超大深基坑开挖对邻近地铁隧道变形影响

Influence of excavation of super deep foundation pit on deformation of adjacent metro tunnel

为研究超大深基坑开挖对临近地铁隧道变形影响,基于实际工程概况,利用有限差分软件FLAC3D建立三维模型,对基坑开挖过程中邻近地铁隧道侧的坑外地表沉降、围护结构地下连续墙变形和地铁隧道整体变形规律进行研究,并分析基坑与邻近地铁隧道相对位置对地铁隧道侧移的影响。研究结果表明:在基坑开挖作用下,邻近地铁隧道侧的坑外地表沉降受地铁隧道的影响,出现了3个沉降凹槽,地表最大沉降值出现在第1个凹槽,并且随着开挖深度的增加逐渐向右移动,第2个凹槽逐渐消失,第3个凹槽逐渐形成但不明显,与无地铁隧道影响时相比,其最大沉降值增大了10%;随着开挖深度的增加,地下连续墙侧移曲线由悬臂形变成近似中间大、两头小的抛物线形,没有出现脚踢形曲线,设置内支撑可以有效限制地下连续墙发生较大的侧向变形,保证基坑相对稳定;地铁隧道整体变形呈对称分布,水平位移呈倒八字变形,以水平位移为主,而竖向位移较小;当地铁隧道离地下连续墙距离L小于20 m时,对地铁隧道影响显著,为主要影响区域;地铁隧道最大侧移随着埋深增加,先增大后减小,增长趋势和无地铁隧道时的地下连续墙侧移大致相似,地铁隧道-土-地下连续墙相互作用复杂,受地铁隧道和基坑相对位置影响显著。

In order to study the influence of the excavation of an super deep foundation pit on the deformation of the adjacent metro tunnel, based on the actual project profile, a three-dimensional model was established using the finite difference software FLAC3 D. In the process of foundation pit excavation, the surface settlement of the adjacent metro tunnel, the deformation of the diaphragm wall of the retaining structure and the overall deformation of the metro tunnel were studied, and the influence of the relative position of the foundation pit and the adjacent metro tunnel on the lateral displacement of the metro tunnel was analyzed. The results show that under the action of excavation of foundation pit, three settlement grooves are appeared on the outer surface of the pit adjacent to the subway tunnel due to the influence of the metro tunnel. The maximum ground settlement value appear in the first groove, and gradually moved to the right as the excavation depth increase, the second groove gradually disappear, and the third groove gradually formed but it is not obvious. The maximum settlement value is 10% larger than that without the influence of the metro tunnel. With the increase of excavation depth, the lateral displacement curve changes from cantilever shape to parabola shape, which is similar to the middle and two small ends. There is no kick shape curve. The internal support can effectively limit the large lateral deformation of the diaphragm wall and ensure the relative stability of the foundation pit. The displacement of the metro tunnel is symmetrical, its horizontal displacement is inverted, which is mainly horizontal displacement, while its vertical displacement is small. When the distance between the metro tunnel and the diaphragm wall is less than 20 m, the influence on the subway tunnel is significant, which is the main influence area. With the increase of buried depth, the maximum lateral displacement of the metro tunnel increases first and then decreases. The growth trend is similar to the lateral movement of the diaphragm wall without the metro tunnel. The interaction of the subway tunnel-soil-diaphragm wall connection wall is complex, which is significantly affected by the relative position of the subway tunnel and the diaphragm wall. 2 tabs, 11 figs, 25 refs.