降雨影响下基坑开挖施工对邻近基桩变形响应分析

Deformation response of adjacent pile induced by foundation pit excavation under the influence of rainfall

目前关于基坑开挖对邻近基桩变形响应的简化理论解研究,还较少考虑基坑开挖中支护作用的影响,尤其是没有考虑降雨环境带来的土工影响。基于一种适用于不同降雨工况的分层假定Green-Ampt模型来模拟降雨入渗过程,采用两阶段分析方法,研究了降雨影响下基坑开挖与邻近基桩相互作用的问题。首先,考虑基坑开挖土体卸荷、围护结构及支撑结构的影响,采用Mindlin基本解,分析降雨影响下基坑开挖施工导致邻近基桩位置的土体附加应力;然后,基于Pasternak双参数地基模型,探讨基桩与土体之间的相互作用,求得降雨影响下单桩和群桩随降雨历时变化的水平变形响应。通过工程监测数据与理论计算结果进行对比,获得了较好的一致性。此外,也针对降雨敏感参数(降雨强度、饱和渗透系数、初始含水率、基质吸力)与基桩敏感参数(边界条件、支撑刚度、桩径、开挖深度、桩与基坑间距)进行了影响因素分析。分析结果表明,所提出的理论方法可较好地反映降雨影响下基坑开挖施工对邻近基桩的变形响应;降雨对邻近基桩变形影响显著,降雨参数敏感程度依次为:降雨强度>初始含水率>饱和渗透系数>基质吸力;随着降雨历时的增长,湿润层发展深度不断增大,其发展速率呈现出逐渐衰弱并趋近于土体饱和渗透系数的规律,基坑开挖引起的邻近基桩位移也随之越来越大,其顶部位移变化速率逐渐减小后收敛至某一特定值;支撑刚度和基桩与基坑距离越小,基桩受到降雨历时的影响程度就越大;不同桩径的基桩受到降雨历时的影响程度基本相同;开挖深度越大,基桩受到降雨历时的影响程度就越大。

Currently,the simplified analysis for the deformation response of adjacent piles by excavation has seldom considered the influence of supporting action,especially the geotechnical influence caused by the rainfall environment.Based on the stratified hypothetical Green-Ampt model applicable to different rainfall conditions to simulate the rainfall infiltration process,a two-stage method was proposed to analyze the interaction between the excavation and the adjacent pile under the influence of rainfall.In the first stage,considering the influence of soil unloading,retaining,and supporting of excavation,the Mindlin solution was used to analyze the additional stresses in the soil at the adjacent pile foundations caused by the excavation of the foundation pit under the rainfall.In the second stage,based on the Pasternak foundation model,the interaction between pile foundations and soil was explored to obtain the horizontal deformation response of single piles and groups of piles under the influence of rainfall with the rainfall duration.The monitoring data from existing engineering were compared to the theoretical calculation results with good agreements.In addition,the parameters of rainfall(rainfall intensity,saturated permeability coefficient,initial water content,matric suction)and pile(boundary conditions,brace stiffness,pile diameter,excavation depth,distance between piles and foundation pit)were analyzed to investigate the influences on pile deformation.The results show that the proposed theoretical method can better reflect the deformation response of foundation excavation on adjacent pile foundations under the rainfall.The rainfall has a significant influence on the deformation of the adjacent pile,and the sensitivity of rainfall parameters is as follows:rainfall intensity>initial water content>saturated permeability coefficient>matric suction.With the increase of the rainfall duration,the development depth of the wet front continues to increase,and its development rate shows a gradual weakening law until it approaches the saturated permeability coefficient.The displacement of adjacent piles caused by the excavation becomes larger and larger,and the change rate of the top displacement first gradually decreases and then converges to a specific value.The smaller the support stiffness and pile-excavation distance,the greater the influence of rainfall duration on piles.The influence of rainfall duration on piles with different pile diameters is basically the same.The greater the excavation depth,the greater the influence of rainfall duration on piles.