既有盾构隧道上方开挖基坑降水方案优化分析

Dewatering Optimization Analysis of a Deep Excavation Above an Existing Shielded Tunnel

为了解不同降水井平面布置、开启时间及工作时长等对降水效果的影响规律,优化基坑降水方案,以厦门某地铁隧道基坑零距离上跨正线盾构隧道工程为研究背景,考虑降水井平面布置和纵向各段降水井开启时间及相互影响,利用PLAXIS 3D岩土有限元程序建立3个三维渗流有限元模型,通过变化平面布置情况及降水井开启先后顺序,计算分析对基坑降水效果的影响。计算结果表明:降水井间距设置15 m较为合理;模型1因前后各排井同时工作,各井之间相互影响,而单井抽水量不高;模型2由于下一施工区段的工作井未开启,降水效果不理想;基坑分区降水时,下一排降水井的提前开启时间可为30 d左右。最终实践表明,采取的基坑降水方案可靠,基坑安全稳定。

The effect of point-well layout,starting time and operation duration on the dewatering results are evaluated in this paper and the dewatering plan of a deep excavation project over a shielded tunnel in Xiamen was also optimized.A three-dimensional seepage numerical model was established by using PLAXIS 3D commercial software to study the potential factors that affecting the dewatering results.The results show that:the spacing of well points is 15 m is an appropriate distance;In Model No.1,the single well-point did not obtain a high yield of water volume due to the interaction of well point surrounding it when they were operating at the same time.In Model No.2,the dewatering results was not ideal due the well pints for the next construction section did not operate.When a zoned dewatering plan is desired,the dewatering well point for the next stage should be operated in approximate 30 days ahead of the desired excavation date.The final field practice showed that the dewatering planed used was reliable and the excavated area was safe and stable.