近间距下穿高架群桩的基坑施工可行性

On Construction Feasibility of Foundation Pit through Viaduct Multi-piles in Close Space

应用平面有限元软件对上海某地道下穿轨道交通11号线基坑施工进行了模拟分析。基坑开挖造成的土体侧向卸载,影响着临近群桩基础的安全。分析结果表明:临近桩基侧移与围护桩变形有一定的相关性,发生最大侧移的地方均位于基坑开挖面处,而围护桩弯矩的发展变化跟支撑位置和刚度有着直接关系;基坑开挖造成的侧向卸载作用对临近桩基的影响明显大于对承台的影响;不考虑桩基侧移的情况下,侧向卸载造成摩擦群桩承载力降低量可忽略;围护结构支护状态的有效性对减少临近桩基侧移和保持群桩承载力起到关键作用。

Plane finite element software is applied to simulate analysis a subway tunnel under a foundation pit construction at Shanghai Metro L11.Lateral unloading of soil mass caused by excavation will affect the safety of adjacent pile.Analysis results indicate that: 1) there is correlation between the lateral displacement of adjacent piles and the enclosure pile deformation.Where the maximum lateral displacements occur are all located in the pit excavation surface,and the development change of enclosure pile bent moments has direct relationship with the location and stiffness of the supports;2) the lateral unloading caused by foundation pit excavation can affect the adjacent piles significantly greater than the impact on the pile cap;3) without considering the case of pile lateral displacement,the bearing capacity reduction of the friction piles caused by the lateral unloading can be ignored;4) the effectiveness of the envelope piles can play a key role to reduce the lateral displacement of adjacent pile foundations and maintain the bearing capacity of pile groups.