Since this process lasts for a short time, although block B undergoes unstable displacement, the shrinkage reflected on the support column will not be obvious.