紧邻大直径盾构隧道的基坑开挖实测分析

Analysis of the measurements of excavation adjacent to large-diameter shield tunnel

基于杭州某紧邻大直径盾构隧道的基坑工程,通过实测数据分析了基坑开挖过程中的变形性状规律。结果表明,基坑开挖过程中深层土体侧移曲线呈弓形分布,且侧移量的大小具有长边与空间效应,开挖影响程度沿远离基坑坑角的方向逐渐衰减;开挖工后周围地层流变和支撑应力松弛具有明显的时间效应,扰动影响不容忽视;周围地表沉降沿基坑向外和沿基坑长边方向均呈“凹槽”分布模式,且基坑长边中部距基坑1.0倍开挖深度范围的地表变形沉降最大;基坑开挖卸荷,导致坑底土体隆起变形,带动围护结构上移,建议尽量缩短基坑开挖过程中的暴露时间,尤其是深层土体,尽快架设支撑以及浇筑底板,可有效抑制隆起与侧向变形。

Based on a foundation pit project adjacent to a large-diameter shield tunnel in Hangzhou, the deformation behavior of the excavation is analyzed through measured data. The results show that the lateral displacement curve of the deep soil is in a bow-shaped distribution during the excavation. Moreover, the amount of the lateral displacement has long-side and spatial effects, and during excavation the influence gradually decreases along the direction away from the corner of the foundation pit. After the excavation, the rheology of the surrounding formation and the relaxation of the supporting stress have obvious time effects, and during exaction the influence of disturbance cannot be ignored. The surrounding ground settlement has a ‘groove’ distribution pattern along the outward direction and along the long side of the foundation pit. And the ground settlement in the middle part of the long side of the excavation is the largest in the range of 1.0 times the excavation depth. The unloading results in the uplift deformation of the soil at the bottom of the pit, which drives the upward movement of the retaining structure. It is recommended to minimize the exposure time during the excavation, especially for deep soils. Erection of supports and pouring of the floor as soon as possible can effectively restrain uplift and lateral deformation.