宁波软土地区相连深基坑开挖施工时空效应实测分析

Analysis on time-space effect of excavation construction of adjacent deep foundation pit in Ningbo soft soil area

软土深基坑施工期变形具有明显的时空效应,以宁波软土地区相连深基坑为工程背景,对软土地区相连深基坑开挖的时空效应开展研究。基于基坑施工过程中地表沉降、地连墙水平位移、支撑轴力的监测数据,分析施工工序、开挖深度等因素对不同位置处基坑结构与土体的变形影响,并通过有限元软件对2基坑同时开挖的情况进行计算讨论。研究结果表明:采用2个基坑单独开挖的顺序,在一个基坑开挖时,已完成的地连墙或已封顶的车站结构将对这一侧的地表沉降和地连墙水平位移有较好的约束作用;地表沉降与地连墙水平位移在基坑长边上的值大于端头部分,且这2个变形值具有明显的深度效应,即随着开挖深度的增加,变形值增加更快;支撑轴力的变化主要受开挖土体的位置影响,越近的土体开挖,支撑轴力增加越大;若采用2基坑同时开挖的方式,控制中间部分地连墙的变形将是重点,施工安全也面临较大挑战。

The deformation during the construction period of the soft-soil deep foundation pit has obvious space-time effect. In the engineering background of the adjacent deep foundation in Ningbo soft soil area, the study about the time-space effect of deep foundation pit excavation in soft soil area was conducted. Based on the monitoring data of the surface settlement, horizontal displacement of diaphragm wall and the supporting axial force during the construction period of the foundation pit, an analysis was conducted on the influences of some factors such as construction process and excavation depth on the foundation pit structure and soil at different locations. The results show that the finished diaphragm wall or the capped station structure will constrain the ground settlement and the horizontal displacement of the diaphragm wall. The surface settlement and the horizontal displacement of diaphragm wall of the long side of the foundation pit is larger than that at the end. These two deformation values have obvious depth effect, that is, the value of deformation increases faster with the excavation depth increases. The changes in the support axial force is mainly affected by the position of the excavated soil. The closer the soil excavation is, the greater the axial force of the support is. If two foundation pits are excavated at the same time, controlling the deformation of the middle part of the connecting wall will be the key point, and the construction safety will also face great challenges.