Aiming at the wide range of rock strata movement and collapse, poor stability and high damage rate of the working face support and being prone to crushing of the support in large mining height face, analog simulation, theoretical analysis, and field measurements have been carried out to analyze roof breaking structure form and calculation method of support reasonable support resistance of large mining height face. The researches show that, affected by the space of the mined-out area, the roof of the large mining height working face will take on the structural form of “combined suspended beam-nonhinged roof-hinged roof”; the interaction system between the support and the surrounding rock consists of “hinged roof structure,” “nonhingeable roof structure,” “combined suspension beam structure,” and the support. The support resistance should adapt to the change of the overlying rock structure’s instability movement, bearing the weight of the structure itself and the additional load generated by the movement. Combining with the mining conditions of Jinhuagong Coal Mine’s large mining height face in Datong mining area, the reasonable support resistance of the working face support is analyzed. The mine pressure monitoring shows that the ZZ13000/28/60 type support and shield hydraulic support can meet the requirements of roof control; the research results ensure the safe mining of the large mining height face.
In order to solve the problem of support crushing, rib spalling, and partial roof fall in working face crossing fault structure area, taking II1023 working face of Haizi Mine as the engineering background, the numerical simulation, theoretical analysis, and field measurement were used to simulate the rock activity law in the process of working face crossing fault. Based on this, the mechanical model of the interaction between the support and the surrounding rock in the fault area was established, and the calculation formula of the support strength required by the support under different equilibrium criteria was deduced, which provides a basis for the reasonable selection of hydraulic support. The results show that the rock stress of the working face passing through the fault zone is divided into high-stress section when it is gradually close to the fault and low-stress section after passing through the fault. In the high-stress section, the rock stress increases in front of the working face, and the distribution form is similar to the stress distribution of the narrow coal pillar. The roof easily forms a long hanging roof and slip along the fault surface, which is prone to rib spalling and partial roof fall and support crushing. The support strength is mainly related to fault dip angle, fault cohesion, support beam length, length of the main roof rock beam, and the distance between working face and fault. The reasonable support strength should be determined by the calculation results under different equilibrium criteria. When the working face advances in the high-stress section, the required support strength of the support increases with the increase of the fault dip angle and the length of the main roof rock beam and decreases with the increase of the fault cohesion, the length of support beam, and the distance between working face and fault. With the increase of the fault dip angle, the form of rotary instability changes and the probability increases. The field practice shows that during the fault crossing of the II1023 working face, the working resistance of the support shows the characteristics of high-pressure area and low-pressure area, but it does not exceed the rated working resistance of the selected support. The fully mechanized coal face passed through the fault area safely, and there were no accidents such as support crushing, rib spalling, and partial roof fall.
The extremely soft coal seam roadway has the problems of low surrounding rock strength and difficult support. Based on the engineering background of the mining roadway in the extremely soft coal seam of the Quandian coal mine, this paper adopts the research method combining numerical simulation and field measurement. The stress field, displacement field, support force, and loading arch structure characteristics of roadway surrounding rock under bolt-mesh-cable support and existing shed-cable support are compared, and the control principle of bolt-mesh-cable in extremely soft coal seam roadway is expounded. Our study indicated that compared with nonsupport and shed-cable support, the pressure stress range of the surrounding rock in extremely soft coal seam increases, and the stress gradient decreases when bolt-mesh-cable support is used. The roadway displacement and displacement difference decrease. The components of the support achieve stress coordination. The thickness of the loading arch formed in the surrounding rock is large, and the compressive stress in the arch is evenly distributed. The bolt-mesh-cable significantly improves the stress environment and the stability of the roadway. The field practice shows that the roadway deformation is small after the bolt-mesh-cable support is adopted, and the roadway section during excavation and mining meets the requirements of safety production.
In order to avoid the problem of repeated repair of roadways in the upper mining area of upward mining in the integrated mine, taking the roadways in the 302 mining area of Shancheng Coal Mine as the research object, the failure characteristics of overlying strata and the evolution characteristics of roadway plastic zone in the mining process of underlying coal seam were studied by combining theoretical analysis, numerical simulation, and engineering measurement. The influence law of underlying coal seam mining on the integrity of 3# coal seam and the stability of roadways in the 302 mining area was revealed, and the repair opportunity of roadways in the upper coal seam and the reasonable position of open-off cut in the lower coal seam working face were determined. The research shows that due to the influence of the mining of the working face in the underlying coal seam, the plastic failure of the overlying strata is serious during the upward mining of Shancheng Coal Mine, but there is no step dislocation, but the overall subsidence is presented. The plastic zone range of roadway in 302 mining area first increases and then tends to be stable with the mining of 97308 working face in underlying coal seam, and the roadway repair should be carried out after 280 m advance of 97308 working face. Based on the coordination between the influence of the cutting position of the underlying coal seam on the variation characteristics of the plastic zone of the upper roadway and the saving of coal resources, it is determined that the cutting position of the underlying 153308 working face is advanced to 340 m. The field engineering application shows that the deformation of roadway surrounding rock meets the production requirements by implementing the above mining parameters, and the rerepair of roadway surrounding rock deformation in 302 mining area of 3# coal seam is avoided.
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