二元结构含水层悬挂式帷幕深基坑降水计算方法研究

Study on calculation method of dewatering in deep excavation with suspended cut-off curtain in dual aquifer

帷幕结合基坑内降水的方案是深基坑工程中地下水控制的主要趋势,而至今业内对悬挂式帷幕降水条件下的设计尚无统一的计算方法。本文以汉口长江I级阶地某基坑工程为实例,基于二元结构含水层特点,提出了承压—无压条件下的修正大井法,并分别运用修正大井法、半封闭承压含水层非稳定流半解析法和数值模拟等方法,对不同帷幕深度条件下基坑涌水量和降深进行了计算,并开展对比分析。研究结果表明:承压—无压修正大井法较其它大井法更能刻画二元结构基坑降水帷幕的实际作用;半封闭承压含水层非稳定流半解析法在小程序辅助下,可实现水位降深的计算,且与数值解吻合度较高,可满足此类基坑降水设计的便捷计算需求。

The combined use of the cut-off curtain and dewatering is the main trend of groundwater control in the deep excavation project. So far there is no general accepted calculation method for the design of dewatering with suspended cut-off curtain. A case study of an excavation project in the first terrace of Yangtze River in Hankou was carried out. Based on the dual aquifer,a modified large-well-method under the condition of confined-unconfined aquifer is proposed. Then,several methods including modified largewell-method( MLWM),semi-closed confined aquifer semi-analytical method( SCASM) of unsteady flow and numerical simulation were used to calculate the dewatering yield and the drawdown distributions under the condition of different cut-off curtain depth in the excavation project. The results show that the confinedunconfined WLWM is better than other large-well-methods in describing the actual effect of the groundwater cut-off curtain in excavation of dual aquifers. The SCASM can realize the calculation of groundwater level drop with the assistant of a small program,and the results is highly consistent with the numerical solution. It can meet the convenient calculation requirements of such dewatering design in deep excavation.