Investigation on the Movement and Fracture Characteristics of an Extra-Thick Hard Roof during Longwall Panel Extraction in the Yima Mining Area, China

Hongwei Wang,Yaodong Jiang,Shuo Xu,Daixin Deng,Guozhen Yang,Ruiming Shi,Hualei Zhang

doi:10.1155/2021/4092242

Abstract

As an extra-thick hard roof is a significant contributing factor to frequently induced sudden roof collapse accidents and coal bursts, this study investigates the relationship between extra-thick hard roof movement and mining-induced stress using physical experiments and numerical simulation methods based on mining activities in a longwall panel in the Yima mining area, Henan province, China. The results suggested that the movement and failure processes of the extra-thick roof could be divided into three main periods: the undisturbed, movement stabilization, and sudden collapse periods. The roof displacement remained essentially unchanged during the undisturbed period. During the movement stabilization period, the displacement gradually increased into the upper roof. However, the extra-thick main roof remained undisturbed until the immediate roof experienced its fourth periodic caving in the physical model. Consequently, the displacement expanded rapidly into the extra-thick main roof during the sudden collapse period and the strain energy was violently released when it accumulated in the extra-thick main roof. Additionally, the mining-induced stress was characterized by a sudden decrease in the gradual increase trend when the extra-thick roof instantly collapsed. The deformation and fracture of the extra-thick roof could cause a sudden decrease in the mining-induced stress and lead to continuous and unstable subsidence pressure exerted on the mining panel and roadway. This significantly contributes to the occurrence of coal bursts.

Highlights

An extra-thick hard roof is the strata with large thickness and high strength occurring above a coal seam or a thin immediate roof
The deformation and fracture of the extra-thick roof could lead to the continuous and unstable subsidence pressure exerted on the mining face and roadway, which provided a continuous force to the immediate roof, and coal seam and could cause a sudden decrease in the mininginduced stress of the extra-thick roof
(1) The movement and failure processes of the extrathick roof could be divided into three main periods: the undisturbed, movement stabilization, and sudden collapse periods

Summary

Introduction

An extra-thick hard roof is the strata with large thickness and high strength occurring above a coal seam or a thin immediate roof. Large area movement and unstable fracture of the extra-thick hard roof are significant hazards threatening safe production in coal mines. It will cause extensive damage to the entire stope and is an important factor of inducing typical dynamic disasters such as coal bursts [1,2,3]. A sudden and violent collapse of the extra-thick hard roof can release masses containing deformation energy and cause coal bursts during longwall panel advancement where machinery and workers assemble. The frequent extra-thick roof collapse events caused by mining activities have made an important influence on the safety of coal mine production for several years. The accident occurrence was related to the F16 thrust fault near the mining panel, the presence of a 550 m thick and hard conglomerate rock above the coal seam was a key disaster factor. Dynamic movement evolution of the extra-thick roof is of primary interest in this study

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Conclusion