下伏既有地铁隧道超大深基坑支护的设计与研究

Design and Study of a Very Deep Excavation Support Above a Subway Tunnel

随着城市地铁的快速发展,越来越多新建工程的基坑需要在已运营地铁的安全保护区内建造。拟建武汉华侨城P(2018)158地块项目被运营中的地铁4号线从基坑中部下穿,基坑支护结构距区间隧道结构边线仅11 m,基坑底距区间隧道顶距离为2.6~8.2 m;周边环境异常严峻,基坑支护结构变形控制要求严格,对基坑支护设计及施工挑战性极大。另一方面,场地内高达15 m填土需卸载,卸荷工况下区间隧道结构隆起变形控制及处理也是一个重要内容。基坑设计基于安全可靠、经济合理、施工便捷以及工期可控等原则,针对地铁保护区基坑支护设计在武汉地区首次提出并采用了“上部卸载+支护桩+一层钢筋混凝土对拉梁”方案,同时为控制区间隧道上部卸载引起的隧道隆起变形,提出了对区间隧道上部相对软弱土层采用阀管注浆加固,有效地提高了隧道围岩强度,降低了卸载期间区间隧道隆起变形量。监测数据显示在整个基坑建造过程中,各项监测数据均在规范范围内并满足地铁影响评估要求,可供类似工程借鉴。

With the rapid development of the urban subway,more and more deep excavation for new projects needs to be installed in the safety protection zone of the active subway.The active Metro No 4 Line under passing the proposed OCT Wuhan Plot P(2018)158 project.The distance between the supporting structure and the regional subway tunnel structure is only 11m,and the distance from the bottom of the deep excavation to the top of the subway tunnel varies from 2.6 to 8.2m.The surrounding environment of the deep excavation is extremely complicated,and the deformation control requirements for the excavation support structure are very restrictive,which poses great challenges to the design and construction.On the other hand,the soil fills up to 15 meters in height within the proposed excavated area needs to be unloaded.The control and remediation of the heaving deformation of the tunnel structure under unloading conditions is also an important part of this project.According to the characteristics of this project,the design of the deep excavation is based on the principles of safety,reliability,economic rationality,constructability,and construction schedule.For the first time in Wuhan area,the scheme of“upper unloading+soldier pile+a layer of reinforced concrete waler beam”is proposed and adopted in the deep excavation support design of the metro protection area.At the same time,to control the tunnel heaving deformation induced by the upper unloading of the regional subway tunnel,it is proposed to use perforated pipe grouting to reinforce the poor soil layer above the tunnel.The strength of the surrounding rock mass is effectively improved,and the heaving deformation of the subway tunnel during unloading is reduced.The monitoring data during the entire dep excavation construction process shows that all the monitoring data are within the allowable range and meet the requirements of the subway impact assessment,which can be used for the reference by similar projects.