基于隔时复压试验的静压桩承载力时效性研究

Time effect of bearing capacity of jacked pile based on interval re-pressed test

静压桩沉桩结束后,其承载力随时间而变化,对桩承载力的时效性研究可为静压桩设计及施工提供参考。文章以山东省潍坊市滨海经济开发区滨湖苑小区工程现场为试验场地,通过两根静压桩进行的隔时复压试验的实测数据,研究了广义极限承载力与最终压桩力的关系、桩端阻力和侧摩阻力随时间变化规律,提出了静压桩承载力三阶段增长模型。结果表明:广义极限承载力不同于最终压桩力,其提高主要是在沉桩结束的9 d内;在沉桩结束后20 h时,桩端阻力和桩侧摩阻力对桩承载力的贡献各为50%,出现"贡献平衡点",压桩结束13 d后变为侧摩阻力主要起承载作用,出现"侧阻绝对硬化"和"端阻相对软化"现象;不同的土层提供不同的桩侧摩阻力,粉质粘土最大,砂质粉土和粉土次之,淤泥质土最小;静压桩承载力增长模型由三阶段组成,桩端阻力的增长仅发生在第一阶段,桩侧摩阻力的大幅度增长集中在第一、二阶段,在第三阶段略有提高。

The bearing capacity of jacked pile varies with timeafter the end of pile jacking, and the study on the time effect of bearing capacity of jacked pile has some implications for the design and construction of jacked pile. This paper, by taking the project Binhuyuan Community, Binhai economic development zone, Weifang City, Shandong Province as the test site, compares the measured data of two piles, studies the relationship between the general ultimate bearing capacity and ultimate compressive strength, and the growth law of tip resistance and shaft resistance, and also proposes the bearing capacity of jacked pile increase model in three stages. The results show that, the general ultimate bearing capacity is different from the ultimate pile load, which increases mainly in the 9 days after the end of pile jacking, and grows faster in the initial stage than the later stage. At 20 hours after the end of pile jacking, the contribution of tip resistance and shaft resistance to bearing capacity of pile is the same, 50 percent respectively, called ＂ contribution balance point ＂ The increase of ultimate bearing capacity of the jacked pile is mainly determined by shaft resistance on 13 days after the end of pile jacking, ＂absolute hardening of shaft resistance＂ and ＂relative softening of tip resistance＂ occurred. Different soil layers provide different shaft resistance, the silty clay is the largest, sandy silt and silty soil are the second, and the silt soil is the smallest. The static pressure pile bearing capacity growth model is composed of three stages, the increase of the pile end resistance is only in the first stage, the large increase of the pile side friction resistance is concentrated in the first and the two stage, and slightly increases in the third stage.