Search Results (6)

The extensive adoption of large mining height technology and the progressive deepening of mining operations have presented formidable challenges to the safety of roadway support. The selection of roadway support configurations and their operational parameters is critically important in underground mining operations. Taking the open cut of Hongliu Coal Mine as the engineering background, this study conducts similar model experiments and field monitoring to evaluate the large-section open-cut support system. We aim to address unreasonable parameters and the low efficiency of this system in fully mechanized mining faces with large mining heights. The results demonstrate that deformation and failure initially occur at the cut corners. According to field observation data, the convergence of the system’s two sides across the three measuring stations is markedly greater than the roof subsidence on average (104.9 mm vs. 46.0 mm). This indicates the collapse of surrounding rocks on both sides. The peak abutment pressure of the cutting hole occurs approximately 16 cm from the coal wall (scaled to 3.2 m on site). Full article

Shallow-buried, hard, and extra-thick coal seams are very common in Xinjiang, China, but there are relatively few studies on the mine pressure law and the development characteristics of water-flowing fracture zones (WFFZs) during the mining of such coal seams. In this paper, the mine pressure of the top coal caving face in a shallow, hard coal seam with a hard roof and full bedrock (SHCSHRFB) is analysed, the laws of the surrounding rock deformation and stress of the open-off cut and roadway in the large-mining-height top coal caving face are studied, the characteristics of roof-breaking and overburden fracture development are analysed using the physical similarity simulation method, supporting suggestions for roadways are put forward, and three development stages of the WFFZ are analysed. Field monitoring shows that the hydraulic support stress in SHCSHRFB is weak, but the coal wall and roadway stability are good, which is significantly different from the results in the typical shallow-buried thin bedrock working faces. The measured height of the WFFZ is close to the physical similarity simulation results, but quite different from those arising from use of the empirical formula. Full article

The occurrence of surface strata movement in underground coal mining leads to the generation of numerous ground fissures, which not only damage the ecological environment but also disrupt building facilities, lead to airflow and easily trigger coal spontaneous combustion, induce geological disasters, posing a serious threat to people’s lives, property, and mining production. Therefore, it is particularly important to quickly and accurately obtain the information of ground fissures and then study their distribution patterns and the law of spatial-temporal evolution. The traditional field investigation methods for identifying fissures have low efficiency. The rapid development of UAVs has brought an opportunity to address this issue. However, it also poses new questions, such as how to interpret numerous fissures and the distribution law of fissures with underground mining. Taking a mine in the Shenfu coalfield on the semi-desert aeolian sand surface as the research area, this paper studies the fissure recognition from UAV images by deep learning, fissure development law, as well as the mutual feed of surface condition corresponding to the under-ground mining progress. The results show that the DRs-UNet deep learning method can identify more than 85% of the fissures; however, due to the influence of seasonal vegetation changes and different fissure development stages, the continuity and integrity of fissure recognition methods need to be improved. Four fissure distribution patterns were found. In open-cut areas, arc-shaped fissures are frequently observed, displaying significant dimensions in terms of depth, length, and width. Within subsidence basins, central collapse areas exhibit fissures that form perpendicular to the direction of the working face. Along roadways, parallel or oblique fissures tend to develop at specific angles. In regions characterized by weak roof strata and depressed basins, abnormal reverse-“C”-shaped fissures emerge along the mining direction. The research results comprehensively demonstrate the process of automatically identifying ground fissures from UAV images as well as the spatial distribution patterns of fissures, which can provide technical support for the prediction of ground fissures, monitoring of geological hazards in mining areas, control of land environmental damage, and land ecological restoration. In the future, it is suggested that this method be applied to different mining areas and geotechnical contexts to enhance its applicability and effectiveness. Full article

In order to effectively control the stability of surrounding rock in ultra-large span open-off cuts by employing the techniques of support strength theory calculations and analogical application methods, two sets of rational support schemes were proposed, and the optimal design of active support parameters in thick coal seams with ultra-large span open-off cuts was explored by using theoretical analysis, numerical simulation, and field experiments. The results demonstrated that the span is one of the key factors influencing the stability of the roadway roof, exhibiting an inverse quadratic relationship with the peak stress borne by the roadway roof. By utilizing the pre-stressing force of anchor cables and support strength formulas, two sets of active support schemes for controlling the surrounding rock in thick coal seams with ultra-large span open-off cuts were established, and an optimized support scheme was obtained through numerical simulation. These findings provide references and guidance for related mining engineering under actual conditions in mines. Full article

Close-distance multilayer coal mining is common. Under the condition of extremely close-distance coal seams, it is extremely difficult to control the surrounding rock of large-span open-off cut roadways in multistress concentration areas. Based on the engineering background of the 23616 open-off cut roadway in Chaili Coal Mine, this paper investigated the influence of upper close seam mining on the stress and deformation of the lower large-span roadway in detail. The control effect of a high-strength prestressed yielding bolt and cable was analyzed systematically. The support system stress was coordinated by the yielding member to avoid excessive stress on the local support structure and reduce the stress concentration of the surrounding rock. Before and after the upper coal mining, the stress changed mainly on the left and right sides, and the displacement changed mainly on the right side and roof. The maximum deformation of the roof and the right side and the left side at two engineering observation sections was 85 mm, 61 mm, 48 mm and 68 mm, 53 mm, 46 mm, respectively. The surrounding rock control effect was relatively ideal, which can meet the needs of roadway installation support. Full article

Hard and thick magmatic rocks are widely distributed in many mining areas in China. Their fracture migration could cause mechanical effects such as the evolution of overburden structure, the sudden change of surface subsidence, and the transformation of accumulated elastic properties, inducing strong dynamic phenomena and even coupled geo dynamic disasters. In this study, by means of theoretical analysis and similar material simulation testing, the fracture of hard thick magmatic rock and the fracture development characteristics of stope are analyzed, and the following research results are obtained: (1) the mechanical model of an elastic foundation beam is established, and it is found that the bending moment in the middle of hard thick magmatic rock is greater than the bending moment at the end, and the magmatic rock first produces fractures in the middle, and then the initial fracture occurs. (2) The existence of hard thick magmatic rock blocks the development of fractures in the longitudinal direction. The bed separation and fracture undergo three processes of generation, development and closure. When the working face advances 160 m, 200 m and 270 m, the maximum bed separation shape on the strike section experiences triangle trapezoid crescent shape. (3) A ladder type fissure channel is formed above the working face side and the open cut hole side. When the working face is advanced 160 m, the ladder type fissure channel develops to the bottom of the hard thick rock layer, providing a ladder type channel for gas flow. After the hard thick rock layer is broken, a large number of elastic properties are released, which produces a strong impact force on the gas rich area of the bed separation, and also causes a sharp rise in the gas pressure of the bed separation at the bottom of the magmatic rock. A large amount of high-pressure gas in the bed separation space flows reversely to the working face along the ladder type gas channel, which can easily induce a gas outburst, coal and gas outburst or other disasters. (4) The correctness of the similar simulation experiment is verified by the field data. Technical measures for preventing gas outbursts in bed separation by surface drilling and pressure relief gas extraction are put forward. The research results have a certain guiding role for the prevention and control of dynamic disasters and the design of roadway support under the condition of a hard and thick key stratum overlying the working face. Full article