Rockburst is globally regarded as one of the most severe and complicated mining dynamic disasters to predict or control. Generally, the occurrence mechanism of rockbursts can be considered as a process of the elastic strain energy accumulation, emancipation, transmission, and occurrence. Tracing to the source, the reasons for large accumulation of elastic strain energy in coal and rock mass are the high stress of the roof layer that loads on the coal and rock masses around the mining space coupling effect with the natural horizontal tectonic stress. In this study, using the minimum energy theory and elasticity theory, the analytical formula for calculating elastic strain energy of the roof cantilever beam structure acting on the coal body load in front of the working face is deduced. Accordingly, we achieved a method of using hydraulic fracturing to improve the roof structure. In detail, we use a high-pressure jet to cut the cantilever roof structure, which can make a prelocated fracture surface, and then utilize the packers to make sure that the injected high-pressure fracturing fluid is propagating along the prelocated fracture surface and can cut off the cantilever roof structure eventually to prevent rockbursts in advance. Due to the rockburst occurrence mechanism and the quantitatively elastic strain energy analytical formula, a preconditioning water jet cutting induced fracture surface to create orientation-controllable hydraulic fracture strategy is proposed to guard against the high hazard caused by the massive elastic strain energy, which accumulated in the coal body in front of the working face and coal pillar.
In view of the serious problem of bottom-drum damage in deep mining along empty roadways, the asymmetric bottom-drum damage characteristics and control mechanisms of deep mining along an empty roadway were studied using the trackway of the 11060 working face in Zhao Gu II mine as the research background. Based on the slip-line theory, support-pressure distribution law, and Griffith’s damage-criterion theory, the mechanism of asymmetric bottom drums and the maximum fracture-development depth of the bottom plate in a deep roadway under top-plate fracture perturbation were analyzed. The 3DEC discrete-element software was used to simulate and analyze the characteristics and evolution of the asymmetric bottom bulge of the roadway under dynamic-load disturbance, and the asymmetric control scheme of “slurry anchor reinforcement + top cutting and pressure relief” was proposed. The results show that, under the influence of static load of deep high-abutment pressure and the dynamic-load impact of the instability of the masonry-beam structure under periodic pressure of the adjacent working face, the deep-mining goaf roadway was prone to producing asymmetric floor heave. The floor-heave degree and maximum fracture-development range of the roadway in the affected area under the influence of dynamic load > those in goaf roadway > those in the roadway in the stable area affected by tunneling. The distribution of stress, displacement, and maximum floor heave was skewed to the side of the coal pillar in the goaf, showing an inverted right oblique V shape. The asymmetric floor heave of a roadway can be effectively controlled by grouting anchor-cable reinforcement (increasing the anti-damage limit) and roof-cutting pressure relief (cutting off the dynamic-load source). The research results can provide an important reference for the control of roadway floors under similar geological conditions.
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