Structural Evolution and Motion Characteristics of a Hard Roof During Thickening Coal Seam Mining

Xiangyang Zhang,Xiangyang Zhao,Lei Luo

doi:10.3389/feart.2021.794783

Xiangyang Zhang, Xiangyang Zhao + Show 1 more

Open Access

https://doi.org/10.3389/feart.2021.794783

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Abstract

This study combined theoretical analysis, physical simulation, and numerical simulation to discuss the influences of the structural evolution and motion characteristics of a hard roof during thickening coal seam mining on working face pressure. Results showed that during the mining of the thickening coal seam with a hard roof, the settlement curve of low-level strata was a stepwise wave slope, and the settlement curve of high-level strata shifted from a “V-shaped” distribution pattern to a parabola under the full mining of the coal seam. When the mining thickness was relatively small, the mining space expanded with the increase in mining thickness due to the “masonry beam” structure formed by the low-level, sub-critical overlying strata. The low-level critical strata formed a “composite cantilever beam” structure with a hard immediate roof after advancing into the caving zone. After complete recovery, the overlying strata were in a steady-movement state, and the plastic failure zone of the overlying strata of the thickening coal seam presented obvious distribution characteristics of longitudinal and transverse partitions. This study provides theoretical reference for coal seam mining under similar geological conditions.

Highlights

Decades-long production practices have shown that the caving height of overlying strata in a goaf increases, and the sphere of influence of the overlying strata on the working face pressure expands as the disposal mining thickness increases in fully mechanized caving mining of thick coal seams
A physical simulation test was designed to compare the structural differences of the critical overlying strata during thickening coal seam mining under the same overlying conditions and to verify the above-mentioned discriminant formula
With the increase in mining thickness, the available rotary volume of the masonry beam blocks formed by sub-critical stratum 1 exceeded the ultimate value, resulting in rotary deformation buckling of the low-level masonry beam structure

Summary

Introduction

Decades-long production practices have shown that the caving height of overlying strata in a goaf increases, and the sphere of influence of the overlying strata on the working face pressure expands as the disposal mining thickness increases in fully mechanized caving mining of thick coal seams. During the mining of a thickening coal seam with a hard roof, the structural morphology and motion characteristics of the hard immediate roof and sub-critical strata change with coal seam thickness. A physical simulation test was designed to compare the structural differences of the critical overlying strata during thickening coal seam mining under the same overlying conditions and to verify the above-mentioned discriminant formula.

Results

Conclusion