考虑渗流效应的深基坑大型止水屏障分析方法及其应用

Analytical procedure for massive water-sealing barriers used in deep excavations considering seepage effect and its application

本文介绍了一种深基坑大型止水屏障(部分重叠的高压旋喷桩组成)的分析方法,该方法考虑了其两个关键的因素(渗透性与材料强度)。随后,通过对一个算例进行了分析和讨论。结果表明,在基坑止水屏障参数设计时应主要考虑其拉裂破坏模式,其中最大允许渗流量是重要的设计指标之一,其对确定基坑止水屏障设计参数具有十分显著的影响。与本文提出的设计方法相比,由于忽略止水屏障结构自身渗透性能和材料强度对结构安全的贡献,采用稳定平衡法或渗流稳定平衡法进行确定基坑止水屏障设计参数是相对保守的。在此基础上,以福州地铁某深基坑工程为例,采用本文提出的设计方法,确定了深基坑止水屏障厚度与深度的范围值。最后,现场抽水试验结果表明现场基坑止水屏障的水密性能十分良好。

This paper presents an analytical procedure for massive water-sealing barriers(MWSBs)that are made of partially overlapped jet-grouting columns used for deep excavations,in which two crucial factors of the permeability and strength of jet-grouted materials are considered.Subsequently,a calculation example is analyzed and discussed.Results show that“tension failure”mechanism is a major concern for the structural failure during a design of MWSBs.The maximum allowable seepage discharge is a crucial index for the design of MWSBs,which has a significant influence on determining the design parameters of MWSBs.Compared with the design procedure for MWSBs that is proposed in this paper,the design parameters of MWSBs determined by the stability equilibrium and seepage stability equilibrium approaches are conservative due to the fact that it fails to consider the permeability or strength of jet-grouted materials that makes a contribution to the structural safety.Based on the proposed design method,the ranges of both the thickness and depth of MWSBs for a case history of subway excavation in Fuzhou,China were determined.Finally,field pumping test results showed that the water-tightness performance of MWSBs performed at site was quite well.