软土深基坑开挖卸载对地下车站桩基的影响兮析

Effect Analysis of Excavation and Unloading of Deep Foundation Pit in Soft Soil Stratum on Pile Foundation of Underground Station

[目的]深厚软土地层地下车站深基坑开挖施工过程中,坑内上覆土体的开挖卸载会对先行施工的坑内超长桩基产生较为明显的影响,威胁结构稳定和工程安全。为探究大面积深基坑开挖卸载对车站基坑底群桩的影响,须分析超长桩受力变形规律。[方法]利用Midas GTSNX数值分析软件,建立某地下车站S2东端头井有限元数值计算模型,进行开挖施工模拟分析。结合该地下车站项目施工现场实际监测数据,与数值计算结果进行对比,探讨了基坑开挖对坑底群桩变形影响的规律。[结果及结论]结果表明,桩身受拉区随着开挖深度不断增大,端头井桩基最大拉力、最大压力均大于标准段;坑底桩基竖向位移量在开挖过程中不断增加,位移最大的桩出现在距离端头井边缘最远处,且在开挖后期,桩基的上浮量增量显著提高,需要实时监控桩顶竖向位移量,防止发生工程事故。

[Objective]In the excavation process of deep foundation pit of underground station in deep soft soil stratum,excavation and unloading of the overlying soil in the pit will obviously impact the previously constructed superlong pile foundation in the pit,threatening the structure stability and engineering safety.In order to explore the effects of large.scale deep foundation pit excavation and unloading on the pile group at the station foundation pit bottom,it is necessary to analyze the deformation law of the superlong pile under pressure.[Method]A numerical analysis software Midas GTS NX is used to establish a finite element numerical calculation model for the underground station S2 east end well and make the excavation simulation analysis.Based on a comparison of the on.site actual monitored data and the numerical calculation results,the deformation law of the pile group at the pit bottom affected by the foundation pit excavation is discussed.[Result&Conclusion]The results show that the pile area under tension increases with the deepening of excavation,both the maximum tension and the maximum pressure of the end well pile foundation are greater than the standard range.The vertical displacement of the pile foundation at the pit bottom continuously increases in the process of excavation.The largest pile displacement occurs at the farthest distance from the edge of the end well.In the later stage of excavation,as the incremental uplift of the pile foundation increases significantly,the vertical displacement of the pile top needs to be monitored in real time to prevent engineering accidents.