基于PHC管桩现场静载试验的基桩承载特性研究

Research on bearing characteristics of foundation piles based on on-site static load tests of PHC pipe piles

【目的】我国沿海地区广泛存在饱和软土地层,且不同区域地层差异显著。软土前期固结预处理会使得地层的物理力学特性产生变化,为了准确计算后续施工中基桩的竖向承载力,最直接的办法就是通过现场竖向抗压静载试验实测得到桩侧摩阻力分布规律。【方法】在舟山某基地工程开展了5根桩的现场静载试验,桩1—桩4用于分析不同桩端持力层条件和桩径对PHC管桩单桩极限承载力的影响;通过在桩5桩身布设振弦式钢筋计,实时监测静载试验过程中桩身轴力,进而得到桩侧摩阻力的分布和变化规律。【结果】结果显示,桩1—桩4静载试验得到的极限承载力分别为8 000 kN、8 000 kN、6 600 kN和7 200 kN;实测分析得到桩5在处理后的两层淤泥质粉质黏土层中桩侧摩阻力分别为31 kPa和35 kPa。【结论】结果表明,实测得到的桩侧摩阻力大于勘察提供的建议值,说明地基预处理后桩土界面强度提高,计算得到的桩基承载力与静载试验测试值更加吻合;随着桩顶荷载的逐渐增大,桩身轴力也逐渐增大,且自上而下桩身轴力逐渐减小。研究成果为处理后深厚软基中桩基承载特性的计算提供试验依据。

[Objective]There are widely saturated soft soil in coastal areas of China and significant differences in strata between different regions.In addition,soft soil usually requires drainage consolidation pre-treatment,which can enhance the physical and mechanical parameters of the formation.In order to accurately calculate the vertical bearing capacity of the foundation piles for subsequent construction,[Methods]the most direct method is to obtain the distribution law of pile side friction through on-site vertical compressive static load tests.The on-site static load tests of 5 piles were carried out in the Zhoushan Base project.The static load tests of piles were carried to study the influence of different pile end bearing layer conditions and pile diameter on the ultimate bearing capacity of PHC pipe piles.Pile 5 is equipped with a vibrating and rotating steel bar gauge on the pile body.During the static load test process,the distribution and variation of pile axial force and pile side friction resistance can be monitored in real-time.[Results]The ultimate bearing capacity obtained from the static load test of piles 1~4 is 8 000 kN,8 000 kN,6 600 kN,and 7 200 kN,respectively.The actual measurement analysis shows that the pile side friction resistance in the muddy silty clay layer is 31kPa and 35kPa.[Conclusion]The measured pile side friction resistance is greater than the recommended value provided by the survey.This indicates that the strength of the pile soil interface increases after the foundation pre-treatment.The calculated pile foundation bearing capacity is more consistent with the static load test values.As the load on the pile top increases,the axial force of the pile body gradually increases,and the axial force of the pile from the top to the bottom gradually decreases.The research result provide experimental basis for the study of pile foundation bearing mechanism and calculation of bearing capacity.