兰州地铁深基坑围护结构选型分析

Selection Analysis of Deep Foundation Pit Envelops in the Construction of Lanzhou Metro

为了积累兰州地铁车站深基坑设计和施工经验,填补兰州地区地铁深基坑的桩撑支护设计空白,结合兰州地铁深基坑工程对土钉墙(复合土钉墙)、地下连续墙、排桩预应力锚杆和排桩内支撑四种围护方案进行对比,选定钻孔灌注桩加钢管内支撑支护方案。根据基坑开挖监测结果发现:随着基坑开挖深度的增加,各开挖阶段水平位移与深度变化和内支撑及预应力的施加有关,基坑中部圈梁的侧移最大;围护桩由于下端嵌固,上端被支撑,桩体变形曲线逐渐向"大肚"形变化,最大水平位移产生的位置也相应下移。桩撑基坑开挖过程中,应减小悬臂阶段持续时间,尽早施工内支撑且适当施加预应力,加快基础施工进度,防止因土体流变而产生较大的位移。

In order to accumulate experience in the design and construction of deep excavation of metro station in Lanzhou,fill the blank of supporting structure design for deep foundation pits,four supporting structure design schemes,namely soil-nailing wall（ composite soil-nailing wall）,underground continuous wall,inner prestressed pile and anchor pile support were compared based on the situation of the deep excavation pit of Lanzhou metro. And then the scheme of inner supporting structure with bored piles and steel pipes was selected. According to the monitoring results of the excavation it is found that with the increase of excavation depth,the horizontal displacement and the depth of the excavation are affected by the supporting structure and the application of prestress; the largest lateral displacement occurs at the ring beam in the middle of the excavation pit; due to the fixation of the lower part of the supporting piles and the supporting structure for the upper part,the deformation curves of the piles present a sideway＂U＂shape,with the corresponding descent of the location of the largest horizontal displacement. Therefore during the construction of the supporting file foundation,the construction time using cantilevers should be reduced,the construction of the inner supporting structure should be conducted as soon as possible with appropriate prestress. Moreover,the construction progress should be speeded to avoid a larger displacement caused by water and soil loss.