主动控制轴力作用下基坑围护结构强度研究

Investigating the strength of foundation pit bracing structure with active control of axial force

伺服钢支撑可通过主动补偿损失轴力控制基坑变形,虽应用良多但对其作用的围护结构强度问题研究甚少。基于力学原理,采用增量法对不同钢支撑轴力作用下的围护结构强度进行计算,得到了不同工况作用下围护结构的弯矩、剪力变化规律。以上海浦东南路站2号出入口基坑和浦东南路站基坑工程为依托,采用Plaxis 2D数值模拟并得到了不同伺服钢支撑轴力施加工况以及极限承载状态轴力组合工况下的围护结构内力分布。结果表明,在伺服钢支撑轴力逐渐增大作用下,围护结构迎土侧弯矩逐渐增大,背土侧弯矩先减小后增大,剪力先减小再增大,最大弯矩与最大剪力均未超过地连墙可承受极限值,背土侧配筋需结合伺服钢支撑轴力相应提高配筋率;各伺服钢支撑极限承载组合工况中若干工况超过地连墙设计极限值,采用伺服控制系统不可依靠单一增加作用力来提高主动控制效果。

The servo steel strut can control the deformation of the foundation pit by actively compensating for the lost axial force.Although it has been widely used,there is little research on the strength of the bracing structure that it acts on.Based on the principle of mechanics,the incremental method was used to calculate the strength of the bracing structure under different axial forces of the steel strut,and thus,the changes in the bending moment and shear force of the bracing structure were obtained for different working conditions.Based on the foundation pit of the No.2 entrance and exit of Shanghai Pudong South Road Station and the foundation pit of Pudong South Road Station,numerical simulation was carried out using Plaxis 2D.The internal force distributions of the bracing structure were obtained under different working conditions of increasing the axial force on the servo steel strut and axial force combination at the ultimate load state.When the axial force on the servo steel strut increased,the bending moment on the soil side of the bracing structure gradually increased,but the bending moment on the excavated side first decreased and then increased.Meanwhile,the shear force first decreased and then increased.Neither the maximum bending moment nor the maximum shear force exceeded the bearing capacity of the diaphragm wall.The results also suggested that the number of steel reinforcement at the excavated side of the diaphragm wall needs to be increased accordingly while the axial force of the servo steel strut increased.Some of the working conditions in the ultimate load combinations of servo steel struts exceeded the design limit of the diaphragm wall.The beneficial effect of the servo control system cannot be always achieved by simply increasing the axial force.