Abstract
Rock bursts in coal mines are usually unpredictable. In view of this problem, the energy–frequency relationship and spatial distribution characteristics of microseismic events during the mining of 5305 working face in Xinhe Coal Mine under complex geological conditions were analyzed in this study. Besides, the law and precursors of rock burst occurrence in this working face were discussed. The following research results were obtained. Before the rock burst occurred in 5305 working face, the energy and frequency of microseismic events vary in the following order: “peak-drop-rise-rock burst.” The analysis on spatial characteristics of microseismic events suggests that microseismic events were mainly concentrated at the boundary between the roof and the coal seam or at the hard roof near the coal seam within 0–160 m in front of the working face, and most of the events lay on the goaf side. Moreover, the energy and frequency of microseismic events both decrease in the above region before the rock burst occurred. This “microseismic event absence” phenomenon can be regarded as one of the precursors of rock burst occurrence. In addition, a multilevel antiburst scheme was proposed for the complex conditions: (1) to adopt large-diameter boreholes pressure relief technology and key layer high-level pressure relief technology for adjusting the stress distribution in the surrounding rock of crossheading in front of the working face and dissipating elastic strain energy; (2) to determine the advance speed to be 1.5 m/d for reducing the mining disturbance; (3) to adopt full-section reinforced support of the roadway for enhancing the antiburst capacity of surrounding rock. After the implementation of this scheme, the energy and frequency of microseismic events monitored on-site changed gently, and 5305 working face was safely recovered to the stop line position. The scheme boasts a remarkable rock burst prevention and control effect.
Highlights
A rock burst, a serious coal and rock dynamic instability disaster in coal mining, usually features suddenness, destructiveness, and complicated mechanism
(i) on August 6 and August 16, 2007, two consecutive major rock burst accidents occurred in Crandall Canyon Coal Mine in Utah, USA, causing 9 deaths and 6 injuries; (ii) in 2008, the “6∙5” rock burst accident occurring in Qianqiu Coal Mine in Henan Province, China, resulted in an instantaneous uplift of nearly 100 m of the roadway
Among the 20 trapped miners who were working 9 were killed and 11 were injured; (iii) in 2018, the “10∙20” major rock burst accident occurring in Longyun Coal Mine, Shandong Province, China, led to 21 deaths and severe destruction of nearly 100 m roadway
Summary
A rock burst, a serious coal and rock dynamic instability disaster in coal mining, usually features suddenness, destructiveness, and complicated mechanism. Legge and Spottiswoode [16] believed that the B-value variation in the Gutenberg–Richter formula was greatly influenced by blasting, but it could reflect the regional geometric changes in rock fracturing around the working face These changes would exert a certain effect on the rock burst risk. In this study, considering complex conditions such as hard roof, hard coal seam, asymmetric mining, and many roadways (hereafter referred to as the “two-hard” complex conditions) in 5305 working face of Xinhe Coal Mine, the spatial distribution evolution of microseismic events was investigated based on the information acquired by the microseismic monitoring system. A multilevel antiburst scheme was proposed for the “two-hard” complex conditions. e research results provide a valuable reference for rock burst monitoring in other working faces
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