Abstract
Roof sliding and instability along the coal wall usually occur in the working face at large mining heights during the process of the first weighting, which causes roof cutting and support crushing. A mechanical model consists of the main roof, immediate roof, and support based on the nonlinear characteristics of the failure and instability of the immediate roof under the abutment pressure, which we constructed to study the step sinking of the main roof, as well as to assign the reasonable value of the support resistance during the first weighting. The instability mechanism of the system was studied by the catastrophe theory and the principle of energy conservation. A conclusion was drawn that the combined cantilever beam structure for the immediate roof will form with the increase of the mining height, and the instability of the immediate roof causes the catastrophic instability of the system. The system instability was found to be related to the stiffness ratio K, material parameters, the load Q, and the first weighting interval of the main roof by analyzing the necessary and sufficient conditions for system instability. The influence degree of each parameter on the stiffness ratio K was as follows: elastic modulus E > support stiffness k1 > cross-section area a > immediate roof thickness H. The calculation equations of support resistance and subsidence of roof step were obtained. The method of judging the roof instability using catastrophe theory was proved as reasonable on the basis of the monitoring example of no. 12401 working face in Shendong mining area, China. On this basis, a reasonable value of support resistance was further calculated, and the working face was maintained safely when the support resistance exceeded 19,232 kN.
Highlights
Shallow coal seams are widely distributed in the northwestern territory of China, which is characterized by shallow burial depth, thin bedrock, and an overlying thick and loose sand layer [1].The mining height of coal seam is increasing, reaching a maximum of 8.8m at present with the continuous improvement of fully mechanized mining degrees, which makes the goaf space formed by coal seam mining increase constantly
It is of great significance to study the relationship between the support and the surrounding rock during the first weighting of working face, as well as to analyze the mechanical mechanism and key disaster-causing factors of the main roof step sinking along the coal wall to provide the determination method of the support resistance, which has an important role in ensuring the safety of the working face
The structural characteristics and instability process of the first weighting in large mining height working face were analyzed through a physical experiment and a numerical simulation, performed in order to study roof sliding and instability along the coal wall during the first weighting in the working face with large mining height in shallow coal seam
Summary
Shallow coal seams are widely distributed in the northwestern territory of China, which is characterized by shallow burial depth, thin bedrock, and an overlying thick and loose sand layer [1]. It is of great significance to study the relationship between the support and the surrounding rock during the first weighting of working face, as well as to analyze the mechanical mechanism and key disaster-causing factors of the main roof step sinking along the coal wall to provide the determination method of the support resistance, which has an important role in ensuring the safety of the working face. The main objective of this study was to explore the general process and weighting characteristics of of the the main mainroof roofalong alongthe thecoal coalwall wallduring duringthe thefirst firstweighting weighting large mining height ofof large mining height in in shallow coal seam, analyzethe themechanical mechanicalmechanism mechanismof ofthe themain main roof roof instability, instability, to reveal the shallow coal seam, toto analyze disaster‐causing determination method of support resistance to ensure the disaster-causing factors, factors,and andtotoexplore explorethe the determination method of support resistance to ensure stability of working face.face.
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