坑底加固对深厚软土狭长基坑变形影响研究

Influence of pit bottom reinforcement on deformation of long and narrow foundation pits in deep soft soil

为研究坑底加固对基坑变形及周边环境的影响规律,以广州南沙港铁路明挖隧道深厚软土狭长基坑为例,选取典型基坑断面建立三维计算模型,通过现场监测和数值模拟结果对比,验证有限元计算的合理性,在此模型的基础上,探讨被动区土体加固参数及承载桩加固设计参数变化对基坑变形的影响。结果表明:坑底土体加固对基坑变形控制效果影响显著,加固宽度和加固深度影响效果相当,可控制墙体水平位移35%~40%,其中加固深度建议取0.15H~0.31H(H为基坑开挖深度),加固宽度建议取0.61H~0.92H,当超出有效范围,加固效果变得不显著;坑底承载桩加固对基坑变形控制效果差距不大,墙体水平位移与地表沉降随着桩长及桩径的增加而减小,随着桩间距的增加,墙体水平位移呈增大变化趋势,不利于基坑变形控制,但地表沉降近似线性减小,且变化速率较小,地表沉降最大沉降位置距基坑边缘约0.77H,主要影响范围约3.0H。研究成果可为软土地区基坑变形控制及类似工程加固设计提供参考。

To study the effect of pit bottom reinforcement on the deformation of foundation pit and surrounding environment,Guangzhou Nansha port railway open-cut tunnel deep soft soil narrow-long foundation pit is taken as an example,a typical foundation pit section is selected to establish a three-dimensional calculation model,and the rationality of finite element calculation is verified by comparing the results of field monitoring and numerical simulation.Based on this model,the influence of modification of soil reinforcement parameters and bearing pile reinforcement design parameters of the passive area on the deformation of foundation pit is explored.The results show that the soil reinforcement of the pit bottom has a significant influence on the control effect of the deformation of foundation pit,the effect of reinforcement width and reinforcement depth is equal,and the horizontal displacement of wall can be controlled by 35%~40%,the reinforcement depth is recommended to be 0.15H~0.31H(H equals to the excavation depth of the foundation pit),and the reinforcement width is recommended to be 0.61H~0.92H,when the effective range is exceeded,the reinforcement effect becomes no longer obvious;the effect of bearing pile reinforcement on the control of deformation of foundation pit is not different,the horizontal displacement and surface settlement of the wall would decrease with the increase of pile length and pile diameter,with the increase of pile spacing,the horizontal displacement of the wall shows a trend of increasing,which is not conducive to the control of deformation of foundation pit,but the surface settlement increases in a near-linearly manner,and the change rate is relevantly small,the maximum settlement position is about 0.77H from the edge of the foundation pit,and the main influence range is about 3.0H.The research results can provide reference for the control of deformation of foundation pit in soft soil areas and similar engineering reinforcement design.