某地铁深基坑桩撑支护结构施工力学行为分析

Construction Mechanics Behavior Analysis of Pile-strut Supporting Structure of a Subway Deep Foundation Pit

研究目的:特殊红砂岩地层严重影响兰州地铁车站深基坑支护施工安全,因此研究特殊红砂岩复杂环境下深基坑施工力学行为迫在眉睫。本文以兰州地铁1号线东方红广场站深基坑桩撑支护结构为工程背景,依据现场监测结果和数值计算模型对比分析了围护结构、周边建筑物及地表沉降的位移变化规律。研究结论:(1)数值模拟结果和现场监测结果对比分析表明,两者的结果相近,变化趋势基本一致,说明运用生死单元法对基坑开挖支护分析的结果可以为深基坑的设计与施工提供有效指导;(2)现场监测桩顶水平位移最大值为10.51 mm,小于30 mm的控制值,这说明咬合桩+钢支撑的支护结构可以有效地控制兰州特殊红砂岩地层基坑位移;(3)随着基坑开挖和支护的持续进行,桩身的前倾型变化曲线逐渐成为"鼓肚"形,最大测斜值为10.56 mm,发生于2/3倍的开挖深度附近;(4)随着基坑的不断开挖,周边建筑物距离车站越远,其竖向沉降位移越小;(5)基坑周边的最大沉降发生于距离基坑边缘1/3倍坑深处;(6)本研究成果可为兰州地区类似特殊地层地铁深基坑的设计与施工提供指导。

Research purposes:The special red sandstone formation seriously affects the construction safety of deep foundation pit in Lanzhou subway station.Therefore,it is urgent to study the construction mechanical behavior of deep foundation pit in the complex environment of special red sandstone.In this paper,based on the site monitoring results and numerical calculation model,taking the pile-strut supporting structure of Lanzhou Metro Line No.1 Dongfanghong Square Station deep foundation pit as the engineering background,the law of displacement variation of retaining structures,surrounding buildings and surface subsidence is analyzed comparatively.Research conclusions:(1) The results of numerical simulation and field monitoring by comparative analysis indicate that the results are close and have the same change trend,which shows that the results of the analysis to foundation pit excavation supporting by using the birth and death element method can provide effective guidance for the design and construction of deep foundation pit.(2) The maximum value of horizontal displacement pile tip monitored on site is 10.51 mm and is less than the control value of 30 mm,which indicates that the supporting structure of occlusal pile and steel support can effectively control the displacement of Lanzhou special red sandstone formation foundation pit.(3) As foundation pit excavation and supporting continues,the forward heeling curve of pile body gradually becomes the shape of "drum belly" and the location where the maximum measured slope value is 10.56 mm is located near 2/3 times the depth of the excavation.(4) With the continuous excavation of foundation pit,the vertical settlement displacement of the surrounding buildings decreases with the further away from the station.(5) The maximum settlement around the foundation pit located 1/3 times the depth of the pit.(6) The research result can provide guidance for the design and construction of subway deep foundation pit of similar special stratum in Lanzhou.