Characteristics and Control of Mining Induced Fractures above Longwall Mines Using Backfilling

Abstract

Water conservation in mining is the key to solving the conflict between coal resource exploitation and ecological environment protection, especially in arid and semi-arid mining areas. Continuous excavation and continuous backfilling (CECB) in longwall mining is an important method to realize water conservation mining. Considering the different boundary conditions of the main roof stress in different mining phases, the mechanical models of clamped–clamped beam, continuous beam, and elastic foundation beam among filling body, main roof, and strata are established. Furthermore, the spatio-temporal evolution mechanisms of mining-induced fractures (MIF) are studied. It is found that there is a hyperbolic function relationship between MIF and the mining roadway (MR) filling percentages. Based on mining the XV coal seam under CECB in the Wangtaipu Coal Mine, the distribution patterns of MIF are studied. It is concluded that the distribution pattern is an isosceles trapezoid with the moving angle of overlying strata as the bottom angle, and the upper and lower boundary of MIF as the two parallel sides. Based on the influence coefficient of MR filling percentages on MIF, the curve of the MIF height is divided into three ranges, which include the stability control range, the critical range, and the lost control range. The controlling effects of MR filling percentages are studied, and the calculation expression of the MIF height in the stability control range is given. In engineering practice, 90% MR filling percentage is used for CECB. The MIF height is about 3.0 times of mining height, and the main roof beam is not broken. The water-resisting property of aquiclude III is not destroyed, thus, the mining does not adversely impact the water. The results provide theories and practices for controlling MIF under CECB in the conditions of extremely close distance aquifers.

Prediction and Maintenance of Water Resources Carrying Capacity in Mining Area—A Case Study in the Yu-Shen Mining Area

“…It can be seen that the water utilization rate of Yu-Shen mining area is 34.04% on average [63]. In addition, in light of the distribution of water resources per capita from 2014 to 2018 released by the National Bureau of Statistics [64], the water resources per capita of Yu-Shen mining area are 1000-2000 m 3 , revealing that it is a moderate water scarcity area. Based on the comprehensive evaluation value Φ of the WRCCMA of each borehole, the Kriging method was employed to draw the contour map of the Φ under longwall full-seam mining in the Yu-Shen mining area, as shown in Figure 12.…”

“…With the depletion of coal resources in central and eastern China, the focus of coal mining has gradually shifted to arid and semi-arid areas in Northwest China, where the proven reserves make up to more than two thirds of the country's total, and contributes to over one third of China's annual coal production [1,2]. However, Northwest China has a dry climate, sparse vegetation, and water resources are scarce, accounting for only 3.9% of the entire country [3]. Water resources are likely to be…”

Characteristics of Roof Ground Subsidence While Applying a Continuous Excavation Continuous Backfill Method in Longwall Mining

“…The dimension of the mining panel included a length of about 300 m, a width of about 160 m, an average thickness of the coal seam of 2.5 m, and an average bury depth of 220 m. There is no large geological tectonism, and the dip angle of the coal seam is 1~2 • , so the thickness of each stratum in the panel is assumed to be constant. According to the drilling data [27][28][29], the typical stratigraphic column in the mining area is shown in Figure 3. The direct roof of the coal seam was gray limestone which had a UCS value of 101.6 MPa and a BTS value of 4.0 MPa, which was categorized as a hard roof.…”

“…As seen in Figure 1, this proposed method plans transportation roadways in a panel as with the traditional longwall mining, while achieves the coal mining objective in the manner of roadway excavation. The excavation of one mining roadway (MR) in the CECB method is equal to one cut of a shearer in conventional longwall mining, and the length and width of the MR is equal to the length of the mining face and the distance a shearer penetrates to the coal seam, respectively [28,29]. This mining method has smaller exposure area on the roadway roof; moreover, it has the coal wall and the filling body to support two ribs of the roadway.…”

Cemented Backfilling Mining Technology for Gently Inclined Coal Seams Using a Continuous Mining and Continuous Backfilling Method

“…Zhao [23] used loess to replace fly ash in traditional paste-filling materials and studied the mechanical properties of paste-filling materials using different proportions, which provides a reference for backfill mining in the ecologically fragile areas of western China. Ma [24,25] studied the backfill method for filling nearly horizontal coal seams with high-water materials using the Wongawilli mining method, analyzed the evolution characteristics of overlying strata fractures, and achieved a waterpreserving approach to mining coal resources. Sun and Feng [26][27][28][29][30] analyzed the structure of high-water materials, developed ultrahigh-water material (97 vol%), and studied the control principle of overlying rock movement.…”