Abstract
Ultra-thick hard sandstone roofs present high thickness, poor delamination, and wide caving range. The strata pressure of the working face during actual mining increases, having a significant influence on the safe mining of the working face. Especially, in the mining areas of western China, the fully mechanized mining faces with high mining height and high-strength mining are more prominent. Understanding the fractures and stress evolution characteristics of the ultra-thick hard sandstone roof during actual mining is of high significance to control the dynamic pressure on the working face. In this paper, the typical ultra-thick hard sandstone roof of the Xiaojihan coal mine was taken as an example. The structural and chemical composition characteristics were analyzed. Besides, the fracture characteristics of ultra-thick hard roof during the working face mining were analyzed. Moreover, the fracture structure consistency was verified through physical simulation and a field measurement method. Finally, the stress evolution laws in the ultra-thick hard sandstone roof fracture were studied through numerical simulation. The findings demonstrated that (1) the ultra-thick hard sandstone roof was composed of inlaid coarse minerals, which had compact structure, while the Protodyakonov hardness reached up to 3.07; (2) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof had the characteristics of brittle fracture, with a caving span of 12 m; (3) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof followed the stress evolution laws that were more sensitive to the neighboring goaf. Therefore, it was necessary to reduce the fracture span or layering of ultra-thick hard sandstone roof through the manual intervention method adoption or increase either the strength of coal pillar or supporting body, to resist the impact generated during ultra-thick hard sandstone roof fracture.
Highlights
Coal still constitutes the main fossil fuel for energy production throughout the world
In China, up to 36 pairs of mines exist, of tens of millions tons in capacity, while 34 pairs are under construction or being expanded. Most of these mines are distributed in the mining areas within western China, demonstrating the characteristics of highintensive mining, such as having working faces with large mining height, high advance speed, and long advance distance [1]
Guo [8] and Ning [10] successfully solved the problem of severe strata behaviors, caused by ultra-thick hard roofs, through the decompression blasting and deep-hole presplitting blasting methods, respectively
Summary
Coal still constitutes the main fossil fuel for energy production throughout the world. Guo [8] and Ning [10] successfully solved the problem of severe strata behaviors, caused by ultra-thick hard roofs, through the decompression blasting and deep-hole presplitting blasting methods, respectively He [21] and Zheng [22] relieved the early-warning of high strata pressure on the working face, guaranteeing safe mining at the working face through the hydrofracturing and sleeve fracturing methods, respectively. Scholars, both domestically and abroad, conducted research on hard roofs, mostly from the perspectives of mine pressure model, energy aggregation, and rock strata movement, through the methods of numerical simulation and theoretical analysis. Through the 11215 fully-mechanized mining face in the Xiaojihan coal mine consideration as an example, the roof fracture and stress evolution characteristics during mining in the fully-mechanized mining face, under the condition that the ultra-thick sandstone roof was near goaf, were revealed through the methods of theoretical analysis, similar simulation, numerical simulation, and field measurement. is provided the important theoretical basis for the overlying strata control and roadway support at the working face under this condition
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