Development of overlying strata collapse and water-conducting fractured zone in shallow coal seams mining
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摘要:
浅埋煤层群井下开采对上覆岩层有较大影响，不仅会加剧地表沉陷，而且可能造成地表和地下水流失，影响生态环境和发展安全。为进一步掌握浅埋煤层群开采过程中覆岩垮落规律和裂隙分布特征，以宁夏石嘴山二矿2#、3#、5#和6#煤层为研究对象，分别采用相似材料模拟试验、数值模拟和经验公式计算，分析导水裂隙带发育规律；同时采用相似材料模拟试验方法，分析一次采动和多次采动覆岩垮落规律。研究结果表明：（1）浅埋近距离煤层群开采时，上层煤周期来压步距大于下层；（2）单层煤开采时，上覆岩层垮落以“铰接结构”和“台阶结构”形式出现，两层及多层煤开采时，“铰接结构”稳定性明显降低，垮落结构主要以“台阶结构”稳定在采空区上方；（3）一次采动时形成“梯形”裂隙区，二次采动时形成“M”形裂隙区，多次采动时形成两个“等腰梯形”裂隙区；（4）导水裂隙带发育高度一次采动时呈平稳增长—缓慢变化趋势，重复采动时，导水裂隙带发育高度则呈快速增长—平稳增长趋势；（5）相似材料模拟试验值及数值模拟结果与实测值较为接近，且均符合煤矿防治水规定。该结果可为类似矿区煤层群高效开采提供参考依据。
Abstract:Shallow underground mining of coal seams has significant impacts on the overlying rock formations, not only exacerbating surface subsidence but also potentially leading to surface and groundwater loss, thereby affecting the development and safety of the ecological environment. To further understand the collapse law and fracture distribution characteristics of overlying strata during the shallow coal seam mining process, a study was conducted on the 2#, 3#, 5#, and 6# coal seams of the Shizuishan No. 2 Mine in Ningxia. Similar material simulation tests, numerical simulations, and empirical formula calculations were employed to analyze the development of water-bearing fracture zones and the collapse characteristic of the overlying strata under single and multiple mining operations. The results indicate that: (1) During the mining of shallow and closely spaced coal seams, the gob-side entry retention time of the upper coal seam is greater than that of the lower coal seam. (2) When mining a single coal seam, the collapse of the overlying strata occurs in the form of “hinged structure” and “step structure”. As to the mining of two or more coal seams, the stability of the “hinged structure” decreases significantly and the collapse structure mainly stabilizes as a “step structure” above the goaf. (3) During the initial mining, a “trapezoidal” fracture zone is formed, while during the secondary mining, an “M-shaped” fracture zone is formed, and during multiple mining operations, two “isosceles trapezoidal” fracture zones are formed. (4) The development height of the water-bearing fracture zone shows a steady increase or slow change during the initial mining. While during repetitive mining, the development height of the water-bearing fracture zone shows a rapid increase to steady growth. (5) The values obtained from the similar material simulation tests and numerical simulations are similar to the measured values, and all of them comply with the regulations for coal mine water control. These results can provide a basis for the efficient mining of coal seam groups in similar mining areas.
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表 1 模型厚度及岩石力学参数
Table 1. Model thickness and rock mechanics parameters
岩性 模型厚度/cm 累计厚度/cm 密度/（kg·m−3） 体积模量/MPa 剪切模量/MPa 抗拉强度/MPa 黏聚力/MPa 内摩擦角/（°） 泊松比 砂岩 31.45 31.45 2 400 45 000 6 000 5.65 35.0 45 0.30 2#煤 4.22 35.67 1 900 2 000 200 1.11 3.0 25 0.35 砂岩 3.16 38.83 2 400 45 000 6 000 5.65 35.0 45 0.30 3#煤 7.38 46.21 1 900 2 000 200 1.11 3.0 25 0.35 砂质页岩 15.83 62.04 2 100 30 000 4 000 3.64 17.0 30 0.30 页岩 12.78 74.82 2 380 69 700 4 650 3.20 3.1 40 0.40 砂岩 7.23 82.05 2 400 45 000 6 000 5.65 35.0 45 0.30 砂质页岩 4.13 86.18 2 100 30 000 4 000 3.64 17.0 30 0.30 砂岩 4.13 90.31 2 400 45 000 6 000 5.65 35.0 45 0.30 砂质页岩 20.66 110.97 2 100 30 000 4 000 3.64 17.0 30 0.30 灰岩 4.13 115.10 2 700 15 700 2 830 8.42 40.0 40 0.23 砂岩 6.20 121.30 2 400 45 000 6 000 5.65 35.0 45 0.30 砂质页岩 7.23 128.53 2 100 30 000 4 000 3.64 17.0 30 0.30 砂岩 8.26 136.79 2 400 45 000 6 000 5.65 35.0 45 0.30 砂质页岩 3.10 139.89 2 100 30 000 4 000 3.64 17.0 30 0.30 5#煤 2.07 141.96 1 900 2 000 200 1.11 3.0 25 0.35 砂岩 2.07 144.03 2 400 45 000 6 000 5.65 35.0 45 0.30 砂质页岩 2.58 146.61 2 100 30 000 4 000 3.64 17.0 30 0.30 6#煤 11.36 157.97 1 900 2 000 200 1.11 3.0 25 0.35 砂岩 7.23 165.20 2 400 45 000 6 000 5.65 35.0 45 0.30 7#煤 1.55 166.75 1 900 2 000 200 1.11 3.0 25 0.35 砂岩 3.61 170.36 2 400 45 000 6 000 5.65 35.0 45 0.30 灰岩 3.10 173.46 2 700 15 700 2 830 8.42 40.0 40 0.23 
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表 2 岩层材料配比表
Table 2. Rock layer material ratios
岩层名称 累计厚度/cm 配比号 河砂/kg 石膏/kg 大白粉/kg 砂岩 73.34 728 492.8 42.24 168.98 煤 26.58 928 229.7 15.31 61.24 砂质页岩 53.53 864 411.1 92.5 61.67 页岩 12.78 737 85.88 11.04 25.76 灰岩 7.23 628 41.64 4.16 16.66
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表 3 2#煤层回采来压步距
Table 3. Pressure step of 2# coal seam mining
来压次数 推进距离/m 来压步距/m 来压次数 推进距离/m 来压步距/m 初次来压 53 18 5 155 24 1 71 18 6 177 22 2 89 18 7 201 24 3 109 20 8 219 18 4 131 22 9 240 21
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表 4 3#煤层回采来压步距
Table 4. Pressure step of 3# coal seam mining
来压次数 推进距离/m 来压步距/m 来压次数 推进距离/m 来压步距/m 初次来压 31 31 11 131 6 1 45 14 12 143 12 2 53 8 13 151 8 3 61 8 14 163 12 4 67 6 15 169 6 5 74 7 16 189 20 6 87 13 17 195 6 7 93 6 18 203 8 8 109 16 19 210 7 9 115 6 20 217 7 10 125 10
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表 5 5#煤层回采来压步距
Table 5. Pressure step of 5# coal seam mining
来压次数 推进距离/m 来压步距/m 来压次数 推进距离/m 来压步距/m 初次来压 56 24 5 182 26 1 80 24 6 206 24 2 104 24 7 224 18 3 130 26 8 240 16 4 156 26
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表 6 6#煤层回采来压步距
Table 6. Pressure step of 6# coal seam mining
来压次数 推进距离/m 来压步距/m 来压次数 推进距离/m 来压步距/m 初次来压 28 28 8 132 12 1 38 10 9 148 16 2 56 18 10 159 11 3 74 18 11 168 9 4 86 12 12 174 6 5 98 12 13 200 26 6 112 14 14 210 10 7 120 8 15 220 10
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表 7 不同方法导水裂隙带发育高度对比表
Table 7. Comparison of development height of water-conducting fracture zone in different methods
取值类型 2#煤导水裂隙带发育高度/m 5#煤导水裂隙带发育高度/m 误差/% 6#煤导水裂隙带发育高度/m 误差/% 实测值 31.45 35.00 0 104.00 0 相似材料模拟试验值 31.45 33.42 4.5 93.12 10.4 数值模拟值 31.45 25.20 28.0 95.62 8.0 经验公式值 36.14～62.66 16.41～39.39 90.97～117.49
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