上跨铁路转体桥梁主墩基坑施工对周边土体的影响

Impact of Foundation Pit Construction of Main Pier on Surrounding Soil for a Swivel Bridge over Railway

上跨铁路转体桥梁主墩大型基坑施工会引起周边土体的附加受力和变形,可能导致邻近铁路路基沉降破坏,危及行车安全。基于有限元软件MIDAS-GTS NX对某城市公路转体桥梁主墩基坑施工过程进行三维数值模拟,通过与现场实测数据的对比,验证数值模型及计算结果的可靠性。研究表明,基坑施工引起周边土体的变形随其与基坑边缘距离的增加呈现抛物线变化;主墩工程桩设置对基坑底部隆起位移有显著抑制作用,设置工程桩工况下,坑底最大隆起位移较无工程桩工况降低91.3%;工程桩整体发生向上位移,由基坑中心向边缘方向上桩基竖向位移量呈递减趋势,基坑中心桩竖向最大位移为4.2 mm,基坑边缘桩最大位移为0.35 mm;桩身整体承受拉应力,随着埋深增大拉应力逐渐增大,桩顶处承受拉力约为桩底的1/12。最后,依据数值模拟分析结果,对上跨铁路转体桥梁主墩位置、选型及结构设计提供合理化建议。

The construction of the foundation pit of the main pier for an overpass railway bridge causes additional stress and deformation of the existing railway subgrade, and even causes subgrade settlement which endanger the operation safety. Based on the finite element software MIDAS-GTS NX, the three-dimensional numerical simulation of the construction process of main piers foundation pit of for a highway rotating bridge in a city was carried out. The reliability of the numerical model and its results were verified by comparing with the field measured data. The simulation results show that the deformation of the surrounding soil caused by the construction of the foundation pit has a parabolic change with the increase in the distance from the edge of the foundation pit;Comparing with the deformation results of piles with or without piles, it is found that the main pier piles have significant inhibiting effects on the heave displacement of the foundation pit bottom, and the maximum heave displacement of the foundation pit bottom with piles is reduced to 91.3% of that without piles;The maximum vertical displacement of the pile at the center of the foundation pit is about 4.2 mm, and the maximum displacement at the edge of the foundation pit is about 0.35 mm. The pile undertakes tensile stress, which gradually increased with the increase of the buried depth. The tensile stress at the pile top was about 1/12 of that at the pile bottom. Based on the results of numerical simulation analysis, suggestions were provided for the position selection and structural design of main piers of upper-span railway rotating bridges.