Water inrush disasters are extremely prone to occur if the coal seam floor contains a confined aquifer. To find out the failure behavior of coal seam floor of paste filling working face, a beam-based theoretical model for the floor aquifuge was built, and then, the water inrush risk was evaluated based on the thickness of floor aquifuge. Next, the floor failure characteristics of the paste filling face was numerically studied and the effects of the filling interval and long-term strength of the filling body on the floor failure depth, stress and displacement distributions, and plastic zone were explored. The results showed that the theoretical model for evaluating the safety of the floor of the paste filling face based on the empty roof distance is proved to be consistent with that of the empirical formula judged based on the assumption that the paste filling working face was regarded as a cut hole with a certain width. The filling interval has a significant effect on the stress concentration of the surrounding rock, failure depth of floor, and roof-floor convergence. The smaller the filling interval is, the smaller their values are. When the filling rate is 98%, the long-term strength of the filling body is 5 MPa, and the floor failure depth is not more than 4 m. In contrast, the strength of the filling body has no obvious influence on the floor failure depth, but it has a certain impact on the roof-floor convergence. From the perspective of reducing floor failure depth, there is no need to increase the long-term strength of backfill, but it is necessary to increase the early strength of backfill so as to reduce the width of the equivalent roadway.
In order to study the space–time evolution law and the induced impact mechanism of overburden breaking in the tangential horizontal sublevel during the fully mechanized mining of extra-thick and steep coal seams, we took the Yaojie No. 3 mine as an example. Through the establishment of an overburden breaking mechanical model, the structural characteristics of hinged rock beams after overburden breaking and the space–time evolution law of overburden structure instability were analyzed, the static and dynamic load conditions that induce rockbursts were analyzed, and the induced impact mechanism of dynamic and static load superposition was revealed. Our research showed that, due to the asymmetry of the roof and floor, the coal body in the working face is in the strong shear stress zone at the end of the air inlet roadway, which easily produces shear failure. The lateral support pressure and the shear stress of the coal body in the goaf are the static load sources of the rockburst in the steep coal seam; after the roof overburden is broken, a hinge-bearing structure is formed under the support of the sliding force of the fault block and the floating gangue in the goaf. When the coal is mined in the lower section, the strong dynamic load formed by the impact of the fault block on the topmost coal is the main dynamic load source of the impact on the working face. Under the superpositions of the dynamic load and static load, the coal and rock lose stability and release energy in a large range, generating dynamic and static superimposed rockbursts. Furthermore, the internal mechanism of the occurrence of rockbursts during the mining of steep and extra-thick coal seams in the Yaojie No. 3 coal mine was revealed. The static load of the coal body comes from the clamping actions of the roof and floor, and the dynamic impact load comes from the clamping structure’s instability. The reason for the occurrence of rockbursts in the mining of steep and extra-thick coal seams in the Yaojie No. 3 coal mine was reasonably explained.
In this paper, through a similar simulation experiment, the roof rock breaking situation of horizontal sublevel caving method in extremely thick and steep inclined coal seam is studied, and the response characteristics of coal and rock mass under different dynamic load strength are analyzed. The mechanical response mechanisms of different mining positions under the influence of dynamic load and the law characteristics of the surrounding rock from elastic deformation to impact failure are revealed. The study shows that with the increase in the horizontal sublevel mining depth, the roof is gradually broken from the suspended state, and the broken block fills the goaf. The thin rock strata form a granular structure, and the thick rock strata form a block splicing and occlusion structure. On the same side of the coal seam floor, the concentrated stress gradually increases, and the closer the distance from the goaf is, the more obvious the stress change in the coal body below is. With the increase in dynamic load energy, the dynamic instability and failure of the dynamic load side of the roadway occur, and the stress of the bottom coal in the intake roadway of the working face increases due to the influence of the lateral abutment pressure of the goaf, while the stress of the bottom coal in the middle of the working face and the return airway decreases due to the mining of the upper section, which reveals that the dynamic load-induced dynamic behavior requires the critical energy. Due to vibration waves, the dynamic load effect is short, and the reflective stretching is generated on the surface of the roadway, resulting in the failure of the roadway. The peak acceleration increases linearly with the increase in source energy, indicating that the stronger the dynamic load energy is, the higher the impact risk is. When the dynamic load intensity is constant, the peak acceleration decreases with the increase in propagation distance, indicating that the vibration wave has the dominant propagation direction, and there are certain directional differences in the effect of coal and rock. When the dynamic load is applied, the impact failure of the coal body has a critical displacement. When the displacement of the roadway surface is less than this critical displacement, the impact failure will not occur.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.