Prediction on weighting classification of fully-mechanized caving mining under extremely thick coal seam

The numbers of roof accidents and deaths have long occupied an important position in various types of coal mine accidents in China, especially when there are multiple hard stratum in overburden.The structures of multiple hard stratum are systematic and complex, which can easily causes strong strata behavior, even induces dynamic disasters.Therefore, there is an urgent need to develop a method for predicting weighting classification under complex hard rock formations in order to provide a theoretical support for the control of hard rock formations.In this paper, based on the characteristics of fully mechanized top coal caving mining under the conditions of complex hard rock layers, it is determined that the hard rock layers in different spatial positions have different pressure control effects.That is, the low-level hard rock layer controls small-period weighting, the medium-level hard rock layer controls large-period weighting, and the high-level hard rock layer controls strong strata behavior.Based on the theory of plate and shell mechanics and plastic mechanics, a “multi-layer slab structure” system model of hard rock layers was established, and the hard rock layers were divided into near-field cantilever structures and far-field masonry structures, according to the structural form.It reveals that the process of breaking motion of complex hard rock layer has the characteristics of gradual and compound.The criterion of breaking scale of hard rock layer is established, and the method of grading prediction of rock pressure under the condition of complex hard rock layer is formed.Based on the engineering background of fully mechanized top coal caving mining in the Carboniferous ultra-thick coal seam of Datong mining area, the theoretical prediction of weighting classification was carried out.The applicability of the rock pressure classification prediction method under complex hard rock formation conditions was verified by analyzing on-site rock pressure monitoring and micro-seismic monitoring data.The research results have achieved a certain degree of knowability and controllability of complex hard rock formations.However, the mechanism of how energy is transferred to the working face causing dynamic appearance is not fully understood when the structure controlled by different hard rock formations is broken.The study of this problem provides a theoretical support for the precise control of hard rock formations.