基于抽水试验的深基坑降水方案优化调整与实施

Optimized adjustment and implementation of deep foundation pit dewatering based on pumping test

摘要:

南京一过江隧道明挖段为超深基坑，有深厚强透水砂层，含水层厚度大、渗透系数大，接受长江水补给，基坑采用悬挂式止水帷幕，涌水量大，在降水井施工过程中，通过洗井试抽发现原降水方案不能满足降水要求，且偏差非常大。为确保基坑安全、顺利施工，现场边施工降水井边开展原位抽水试验，通过对试验数据的分析，并借助三维数值法进行参数反演及降水模拟，及时对开挖深度大的JD1、JD2节段的降水井管径、数量、水泵配置进行了调整。基坑内抽水试验反演的参数远大于原方案参数，实际基坑涌水量高达91000 m³/d，是原降水方案预估值42000 m³/d的2.2倍，由于及时科学地调整了降水方案，在总井数增加不多的情况了，将坑内水位降至基底以下，保证了基坑的顺利实施，充分说明了抽水试验及方案的优化调整在降水实施过程中的重要性。

Abstract:

The open-cut section of a river-crossing tunnel in Nangjing is a super deep foundation pit with think and high water permeability sand layer， where the aquifer is massively thick with large permeability coefficient， and recharged by the Yangtze River. The hanging type water cut-off curtain was used for the foundation pit due to very large water inflow. During the construction of the dewatering well， it was found that the original dewatering scheme cannot meet the requirements for dewatering through well developemt with high deviation. In order to ensure the safety and smooth construction of the foundation pit， in-situ pumping test was carried out while drilling the dewatering well. Through analysis of the test data， and parameter inversion and dewatering simulation using the three-dimensional numerical method， adjustment was made in time on the diameter， number and pump configuration of the dewatering wells in the JD1 and JD2 sections with large excavation depth . The inverted parameters of the pumping test for the foundation pit were much larger than those of the original scheme. The actual water inflow of the foundation pit was as high as 91000 m³/d， which was 2.2 times of the estimated value of 42000 m³/d of the original dewatering scheme. With the timely and proper adjustment of the dewatering scheme， the water level in the pit was reduced below the base with little increase in the total number of wells， which ensured the smooth implementation of the foundation pit， fully demonstrating the importance of dynamic adjustment of pumping test and the pumping test scheme in dewatering.