复杂地质条件下超深竖井的渗控措施及效果分析

Analysis on seepage control measures and their impact on an ultra deep foundation pit in complex geological conditions

富水区复杂地质条件下超深竖井工程施工期安全风险大,合理的渗控措施对保障超深竖井基坑施工期安全至关重要。以深圳市罗田水库—铁岗水库隧道工程超深竖井为例,通过构建超深竖井基坑三维渗流有限元模型,揭示了基坑开挖过程中断层破碎带和地连墙完整性等因素对渗流场的影响规律,并评估了竖井渗漏量及其渗透稳定性等。结果表明:①如不设地连墙,竖井开挖到底时渗流量高达4018m^(3)/d,且对周边区域地下水有明显影响,影响范围大于100 m。②设置高喷式地连墙的渗控效果显著,分步开挖过程中覆盖层没有渗透稳定问题,浇筑底板后渗漏量可降至10m^(3)/d以下,同时地连墙也起到隔离区域地下水的作用,竖井周边未形成降水漏斗,地下水位基本没有变化。③若地连墙完整性出现问题其渗透系数增大一个量级时,相应的渗漏量可能增大2倍以上。④断层性态对竖井渗漏量也有一定影响,断层充填物渗透系数由10^(-4) cm/s增大至10^(-3)~10^(-2) cm/s,渗漏量将增大12~80倍。对于超深竖井,特别是在地质情况复杂、有断层通过的部位,应高度重视竖井地连墙施工质量,保证墙体接头部位的防渗效果,以满足竖井渗流安全要求。研究成果可为超深竖井基坑渗控设计和施工提供依据。

The safety risks associated with ultra deep foundation pit constructions in water-rich areas under complex geological conditions are high.Effective seepage control measures are critical to ensuring the safety of foundation pits during construction.Using the ultra-deep foundation pit of the Luotian Reservoir to Tiegang Reservoir Tunnel Project in Shenzhen City as a case study,a three-dimensional finite element model was developed to assess the seepage behavior in the foundation pit.The model evaluated the influence of factors such as fault fracture zones and the integrity of the ground walls during excavation,as well as the overall seepage stability of the foundation pit.The results indicated that:①Without a ground wall,the seepage flow during foundation pit excavation could reach 4018m^(3)/d,significantly affecting the surrounding groundwater,with an impact radius of over 100 m.②The use of high-pressure sprayed ground walls showed effective seepage control,with no stability issues during stepwise excavation.Once the bottom plate was poured,leakage was reduced to less than 10m^(3)/d.Additionally,the ground wall helped isolate surrounding groundwater,preventing the formation of a groundwater depression cone and maintaining a stable groundwater level.③If the ground wall's integrity was weakened of increasing the permeability by an order of magnitude,leakage may multiplied more than double.④Fault texture also influenced foundation pit leakage,if permeability in fault fillers increases from 10^(-4) cm/s to 10^(-3)~10^(-2)cm/s the leakage would rise by 12 to 80 times.For ultra deep vertical shafts,especially in areas with complex geological conditions and passing faults,high attention should be paid to the construction quality of the ground wall of foundation pits,ensuring the anti-seepage effect of the wall joints to meet the safety requirements of vertical shaft seepage.These findings can provide a valuable reference for the design and construction of seepage control in ultra-deep foundation pits.