The stability of long trench section in sand cobble stratum of mine water cutoff curtain
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摘要:
露天煤矿长时间大流量疏排降水导致矿区地下水资源严重浪费、井田周围生态环境急剧退化、生产运行成本大幅增加，截水帷幕技术为露天矿山地下水控制提供了新的思路。槽段稳定性直接关系到截水帷幕施工安全、成槽效率及防渗效果。为探讨矿山截水帷幕砂卵石地层在成槽时长幅槽段的稳定性，以我国内蒙古东部某露天煤矿为例，采用二维和三维水平条分法对砂卵石地层长幅槽段稳定性影响因素及规律进行研究，并对比分析二维与三维水平条分法在安全系数计算结果上的差异；借助FLAC3D软件模拟分析砂卵石地层分别开挖17.5、22.5 m 2种长度时槽段的稳定性；结合上述分析结果给出砂卵石地层长幅槽段稳定性控制措施；再通过超声波测试手段验证长幅槽段稳定性及控制效果。研究结果表明：影响槽段稳定性的主要因素有地层岩土体性质、槽段开挖深度、泥浆液面、泥浆密度、泥浆液面与地下水位高差及单幅槽段长度；调整泥浆参数、提高泥浆液面、降低地下水位、优化成槽次序及控制成槽时间等措施可以增加长幅槽段的稳定性；该地层条件下单幅槽段长度不超过21 m时，槽段可以保持直立稳定，长幅成槽技术可行。
Abstract:Long-term high flow rate drainage of precipitation in open-pit coal mines has led to serious waste of groundwater resources in the mine area, rapid degradation of the ecological environment around the mine field, and significant increase in production and operation costs. The curtain interception and emission reduction technology provides a new water control idea for the water control in open-pit mines. The stability of the trench section is directly related to the safety and efficiency of the water cutoff curtain during construction, at the same time, it also has a great influence on the anti-seepage effect. Taking an open-pit coal mine in the eastern Inner Mongolia of China as an example, we used the two-dimensional and three-dimensional horizontal slice method to study the factors and laws affecting the stability of the long trench section, in order to explore the stability of the trench section in sandy cobble stratum during construction. The differences between the two-dimensional and three-dimensional horizontal slice methods in the calculation of safety coefficient were compared and analyzed. The stability of the trench section was simulated and analyzed with the help of FLAC3D software for two lengths of 17.5 and 22.5 m for the sand cobble stratum respectively. Combined with the above analysis results, the stability control measures of the long trench section of sand cobble stratum were derived and verified by ultrasonic testing. The results of the study show that the main factors affecting the stability of the trench section are: the nature of the formation geotechnical body, the excavation depth of the trench section, the mud level, the mud density, the difference between the mud level and the groundwater level and the length of the single width trench section. The stability of the long trench section can be increased by adjusting the mud parameters, increasing the mud level, lowering the groundwater level, optimizing the trenching sequence and controlling the trenching time. If the length of a single trench section does not exceed 21 m, the trench can be kept upright and stable, and the long trench technique is feasible.
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图 1 某露天煤矿截水帷幕工程平面图
Fig. 1 Schematic diagram of the water cutoff curtain in the open-pit coal mine
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图 4 二维水平条分法
Hc为成槽深度；zi为地下水位深度；hw为地下水位高度；hs为泥浆高度；hi为第i条岩土层厚度；θ为倾斜滑面与水平面的夹角；q为地表均布荷载；Wi为第i条岩土滑块重力；$N_i^{'}$、τi分别为滑动面上的法向力和剪切力；Fs、Fn分别为土条单元水平条间力和竖向条间力；Ui为水压力；${p_{{{\rm{s}}_i}}} $泥浆压力
Fig. 4 Schematic graph for 2D horizontal slice method
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图 6 各影响因素与安全系数关系曲线
Fig. 6 Relation curves between influencing factors and safety factors
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图 10 槽段开挖前原始地应力场云图
Fig. 10 Nephogram of the original in-situ stress field before trench excavation
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图 11 17.5 m长幅槽段稳定性分析云图
Fig. 11 Stability analysis cloud image of 17.5 m long trench section
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图 12 22.5 m长幅槽段稳定性分析
Fig. 12 Stability analysis cloud image of 22.5 m long trench section
表 1 岩土(石)层物理力学性质
Table 1 Physico-mechanical properties of soil (rock) layers
岩土层 密度/ (kg·m−3) 弹性模量/GPa 泊松比 黏聚力c/MPa 内摩擦角φ/(°) 抗拉强度/MPa 砂砾石 2 460 17.31 0.36 0 34.0 0 泥砾石 2 480 13.73 0.37 0.80 28.0 0 粗砂岩 2 790 21.11 0.27 4.00 37.8 1.00 细砂岩 2 870 29.32 0.19 5.20 34.0 1.50 炭质泥岩 2 510 8.79 0.21 3.53 32.0 0.75 煤层 1 435 2.44 0.31 0.50 24.0 0.35 
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表 2 二维和三维水平条分法验算方案及结果
Table 2 The schemes and results of checking for 2D and 3D horizontal slice method
影响因素 安全系数${\eta _{\rm{s}}}$ 槽深/m 泥浆液面/m 泥浆密度/(kg·m−3) 液位高差/m 单幅槽段长度/m 二维水平条分法 三维水平条分法 21 0 1.15 21 21 0.517 0.839 21 21 1.15 21 21 0.830 1.211 5 0 1.15 21 21 1.309 2.168 10 0 1.15 21 21 1.022 1.588 15 0 1.15 21 21 0.876 1.352 21 5 1.15 21 21 0.586 0.897 21 10 1.15 21 21 0.686 1.015 21 15 1.15 21 21 0.799 1.150 21 21 1.20 21 21 0.872 1.237 21 21 1.25 21 21 0.918 1.290 21 21 1.30 21 21 0.966 1.348 21 21 1.15 0 21 0.274 0.498 21 21 1.15 7 21 0.509 1.018 21 21 1.15 14 21 0.721 1.178 21 21 1.15 21 7 1.891 21 21 1.15 21 14 1.364 21 21 1.15 21 22.5 1.098
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表 3 泥浆的性能指标
Table 3 Performance indicators of mud
泥浆/方法 性能指标 密度/(g·cm−3) 黏度/(Pa·s) 含砂率/% 失水率/(mL·30 min–1) 泥皮厚/(mm·30 min–1) 胶体率/% pH值 新制泥浆 1.04~1.10 20~30 <4 <10 <1.0 ≥98 8~9 循环泥浆 1.15~1.25 18~30 ≤10 <15 <1.5 ≥96 8~11 检查方法 泥浆比重计 500 mL漏斗法 含砂量杯 失水量仪 失水量仪 量筒法 pH试纸
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