Joint response of surface subsidence and strong mine earthquake under thick, high-hardness strata in a deep coal mine

An overview of the face of the business

Yingpanhao coal mine is located in Wushen Banner, southwest of Ordos City, Inner Mongolia Autonomous Region. The mine is divided into four mining areas: 21 mining areas, 22 mining areas, 23 mining areas, and 24 mining areas. Mining Area 22 is the first mining area of ​​the mine. It is located in the northern part of the industrial site of Yingbanhao Coal Mine. It is 2.65 km long from north to south and 13.6 km wide from east to west, covering an area of ​​17.24 km2. The ground elevation in mining area 22 ranges from +1244.6 m to +1261.4 m, and the mineable coal seams in the area are coal seams 2–2 and 3−1, with bottom elevations ranging from +490 m to +540 m and +450 m to + 500m straight.

Mining Area 22 is the primary mining area of ​​the 2-2 coal seam, and is currently the primary mining area of ​​the 2-2 coal seam. The bottom elevation of the coal seam ranges from +490 m to +540 m, with an average burial depth of 722.88 m. The thickness of the coal layer ranges from 3.16 m to 10.24 m, with an average thickness of 6.29 m. The coal consists mostly of dark coal, followed by bright coal, with semi-anthracite as the main type. The coal joint has a Mohs hardness of f = 1.36, and the mining method used is full mining using an all-inclusive mining approach. Currently, there are six working faces arranged in mining area 22, with the mining sequence as follows: 2201 working face → 2202 working face → 2203 working face → 2204 working face → 2205 working face → 2206 working face. Among them, working faces 2201 and 2202 have completed mining operations, and working faces 2303 have not completed mining operations. The layout of the work faces is shown in Figure 1. The work face 2201 serves as the primary mining face. This study focuses primarily on working faces 2201 and 2202, both of which have a pitch length of 300 m and a strike length of 2709 m.

Figure 1

Layout of working faces and surface movement monitoring stations in mining area 22 of Yingpanhao coal mine.

Geological conditions of the layers

The stratigraphic structure of mining area 22 in Yingpanhao coal mine consists of the Quaternary system, Cretaceous system, and Jurassic system formations from top to bottom. Coal seam 2-2 is located in the Lower Jurassic Yan'an Formation. Figure 2 shows the rock column of the K7-7 well in Mining Area 22. Specifically, the thickness of the Quaternary system ranges from 58.9 to 96.6 m, with an average of 82.6 m, and is composed mostly of brownish-yellow. Yellow-gray siltstone and fine sandstone. The thickness of the Lower Cretaceous Zidan Group ranges from 286.9 to 374.6 metres, with an average of 337.3 metres, and is mainly composed of medium reddish-brown and purplish-red sandstone and fine sandstone. The thickness of the Middle Jurassic Ziliujing Formation ranges from 132 to 195.83 m, with an average of 166 m, and is mainly composed of coarse-grained sandstone. The Lower Jurassic Yan'an Formation is mainly composed of medium-coarse-grained, gray-green sandstone and conglomerate coarse-grained sandstone, interbedded with fine-grained sandstone and sandy mudstone.

Figure 2

Vertical diagram of well K7-7 in mining area 22.

Figure 2 depicts the vertical diagram of the K7-7 well in the working face 2202. According to the main layer theory 25,29, it was calculated that there are five main layers above the surface of the working face 2202.

Main Layer 1: Fine sandstone, located 51 m above a 34 m thick coal layer.

The second main layer: medium-grained sandstone located at an altitude of 175 m above the 37 m thick coal layer.

Main Layer 3: Fine sandstone, located at 241 m above a 30 m thick coal layer.

Main Layer 4: Mainly composed of fine and medium-grained sandstone, it lies at 334 meters above an 81-meter-thick coal layer.

Main Layer 5: Mainly composed of medium-grained and fine-grained sandstone, it lies at an elevation of 544 meters above an 84-meter-thick coal layer.

Within the Cretaceous system, two main groups of major strata are identified, namely major strata 4 and 5. These layers are characterized by great thickness, high strength, general safety, and a great distance from the coal layer. The physical and mechanical properties of overburdened rocks in mining area 22, along with the results of major stratigraphy identification, are summarized in Table 1. These data have been measured directly on site by coal mine personnel and are accurate and reliable. .

According to the theory of layer movement in mines, during the coal mining process, as the mining area expands, the overlying layers of the hollow continuously collapse, and the layer separation fractures gradually propagate upward, and finally end up at the bottom of the upper layer. Apply thick solid layers30. With the continuous expansion of the mining area, the area above the separation layer gradually increases, and the thick hard layers become increasingly exposed. When it reaches the collapse limit, the fracture of the thick hard layers will affect the movement of the overlying layers in the mining area, and may even lead to large surface subsidence and high-energy earthquake events in the mine, posing a safety threat. And efficient production of the mine. It can be concluded that for the 22nd mining area of ​​Yingpanhao coal mine, the fracture movement of Jurassic and Cretaceous sandstone will have a great impact on the safe and efficient mining of the lower coal seams, making targeted research necessary and urgent.

Table 1: Physical and mechanical parameters of the overlying layers and results of identification of the main layers in mining area 22.

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