The scale of foundation pit project has increased with the depth increasing in Northwest China .In order to ac-cumulate deep foundation pit design and construction experience of Lanzhou metro station ,based on comparison of the common supporting schemes of Lanzhou metro station ,this paper choose the bored pile with steel tube internal bracing scheme ,the Flac3D software was used to apply 3D numerical simulation analysis to typical section of foundation pit of con-struction process .Results show that :1 ) During the early period of foundation pit excavation ,the displacement of the pile top is relatively large and the distribution forward along the pile body .With pit excavation continuing ,the place of rela-tively large displacement goes down .After the internal bracing tube installed ,the displacement of horizon bracing pile shapes like")"and the maximum of displacement happens at 1/2 to 1/3 of height from pit bottom .2 ) The maximum settlement by the pit happens in the 5 to 10 meters from the outside of pile .The settlement influence range is roughly from 1 .5 to 2 times as the pit depth .So the proper optimized drilling bitten pile and steel tube internal bracing scheme can be adopted as following station supporting scheme .3 ) For dewatering project in this example ,when the dewatering depth is not big and hydrogeological condition is relatively simple ,normally pit outside well dewatering and inside ditch drainage should be used .%为了积累兰州地铁车站深基坑设计和施工经验 ,依托兰州地铁某车站对常用支护方案进行对比 ,选定钻孔灌注桩加钢管内支撑方案 ,同时 ,采用FLAC3 D软件 ,对基坑典型断面的施工过程进行三维数值模拟分析.结果发现 :基坑开挖初期 ,桩顶水平位移较大 ,沿桩身呈前倾型分布 ;随着基坑开挖 ,位移较大部位不断下移 ,钢管内支撑施工后 ,支护桩的水平位移曲线呈")"型分布 ,最大值大约位于距离坑底1/2~1/3倍坑深处 ;坑边最大沉降点距离坑边一般约为桩体外侧5 m~10 m的区域 ,沉降影响范围约为1.5倍~2倍基坑深度 ,后续车站支护可采用适当优化的钻孔咬合桩+钢管内支撑的方案 ;对于兰州地区基坑降水工程 ,当降深不是很大、水文地质条件相对简单时 ,一般可采用坑外管井降水加坑内明排措施.
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