Abstract:As one of the most common disasters in deep mine roadway, floor heave has caused serious obstacles to mine transportation and normal production activities. The third section winch roadway in the third mining area of Qitaihe Longhu coal mine has a serious floor heave due to the large buried depths of the roadway and the semicoal rock roadway, and the maximum floor heave is 750 mm. For the problem of floor stability, this paper establishes a mechanical model to analyze the stability of roadway floor heave by ana… Show more
“…However, numerous scholars have found that this effective stress fails to respond to changes in the pore structure within the fractured body [ 36 , 37 ]. Therefore, a correction for Terzaghi’s equation is needed in rock percolation scenarios; Biot [ 38 , 39 ] et al proposed an effective stress equation that considers the effect of the pore structure of the rock body: where α is the Biot coefficient (this is interchangeable with porosity ϕ).…”
Water infiltration in boreholes is a common problem in mine gas pre-extraction, where water infiltration can significantly reduce the efficiency of gas extraction and curtail the life cycle of the borehole. It is important to evaluate the effect of groundwater on the permeability of the coal body around a gas extraction borehole. In order to determine the seepage parameters of the fractured coal body system around the borehole, a water–gas two-phase seepage test was designed to determine the relative seepage parameters of the fractured coal media seepage system. The main conclusion is that the relative permeability of gas can be effectively increased by increasing the negative extraction pressure at the early stage of extraction to accelerate drainage to reduce the water saturation of the coal seam. Under the combined effect of porosity and seepage pressure, the relative permeability of gas and water in the fractured coal rock body shows three stages. The dependence of the total permeability on the effective stress is closely related to the stages in the evolution of the pore structure, and the total effective permeability decreases with the increase in the effective stress. A decrease in porosity can lead to a decrease in permeability and an increase in the non-Darcy factor. Through an in-depth analysis of the damage and permeability pattern of the coal body around the perimeter of the dipping borehole, the efficient and safe extraction of gas from dipping boreholes in water-rich mines is thus ensured.
“…However, numerous scholars have found that this effective stress fails to respond to changes in the pore structure within the fractured body [ 36 , 37 ]. Therefore, a correction for Terzaghi’s equation is needed in rock percolation scenarios; Biot [ 38 , 39 ] et al proposed an effective stress equation that considers the effect of the pore structure of the rock body: where α is the Biot coefficient (this is interchangeable with porosity ϕ).…”
Water infiltration in boreholes is a common problem in mine gas pre-extraction, where water infiltration can significantly reduce the efficiency of gas extraction and curtail the life cycle of the borehole. It is important to evaluate the effect of groundwater on the permeability of the coal body around a gas extraction borehole. In order to determine the seepage parameters of the fractured coal body system around the borehole, a water–gas two-phase seepage test was designed to determine the relative seepage parameters of the fractured coal media seepage system. The main conclusion is that the relative permeability of gas can be effectively increased by increasing the negative extraction pressure at the early stage of extraction to accelerate drainage to reduce the water saturation of the coal seam. Under the combined effect of porosity and seepage pressure, the relative permeability of gas and water in the fractured coal rock body shows three stages. The dependence of the total permeability on the effective stress is closely related to the stages in the evolution of the pore structure, and the total effective permeability decreases with the increase in the effective stress. A decrease in porosity can lead to a decrease in permeability and an increase in the non-Darcy factor. Through an in-depth analysis of the damage and permeability pattern of the coal body around the perimeter of the dipping borehole, the efficient and safe extraction of gas from dipping boreholes in water-rich mines is thus ensured.
“…CBM is gradually formed in the long-term complex geological evolution process (Wang and Du, 2020;Zhou et al, 2021), so its occurrence is affected by structural evolution, depositional environment, buried depth, roof and floor lithology, coal seam thickness, hydrogeology, and magmatic activity (Xie et al, 2018;Zou et al, 2018a;Zhang C. L. et al, 2020;Kong B. et al, 2021;Zhang C. L. et al, 2021). Tectonic evolution is the key factor controlling the generation, migration, and occurrence of CBM (Zou et al, 2018b;Zhang K. Z. et al, 2020;Zhou et al, 2022).…”
Geological structures of Sima coal mine in Shanxi Province were analyzed to understand the control effect of the geological structures on the occurrence of coalbed methane (CBM) in coal seam #3 of Sima coal mine. The CBM contents in the districts #2 and #3 of Sima coal mine were tested, and the effects of buried depth, fault and collapse column on the distribution of coalbed methane content are studied. The research results showed that: 1) The average content of CBM has a linear relationship with buried depth and overburden thickness, but in the smallscale range of buried depth, the dispersion between CBM and buried depth is very large. 2) Faults and collapse columns significantly affect the content of local CBM nearby, but from the largescale range such as the whole mining area, the average value of CBM content at a certain buried depth will not be affected by faults and collapse columns. 3) In the hanging wall of F29 normal fault, it is roughly estimated that the average escape rate of CBM near the fault is 13.9%, while in the footwall of F29 normal fault, this value is 0.7%–1.1%. The results show that there is a significant difference in the influence of the fault on the CBM content in the hanging wall and footwall. 4) The control effect of collapse column on CBM occurrence is related to the development height of collapse column, the cementation degree of collapse column, groundwater runoff conditions and other factors. It can be divided into three categories: aggregation action, escape action (such as collapse column X8) and no obvious effect (such as collapse column DX7).
“…Similarly, China has made many top coal mining research achievements. Other researchers have also studied in this field in different ways (S Bai and H Tu, 2020;Zhou et al, 2022;Zhang et al, 2020;Zhang and Zhang, 2019;Xie and Zhou, 2008) . In general, the research and application of thick coal seam mining technology in China is at the world's leading level.…”
Top coal caving has become one of the main mining methods for thick and extrathick coal seams. Because of coal seam conditions, the top coal thickness is not constant. It is necessary to study the influence of top coal thickness changes on the top-coal-caving mining process. To explore the migration law of top coal failure, the experimental means of similar simulation experiment, numerical simulation experiment and field monitoring data were used. Through a similar simulation test of three different top coal thicknesses, the change rule of top coal migration was analyzed. Moreover, the stress and displacement changes of a 14 m coal seam over a thick top coal caving face were monitored and analyzed comprehensively with the simulation results. The results show that when the top coal thickness is unchanged, the top coal vertical displacement in the upper part is larger than that in the middle part due to the top plate rotation in front of the working face, and the stress change follows an opposite trend. The simulation results were the same as the field test results. When the top coal thickness is changed, whether it is upper top coal or middle top coal, the top coal displacement and stress changes will increase. The top coal migration will be more obvious, and thus the crushing will be more serious.
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