兰州某地铁车站深基坑开挖变形特性及环境影响分析

针对兰州城区工程地质水文条件复杂的问题,为了研究该地区地铁车站深基坑开挖过程中支护结构的变形受力特点和对周边环境的影响,以迎门滩站深基坑工程为典型案例进行分析。该车站基坑所在区段属黄河漫滩区,地铁穿过地层主要为卵石土,水位5～8 m。该基坑围护结构采用钻孔灌注桩+钢管内支撑体系。采用PLAXIS 3D有限元分析软件对该基坑建立三维有限元计算模型,土体本构模型采用土体硬化(HS)模型,依据工程实际开挖工况进行分部开挖计算,根据计算结果对桩撑式支护结构的变形和受力及基坑周边地表和地下管线的变形进行了分析。结果表明:围护桩的变形量、地表沉降量和管线位移量会随着基坑开挖深度的增加有逐渐累积的趋势,但在架设内支撑并施加预应力后,这些变形量的增速会减缓甚至变形量会减小。内支撑施加预应力之后自身轴力会有较大增加,之后基本保持不变,对其他内支撑轴力的影响较小。各变形量均在控制范围之内,满足设计和环境要求,表明该深基坑采用的钻孔灌注桩+钢管内支撑支护体系设计合理。研究成果可为后续黄土地区类似地铁车站深基坑工程建设提供一定的参考依据。

Deformation characteristics and environmental impact analysis of deep foundation pit excavation in a subway station in Lanzhou

Aiming at the complex engineering geological and hydrological conditions in Lanzhou urban area，in order to study the deformation and stress characteristics of supporting structure and its influence on surrounding environment during the excavation of deep foundation pit of metro station in this area，Yingmantan Station deep foundation pit project is analyzed as a typical case. The section where the foundation pit of the station is located belongs to the floodplain area of the Yellow River. The stratum through which the subway passes is mainly pebble soil with a water level of 5 ～ 8 m. The retaining structure of the foundation pit adopts bored pile and steel pipe internal support system. The three-dimensional finite element model of the foundation pit is established by using PLAXIS 3D finite element analysis software，and the soil hardening ( HS) model is adopted in the soil constitutive model. According to the actual excavation conditions of the project，the partial excavation calculation is carried out，and the deformation and stress of the pile-supported supporting structure and the deformation of the surface and underground pipelines around the foundation pit are analyzed according to the calculation results. The results show that the deformation of the retaining piles，surface settlement and pipeline displacement will gradually accumulate with the increase of the excavation depth of the foundation pit，but after the erection of internal supports and application of prestress，the growth rate of these deformations will slow down or even the deformation will decrease. After applying the prestress，the axial force of the inner support will increase greatly，and then remain basically unchanged，with little influence on axial forces of others inner supports. Each deformation is within the control range，which meets the design and environmental requirements. It shows that the design of bored pile and steel pipe internal support system used in the deep foundation pit is reasonable. The results of this research can provide some reference for the construction of similar deep foundation pit in metro stations in the subsequent loess areas.