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1. Local roof accident
The characteristics of local roof accidents are as follows: First, the scope is small, and the number of casualties is small (1-2 people). The location of the roof accident is mostly where people work. Cause of such accidents is damage to the roof have been caused by the loss of relying on, is part of the reason that triggered the process, failed to support the exposed roof of broken coal mining work (including broken coal, coal loading, etc.); the other is Partial caving accidents that occur during column operations.
2, large area cut top surface accident
The characteristics of such accidents are large areas, fierce and serious consequences, which not only seriously affect production, but also lead to major personal injuries. The cause of the accident was caused by large-scale movements of the direct roof and the old roof.
Face-to-face accidents caused by direct top movement can be divided into two categories in terms of the starting direction of their forces:
(1) Push-type accidents. Including the propensity to push the type of accident that tends to advance the work surface and the push-type accident that is easy to occur in the direction of the goaf. This type of accident is characterized by a large thrust in the direction parallel to the coal seam when the roof movement occurs, and the collapse of the unstable bracket causes a kneading accident.
(2) Pressure-type accidents. This includes crushing in the direction of the coal wall and crushing in the direction of the mining area. This type of accident is mainly caused by the force acting perpendicular to the direction of the top and bottom, the bracket with insufficient bending and bending force, or the pressing of the bracket into the low compressive strength plate. The kneading accident caused by the old top movement can be divided into two categories according to the nature of the force and the starting direction:
(1) Impact push type accident. The accident is characterized by the fact that the old top of the starting movement first applies its force to the direct top of the separated layer near the coal wall, causing the coal wall to collapse and the top plate to be cut, and then the high-speed moving old top pushes the roof directly.
(2) Pressure-type accidents. Such accidents occur on the working face of the pillars. Because the wooden pillars with little shrinkage can not resist the pressure of the old roof, they are broken in turn during the sinking process of the old roof. As a result, the support strength of the remaining pillars is not enough to be flattened by the force of the smooth direct top. Causing a face accident.
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