Study on the Evolution Law of Overburden Breaking Angle under Repeated Mining and the Application of Roof Pressure Relief

Abstract

Aiming at the serious problems caused by coal mine mining activities causing the rock burst accidents, this paper is based on rock mechanics and material mechanics to establish the key layer breaking by the double-key layer beam breaking structural mechanics model of a single working face and double working face under repeated mining. The theoretical calculation formula of the angle was used as the theoretical basis for the elevation angle of the pre-reloading hole of the hard roof. The rationality and reliability of the formula were verified by the physical similarity simulation experiment and the 3 Dimension Distinct Element Code numerical simulation experiment, revealing the rock formation under the influence of repeated mining. The results show that the derived key layer breaking angle formula is suitable for the theoretical calculation of the breaking angle of the key layer of a single coal seam when the repeated disturbance coefficient is λ = 1; when it is λ = 2, it is suitable for the repeated mining of the short-distance double-coal mining. The rationality and reliability of the theoretical formula of the breaking angle of the double key layer of single coal seam and double coal seam were verified by the physical similarity simulation experiment. Through the 3DEC numerical simulation results and theoretical calculation results, the W1123 working face hard top pre-cracking pressure relief drilling elevation angle was 78°. The drilling peeping method was used to verify the results. The results show that the theoretical formula of the critical layer breaking angle is well applied in engineering practice.

Monitoring and correction of the stress in an anchor bolt based on Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis

“…Bolts are vital to the advancement of underground excavation in engineering work, such as subway tunnels and coal mines, as they connect broken rock mass, enhance the stability of underground coal mine roadways and surrounding rock, and reduce the occurrence of rock burst . In countries such as China where huge amount of coal is mined, problems of roof falling (roof collapse), land subsidence, and collapse result in a series of secondary disasters, directly threatening production, and life safety . Monitoring and evaluation of the anchoring performance is an important basis to judge the effectiveness of bolts, and hence, to ascertain the safety of the underground coal mine roadways.…”

A Modified Bursting Energy Index for Evaluating Coal Burst Proneness and Its Application in Ordos Coalfield, China

“…Parameters c ε and r ε are the strain at the peak point and ultimate failure point. From Equations (1) and (5), it can be found that both of the indexes et W and e K can determine energy accumulating and releasing ability of coal. For the index K e , which is defined as the ratio of accumulated strain energy density before the peak strength u a to the released strain energy density after peak strength u r , can be calculated with uniaxial compression test.…”

“…Parameters c ε and r ε are the strain at the peak point and ultimate failure point. From Equations (1) and (5), it can be found that both of the indexes et W and e K can determine energy accumulating and releasing ability of coal. Similarly, the parameters u a and u r can be expressed by following equations:…”

“…Therefore, the coal burst severely threatens personnel safety and may delay the project schedule in coal mine. Therefore, studies on the occurrence, predication, and control of coal burst events have great scientific and engineering significance [4,5].…”

Experimental Study on the Effect of Advancing Speed and Stoping Time on the Energy Release of Overburden in an Upward Mining Coal Working Face with a Hard Roof

“…We define the phenomenon of rock burst induced by the unilateral or comprehensive influence of the stope advancing speed and stopping time as the advancing speed-stoping time effect. In this paper, we deduce the theoretical calculation formula of the key stratum fracture angle and study the fracture situation of the key stratum of the overburden in the mining process of the working face [25]. Then, the method of combining microseismic monitoring technology with similar simulation experiments is used, and only the influence of the advancing speed-stoping time effect on the characteristics of microseismic events is considered, thus revealing the mechanism of rock burst induced by the advancing speed-stoping time effect of the working face.…”