93 / 2023-06-14 22:04:41

Mechanism and characteristics of rock burst induced by the layered fracture energy storage structures of the steeply inclined and extremely thick coal seams

Steeply inclined and extremely thick coal seams,roadway rock burst,layered fracture energy storage structures,disturbance stress,energy release

Taking the steeply inclined and extremely thick coal seams (SIETCS) with an average dip angle of 87° in China as the research background. It exhibits features such as immense coal seam thickness, steeply inclined distribution of coal and rock layers, and significant influence from high horizontal stress, which resulted in severe rock burst incidents. The features and mechanisms of rock burst occurrences in the SIETCS were investigated. Statistical analysis revealed that each rock burst in the SIETCS resulted in vertical displacement of the surrounding rock in the roadway or damage to support equipment. Borehole detection revealed that the primary range of fracture development in the vertical direction of the roadway is between 2.6~3.9m from the vertical boundaries, which is significantly greater than the range of fracture development in the horizontal direction of the roadway. The directions of fractures development were approximately parallel to the roadways' surface. Notably, the roadway's upper and lower boundary coals exhibited a distinct concentration of horizontal stress and energy, with the peak position approximately 3~4m away from the boundaries. Based on the calculations, it was discovered that the stability of the surrounding rock within the stress and energy concentration zones was inferior. In summary, these results indicate the presence of layered fracture energy storage structure（LFESS） within the upper and lower boundary coals of the roadway. These structures exist in the state of high static load and stores a considerable amount of elastic energy, making it prone to unstable failure. Consequently, the zone composed of multi-layered LFESS is referred to as the rock burst hazard zone（RBHZ）. The occurrence of rock bursts in RBHZ requires the satisfaction of stress and energy conditions. Under the influence of disturbance stress, the multi-layered LFESS undergoes simultaneous failure, releasing energy that converts into kinetic and dissipative energy. As a result, the impacted coal mass gains sufficient kinetic energy to be ejected towards the free space, leading to the deformation of the surrounding vertical rock in the roadway and damage to supporting equipment, which lead to the occurrence of rock burst disasters. Additionally, It was also found that LFESS may develop within the mined sections of the SIETCS, thereby forming additional coal seam RBHZ. Under the influence of initial disturbance stress, the coal seam RBHZ undergoes damage and releases energy, resulting in secondary disturbance stress. The secondary disturbance stress may trigger rock bursts in the roadway or increase the intensity of rock bursts, or expand the damage range of roadway caused by rock bursts.