Application of MODFLOW-CFPv2 model in karst tunnel water inrush and its impact on groundwater environment: Example of the Mengkuanggou karst water system in Heqing County, Yunnan Province
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摘要:
滇中地区构造复杂、岩溶发育, 隧洞突涌水及泉流量衰减是隧洞施工过程中最棘手的问题之一。锰矿沟岩溶水系统岩溶管道化程度高, 岩溶裂隙与岩溶管道2种含水介质差异显著。采用MODFLOW-CFPv2双重介质数值模型对锰矿沟岩溶水系统展开数值模拟研究, 精细刻画岩溶管道与引水隧洞, 进而掌握隧洞施工对地下水流场影响以及泉流量变化的规律。结果表明: (1)MODFLOW-CFPv2模型能够刻画岩溶地区复杂的地质结构, 较好地模拟研究区地下水位的动态特征和岩溶泉流量响应特征。(2)在强排工况下隧洞单位长度最大涌水量为164 m3/(d·m), 单位长度稳定涌水量为69 m3/(d·m), 锰矿沟岩溶泉流量也出现显著下降的趋势, 在模拟期内平均泉流量从天然条件下1 578 L/s下降至1 098 L/s, 总体减少了30.4%;峰值泉流量从2 133 L/s下降至1 375 L/s, 减少了35.5%, 强排工况施工会对隧洞工程施工和地下水环境造成显著影响; 限排工况下隧洞单位长度最大涌水量为39 m3/(d·m), 单位长度稳定涌水量为24 m3/(d·m), 隧洞单位长度涌水量显著降低, 锰矿沟岩溶泉流量的下降趋势也得到了一定程度的改善, 模拟期内平均泉流量降低至1 284 L/s, 减少了18.6%, 峰值泉流量降低至1 617 L/s, 减少了22.1%。采用的MODFLOW-CFPv2双重介质模型具有较精确刻画岩溶区管道、溶洞、裂隙共存的高度非均质岩溶水系统的能力, 能够定量评价香炉山隧洞施工对锰矿沟岩溶水系统地下水流场及泉流量的影响, 为香炉山隧洞工程的突涌水灾害防治提供参考依据, 也为岩溶地区复杂地质条件下地下水研究提供借鉴经验。
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关键词:
- 双重介质 /
- 数值模拟 /
- 引水隧洞 /
- 泉流量 /
- MODFLOW-CFPv2模型 /
- 岩溶隧道 /
- 突涌水 /
- 云南锰矿沟岩溶水系统
Abstract:Objective In the central Yunnan region, the geological structure is complex and karst formations are prevalent. Sudden water gushing and attenuation of spring flow are among the most difficult problems in tunnel construction. The Mengkuanggou karst water system exhibits a high degree of karst conduitization, with significant differences between karst fissures and karst conduits.
Methods This study employs the MODFLOW-CFPv2 dual medium numerical model to simulate the karst water system of Mengkuanggou, providing a detailed description of karst pipeline and diversion tunnel to understand the influence of tunnel construction on groundwater flow and spring flow.
Results The results show that (1) The MODFLOW-CFPv2 model can describe the complex geological structure of karst areas, and simulate the dynamic characteristics of the groundwater level and the response characteristics of karst spring flow in the study area. (2) Under the condition of strong discharge, the water inflow per unit length of the tunnel is 164 m3/d·m, with a stable water inflow of 69 m3/d·m, while the Mengkuanggou karst spring flow shows a significant downwards trend. During the simulation period, the average spring flow decreased from 1 578 L/s under natural conditions to 1 098 L/s, an overall decrease of 30.4%, and the peak flow rate decreased from 2 133 L/s to 1 375 L/s, a decrease of 35.5%. The construction of strong discharge conditions will have a significant impact on tunnel construction and the groundwater environment. Under the condition of limited discharge, the maximum water inflow of the tunnel is 39 m3/d·m, and the stable water inflow is 24 m3/d·m. The water inflow of the tunnel is significantly reduced, and the downwards trend of the karst spring flow in Mengkuanggou is also improved to a certain extent. During the simulation period, the average spring flow is reduced to 1 284 L/s, a reduction of 18.6%, and the peak flow is reduced to 1 617 L/s, a decrease of 22.1%.
Conclusion The MODFLOW-CFPv2 dual-medium model used in this study accurately describes highly heterogeneous karst water systems with pipelines, karst caves and fissures in karst areas. It can be used to quantitatively evaluate the karst water of Mengkuanggou during Xianglushan Tunnel construction.
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表 1 研究区含水层概化
Table 1. Aquifer generalization in the study area
概化层 岩性 厚度/m 含水层特性 第一层 灰岩、白云质灰岩和白云岩 300~1 000 岩溶裂隙水含水层 第二层 泥质灰岩夹少量粉砂岩及页岩、砂岩 90~120 裂隙水或岩溶
裂隙水含水层第三层 玄武岩 200~500 裂隙水含水层 表 2 模型参数设置
Table 2. Model parameter settings
基岩参数 水平渗透系数/(m·d-1) 垂向渗透系数/(m·d-1) 重力给水度 弹性给水度/m-1 降雨入渗系数 第一层 补给区 0.15 0.035 0.05 / 0.38 径流区 0.2 0.02 0.06 / 0.36 排泄区 0.3 0.03 0.07 / 0.33 第二层 补给区 0.03 0.006 0.02 0.000 1 / 径流区 0.04 0.005 0.03 0.000 15 / 排泄区 0.05 0.004 0.04 0.000 2 / 第三层 补给区 0.01 0.003 0.007 0.000 1 / 径流区 0.02 0.002 0.008 0.000 1 / 排泄区 0.03 0.001 0.01 0.000 1 / 管道参数 直径/m 下雷诺数 上雷诺数 粗糙度/m 管壁交换系数/(m2·d-1) 上游段(Ⅰ) 0.9 2 300 4 000 0.000 1 2 中游段(Ⅱ) 1.0 2 300 4 000 0.000 1 6 下游段(Ⅲ) 1.1 2 300 4 000 0.000 1 8 表 3 不同施工工况隧洞单位长度涌水量预测汇总
Table 3. Summary of the tunnel water inflow predictions under different construction conditions
施工工况 限排工况 强排工况 单位长度涌水量/(m3·d-1·m-1) 最大 稳定 最大 稳定 39 24 164 69 -
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