Abstract
At present, coal bursts in working faces of steeply inclined coal seams (SICSs) have rarely been investigated, and current research focuses on the influences of roof breaking and instability of overlying structures in goaf on coal bursts; however, the stress state of coal masses in working faces being subjected to coal bursts is rarely researched. To overcome the above defects, a model for analysing stresses on coal masses in horizontal section of SICSs was established based on the coal burst that occurred in LW5521-20, Yaojie No. 3 Coal Mine, Lanzhou, Gansu Province, China. Moreover, the mechanism underpinning such a coal burst in SICSs was analysed based on the superposition mechanism of dynamic and static loads. The results show that the side abutment pressure near the roof and floor under the horizontal sections of SICSs is asymmetrically distributed in the vertical direction in which the peak of side abutment pressure near the roof is closer to the working face and therefore is taken as the source of static loads for coal bursts in working faces. When the superimposed dynamic load caused by hanging roof breaking and high static load borne in the coal masses is larger than the critical load for coal burst inception, a coal burst will occur. Furthermore, the superimposed dynamic load induced by coal bursts on the support and the initial static load on the supports are larger than their limiting load, which leads to support collapse and eventually causes dynamic failure of the working face. The coal burst in working faces in horizontal sections of SICSs can be prevented by using deep-hole presplit blasting in a hard roof, destress blasting in coal masses, and support optimisation of working faces, showing a favourable preventative effect.
Highlights
Inclined coal seams are found in many coal producing areas, such as Xinjiang, Ningxia, Shanxi, Guizhou, Chongqing, Huainan, Gansu, and Beijing [1, 2]
To prevent coal bursts in LW5521-20, based on the mechanism of coal bursts induced by dynamic and static loads and intensity weakening theory for coal bursts [26, 27], preventative measures can be viewed in three ways: (1) decreasing the strengths of static stresses on coal masses in working faces and dynamic stresses induced by microseismic events; (2) weakening the intensity of areas influenced by coal bursts; and (3) optimising supporting parameters in working faces
Elastic energies Ee accumulated in hanging roofs are such that Ee ∝ L5h [8] while about 0.1% to 1% of Ee is transformed into microseismic energy Ed0 [29], which means that the longer the length Lh of hanging roofs, the greater the elastic energies Ee accumulated in the roof and the greater the microseismic energy Ed0 released during roof breaking
Summary
Inclined coal seams are found in many coal producing areas, such as Xinjiang, Ningxia, Shanxi, Guizhou, Chongqing, Huainan, Gansu, and Beijing [1, 2]. In terms of dynamic disasters in SICSs, Ju and Li [8] established a mechanical model for a fractured cantilever beam of main roof in SICSs along the inclination direction, and the expression for calculating energies in the cantilever beam was deduced. On this basis, the deep-hole presplit blasting technology for preventing coal bursts was proposed. All of these factors significantly influenced the safe production of the coal mine
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