富水半成岩砂岩地层地铁车站深基坑变形监测与数值模拟分析

以兰州市某地铁车站深基坑为例,研究第三系富水半成岩砂岩地层条件下桩撑支护结构深基坑的变形规律。通过对围护桩体水平位移、钢支撑轴力、地表沉降等实测结果进行分析,对基坑开挖过程进行数值模拟,将数值计算结果与实测结果进行对比研究基坑的变形规律。监测结果与数值分析表明:桩体变形呈现出两头小中间大的"弓型"变形特征,围护桩水平位移最大值发生在开挖面附近;正常施工下地表沉降形态为凹槽形,若围护桩间出现明显漏水、漏砂现象时为三角形;钢支撑轴力跳跃上升并在其下一道支撑架设后受力达到最大;深大基坑工程采用钻孔咬合灌注桩作为围护及止水结构时,必须确保桩体垂直度,保证桩体施工质量达到设计要求;数值计算结果与实测结果基本一致,数值模拟可为基坑的设计和施工提供依据。

Monitoring and Numerical simulation of a Deep Foundation pit of a Metro Transfer Station in Water-rich Sandstone Strata

Based on the excavation project of a metro transfer station in Lanzhou,the deformation law of deep foundation pit engineering in special bad geological conditions( red sandstone layer) is studied based on the analysis of the displacement of fender piles and axial force of the steel supports,and by means of the simulation of the excavation process of deep foundation pit and the comparison of the results of numerical simulation with those of the measurements. The monitoring and numerical simulation results showe that the deformation of the pile presents the shape of a "bow ",most deformation of the pile appears in the surface of excavation; under normal construction,the surface settlement turns to be in a groove shape,and the deformation of the pile shows a triangle in shape in case fender piles are subject to water leak and sand leak; the steel strut axial pressure jumps up to the maximum after the next strut is put in place; where secant pile is used in deep foundation pit engineering as a retaining and sealing structure,the verticality of must be maintained to ensure pile quality; the calculation results are basically agree with the measurements and the numerical analysis provides the basis for the design and construction of foundation pit.