Research on Mining-Induced Stress Distribution of Extrathick Coal Seams Based on Electromagnetic Wave CT Technology

Feng Luo,Minghui Li,Guodong Li,Xueqing Li,Tuan He

doi:10.1155/2022/6870207

Abstract

Fully mechanized caving mining in extrathick coal seams is currently the most efficient mining method. To figure out the mining-induced stress in extrathick coal seams which is significantly different from the normal ones is essential for mining safety. This research is based on the No. 3106 working face of Lu-Zi-Gou coal mine in China, which extracts extrathick coal seams by using the comprehensive mechanized top-coal caving method. According to the elastoplastic theory, a multiforce superposition mining-induced stress model is constructed in this research. In this model, the mining-induced stress is generated by the side coal seam of the stope, including the load formed by the broken roof blocks in the caving zone, the unbroken rock layers in the side of the goaf, and the rock layers in the bending zone. To verify the model, electromagnetic wave CT detection and borehole endoscopy are used to test the coal’s electromagnetic wave attenuation and internal joints. The results indicate that the mining of extrathick coal seams forms internal and external stress fields in the side coal seams of the stope. As the depth increases, the mining-induced stress first increases and then decreases within the two areas. According to the above conclusions, the width of coal pillars and the location of roadways between adjacent working faces can be reasonably determined.

Highlights

In Northwest China, there are vast reserves of coal resources
Some coal seams’ thickness exceeds 20 m, which is an extrathick coal seam [1]. e extrathick coal seam provides geological conditions for maximizing coal mining efficiency. e mining of extrathick coal seams is an efficient way of extracting coal resources
According to the distribution of mining-induced stress, the internal and external stress fields of fully mechanized top-coal caving mining in extrathick coal seams can be divided into five areas

Summary

Introduction

In Northwest China, there are vast reserves of coal resources. Some coal seams’ thickness exceeds 20 m, which is an extrathick coal seam [1]. e extrathick coal seam provides geological conditions for maximizing coal mining efficiency. e mining of extrathick coal seams is an efficient way of extracting coal resources. Due to the lack of long-term, stable, and effective technology and equipment for monitoring mining-induced stress and surrounding rock damage [7], physical simulation, numerical simulation, and theoretical modeling are often used to study the distribution and evolution of mininginduced stress under the condition of comprehensive topcoal caving mining in the extrathick coal seam [8]. Kumar et al and Mandal et al conducted field research on Zero coal seams in Kajora area of which the thickness was more than 7.0 m It showed that the mining of extrathick coal seams caused different surface subsidence and crack distribution [12, 13]. The research of the distribution and evolution of mining-induced stress needs to be further studied under the condition of fully mechanized top-coal caving in the extrathick coal seam. In the process of fully mechanized caving mining in extrathick coal seams, the evolution process of mining-induced stress is analyzed

Distribution of Mining-Induced Stress in the Extrathick Coal Seam

40 Internal stress filed

Field Test

H: Burial depth of the coal seam h