车站共墙基坑拆撑回筑结构体系受力变形特性

Stress and deformation characteristics of demolished braced back built structure system of common diaphragm wall foundation pit group in station

深基坑内支撑拆除及坑内结构回筑会改变深基坑原来支护体系的受力平衡状态,失衡荷载会引起围护结构内力重分布,对其稳定性造成影响。共墙基坑群内支撑拆除过程荷载变化机理比单独基坑更为复杂,其安全控制更为严格。本文基于前海站共墙基坑工程,通过对基坑拆撑回筑全过程数值模拟,分析内支撑拆除过程中结构受力及位移的变化规律。结果表明:1)拆撑会改变围护结构的内力状态及位移变形,且共墙侧与非共墙侧的变化规律存在显著差异:共墙侧地连墙弯矩极值与极值位置均发生变化,围护结构位移随拆撑逐渐减小,非共墙侧弯矩分布规律变化较小,围护结构位移逐渐增大。2)支撑拆除后相邻内支撑轴力会急剧上升,其中第二道、第四道轴力分别增加了30.4%、46.2%,增设临时钢支撑能有效减少轴力增量;3)回筑过程中主体结构两侧外墙位移变形较小,最大位移分别为10.57和5.74 mm;4)拆撑回筑过程地表沉降共增长了18.9%。

Deep foundation pit support removal and pit structure construction will change the force balance of the original support system of the deep foundation pit,and the out-of-balance load will cause internal force redistribution of the enclosure structure,which will affect its stability.The mechanism of load change in the process of support removal in the co-wall pit group is more complicated than that of individual pits,and the safety control is more strict.Based on the Qianhai station common wall pit project,this paper analyzes the change law of structural forces and displacements in the process of internal support removal by numerical simulation of the whole process of pit demolition and bracing back construction.The results show that:1)the demolition of bracing will change the internal force state and displacement deformation law of the enclosure structure,and there is a significant difference between the change law of the common wall side and the non-common wall side:the extreme value and the extreme value position of the ground connection wall moment on the common wall side are changed,and the structural displacement gradually decreases with the demolition of bracing,while the distribution law of the bending moment on the non-common wall side changes less and the structural displacement gradually increases;2)The axial force of adjacent internal support will rise sharply after the removal of support,among which the second and fourth axial forces increase by 30.4% and 46.2% respectively,and the additional temporary steel support can effectively reduce the axial force increment;3)The displacement deformation of external walls on both sides of the main structure during the back construction is small,and the maximum displacement is 10.57 mm and 5.74 mm respectively;4)The ground settlement during the removal of support back construction increases by a total of 18.9%.