暗挖车站洞内地下连续墙施工地层效应分析

地下水资源对经济社会的可持续发展具有十分重要的作用。为了拥护国家对水资源的保护政策,北京地铁16号线在施暗挖车站——看丹站首次尝试以导洞内地下连续墙替换传统边桩施工的方式,以期达到承载和止水的双重目的。虽然施作的试验段取得了较好的效果,但北京地区地层复杂,局促低矮空间内的洞内地连墙施工能否大范围顺利推广实施仍存在争议。以北京地铁16号线看丹站、首都机场西沿线北新桥站和北京地铁7号线广渠门外站为代表,采用Midas软件对边导洞内地下连续墙施工过程进行数值模拟,揭示北京地区砂卵石、粉质黏土和砂卵石-粉质黏土互层三种典型地层条件下洞内地下连续墙施工诱发的环境响应。结果表明：(1)在其他条件相同的情况下,砂卵石地层中地下连续墙施工引起的地表沉降值最小,粉质黏土地层地下连续墙施工引起的地表沉降值最大;(2)洞内地下连续墙施工引起导洞拱顶沉降值大小排序为：砂卵石地层<砂卵石-粉质黏土互层地层<粉质黏土地层;(3)相比于砂卵石-粉质黏土互层地层及粉质黏土地层,砂卵石地层条件下,洞内地下连续墙施工引起的围岩塑性应变值及应变范围最小,对周围土体扰动较小。

Stratum Effect of Diaphragm Wall Construction with PBA Method

Groundwater resources play a very important role in the sustainable development of economy and society. In order to comply with the national water resources protection policy, Beijing metro line 16 first tried to replace the traditional side pile construction method with diaphragm wall in the pilot tunnel at Kandan station, so as to achieve the dual purpose of bearing and sealing. Although the test section has achieved good results, it is still controversial whether the continuous wall construction can be carried out smoothly in a large scale in Beijing area with complex strata and low space. This paper takes the Kandan Station of Beijing Metro Line 16, the Beixinqiao Station on the west side of the Capital Airport and the Guangqumenwai Station of Beijing Metro Line 7 as representatives. The Midas software is used to numerically simulate the construction process of the diaphragm wall in the side pilot tunnel, revealing the environmental response induced by the construction of the underground diaphragm wall in the cave under the three typical stratum conditions of sandy cobble, silty clay and sand cobble -silty clay interbed in Beijing area. The results show that: 1) under the same conditions, the surface settlement caused by diaphragm wall construction in sandy cobble stratum is the smallest, and that caused by diaphragm wall construction in silty clay stratum is the largest. 2) The order of settlement value of pilot tunnel vault caused by diaphragm wall construction in the tunnel is: sandy cobble stratum < sandy cobble silty clay interbedded stratum < silty clay stratum. 3) Compared with sandy cobble-silty clay stratum and silty clay stratum, the plastic strain value and strain range of surrounding rock caused by diaphragm wall construction in pilot tunnel are the smallest, that is to say, the disturbance to surrounding soil is smaller.