粗粒土中预制桩的静压施工残余应力  

Post-installation residual stresses in preformed piles jacked into granular soils

作　　者：俞峰 谭国焕[2] 杨峻[2] 李启光[2] 

机构地区：[1]浙江理上大学建筑工程学院,浙江杭州310018 [2]香港大学土木工程系,中国香港

出　　处：《岩土工程学报》2011年第10期1526-1536,共11页Chinese Journal of Geotechnical Engineering

基　　金：浙江省自然科学基金项目(Y1090610);住建部科学技术项目(2011-K3-34)

摘　　要：预制桩沉桩施工阶段形成的桩身残余应力对桩的工作性状有重要影响。原位观测了两根H型钢桩静力压入粗粒土地基过程中的桩身应力,测得了很大的桩身与桩端施工残余应力。施工残余摩阻力之中性点深度随贯入桩长增加而下移,但两者之比值趋于定值。桩端残余应力除了与弹性系数有关,还受到压桩力与贯入速率的影响。随着压桩荷载循环次数的增长,残余负摩阻力不断累积,但某一固定土层深度的单位残余负摩阻力却呈现下降趋势,这与沉桩侧摩阻力的疲劳退化机理是一致的。施工残余应力的存在改变了桩周土与桩端土的初始应力状态,使得桩–土体系在工作条件下会沿着与预期不一致的应力路径受荷至破坏。这对传统的静载荷试验和Osterberg试桩的成果分析方法提出了挑战。若考虑施工残余应力,对桩的抗拔承载性状有利,并使得开口管桩土塞效应问题变得更复杂。桩身残余应力的分布可基于残余摩阻力的折线型分布假定,利用桩端残余应力来预测。The working performance of a preformed pile may be significantly affected by the residual pile stress generated in the pile installation process.A field-test program is conducted in this study to investigate the load transfer behavior of two instrumented steel H-piles jacked into granular deposits during installation.Significant post-installation residual stresses are found to be locked in the test piles.The depth of neutral point for the residual shaft friction increases with increasing pile penetration but their ratios tend to be an invariable.Besides the well-known elasticity coefficient,the factors affecting the residual point resistance include the jacking force and the penetration rate.The average residual negative friction accumulates as the number of jacking strokes increases.Nevertheless,the unit residual negative friction at a given horizon shows a trend of degradation,which can be attributed to the presence of friction fatigue during pile installation.The residual pile stress is responsible for the variation in the stress state of the soils surrounding the pile shaft and beneath the pile base prior to loading service.This indicates that the pile-soil system will follow an unanticipated stress path toward axial loading failure.The data interpretation methods routinely adopted in the static and O-cell loading tests are going to be challenged in case that the influence of post-installation residual stress is involved.Also,the post-installation residual stress imposes positive effect on the uplift capacity of pile and increases the complexity of the plugging behavior of open-ended pipe piles.Assuming that the distribution of residual shaft friction resembles a folded line,a semi-empirical framework is proposed to estimate the residual pile stress at any depth from the knowledge of residual point resistance.

关 键 词：预制桩 施工效应 原位试验 残余应力 中性点 承载力 

分 类 号：TU473.1[建筑科学—结构工程]