砂土地区深基坑稳定性评价及力学效应分析

Stability Assessment and Mechanical Effects Analysis on Deep Foundation Pit in Sandy Soil

结合某地铁车站基坑开挖工程,基于基坑支护结构的现场实测数据,对排桩内支撑基坑支护体系桩顶水平位移,桩体侧向位移及基坑周边土体沉降量进行分析,得出基坑围护结构各项位移和周边土体沉降随时间及开挖深度的变化规律.建立研究区二维有限元模型,并将实测数据与模拟值进行对比,研究支护结构内力变化及桩后土体应力状态.研究结果表明:基坑长边桩顶水平位移约为短边桩顶水平位移的3倍,桩体最大侧向变形量位于1/2H(H为基坑开挖深度)处;基坑开挖及降水引起地面沉降范围约3H,基坑周边各监测断面最大沉降量出现在距基坑边22 m处(约0.82H^0.96H),内支撑架设有助于增大基坑整体稳定性.

The horizontal and lateral displacements of pile-cap and the ground settlement of the surrounding soils of a foundation pit of a subway station in sandy soil were investigated based on the in-situ monitoring data.The changing rules of the displacement of the inner supporting system and the deformation of the surrounding soils with excavation time and excavation depth were obtained.A two-dimensional finite element model was built to analyze the internal forces of the supporting structures as well as the stress redistribution in soils behind those piles.Numerical results agree well with the in-situ monitoring data.Results indicate that the horizontal displacement of the pile-cap in the long side direction of the foundation pit is three times than that in the short side direction;the maximum lateral displacement of the piles occurs at 1/2 H(H is the depth of the foundation pit).The range of the ground settlement induced by excavation and drainage is 3 H.The largest deformation in the surrounding soil is located 22 m away from the excavation edge(0.82 H^0.96 H).It is found that the inner supporting system can effectively improve the stability of the foundation pit.