竖向荷载下带帽有孔管桩复合地基工作性状试验研究

The composite foundation of rigid pile with cap has been applied widely in the deep soft soil treatment of the highway and high-speed railway, etc., and has already become the magistral method for the deep soft soil treatment. In order to alleviate the adverse effects of the squeezing effect and excess pore water pressure dissipation in the process of the static sinking pile, the scheme of using pipe-pile with hole substituting for the ordinary tubular pile has been put forward.The key problems of the pipe-pile with hole design, the squeezing effect, excess pore pressure dissipation, ultimate bearing capacity of pipe-pile with hole,the load-transfer proberty of the composite foundation of pipe-pile with cap and hole, and group piles effect have been studied scientificly in this research by the method of model test and numerical simulation. The design method and producting process of pipe-pile with hole, and the method of pile sinking have been studied in the inside model test.The sqeezing effect and excess pore pressure dissipation have been researched during pile sinking. The working-properties of pile-soil interaction, load-transfer, settlement deformation and group piles effect of the composite foundation of pipe-pile with cap and hole under vertical loads have also been discussed. The main effect factors have been researched on the working-properties of the composite foundation of pipe-pile with cap and hole, the sensitivity analysis of it has been analyzed. At last,the working-properties of the composite foundation of pipe-pile with cap and hole under vertical loads have been revealed,and the research aim has been fully achieved.The results can provide the theoretical and experimental support for the wide application of the composite foundation of pipe-pile with cap and hole.

带帽刚性桩复合地基广泛应用于高速公路、高速铁路等深厚软基处理工程，逐渐成为一种主导的软基处理方式。为减轻静压沉桩挤土效应和超孔隙水压力的不利影响，提出用有孔管桩替代常规无孔管桩方案。本项目紧紧围绕有孔管桩设计、静压沉桩过程中挤土效应与超孔隙水压力消散、有孔管桩极限承载力、带帽有孔管桩复合地基荷载传递特性与群桩效应等关键的科学问题，采用室内模型试验和数值模拟试验相结合的方法，研究有孔管桩设计、制作工艺和室内静压沉桩方法，研究有孔管桩在静压沉桩过程中的挤土效应和超孔隙水压力消散规律，研究竖向荷载下带帽有孔管桩复合地基桩土相互作用、荷载传递、沉降变形及群桩效应等工作性状，研究带帽有孔管桩复合地基工作性状的主要影响因素，并对其进行敏感性分析，达到揭示竖向荷载下带帽有孔管桩复合地基工作性状的目的，为带帽有孔管桩复合地基技术应用推广及其理论研究提供试验基础。

带帽刚性桩复合地基广泛应用于高速公路、高速铁路等深厚软基处理工程，逐渐成为一种主导的软基处理方式。为减轻静压沉桩挤土效应和超孔隙水压力的不利影响，提出用有孔管桩替代常规无孔管桩方案。本项目紧紧围绕有孔管桩设计、静压沉桩过程中挤土效应与超孔隙水压力消散、有孔管桩极限承载力、带帽有孔管桩复合地基荷载传递特性与群桩效应等关键的科学问题，采用室内模型试验和数值模拟试验相结合的方法，研究有孔管桩设计、制作工艺和室内静压沉桩方法，研究有孔管桩在静压沉桩过程中的挤土效应和超孔隙水压力消散规律，研究竖向荷载下带帽有孔管桩复合地基桩土相互作用、荷载传递、沉降变形及群桩效应等工作性状。研究发现：（1）在静压沉桩过程中，有孔管桩能够在一定程度上降低桩周土体中超孔隙水压力的峰值，加快超孔隙水压力的消散。通过对星状对穿有孔管桩和无孔管桩桩周不同位置的超孔压比进行对比分析，得到星状对穿有孔管桩对周围建筑环境的影响范围约为8.9D，无孔管桩对周围建筑物环境的影响范围约为10.3D。这说明有孔管桩能够在一定程度上降低桩周土体中超孔隙水压力的最大值，加速超孔隙水压力的消散。（2）在单桩静载荷载试验中，单桩静荷载Q-s关系曲线中，各桩的桩顶沉降量及其回弹量，随无孔管桩、单向对穿有孔管桩、星状有孔管桩、双向对穿有孔管桩等桩型改变，在数值上依次减小。桩身开孔能有效地减小桩顶沉降量和桩顶沉降的回弹量。四种管桩的桩侧摩阻力呈腰部鼓起状态分布，桩侧摩阻力最大值发生在管桩的中腰部位，桩侧摩阻力随着桩顶施加竖向荷载的增加而增大。从桩体极限承载力和桩身轴力的折减率来看，星状有孔管桩均为最小。（3）在带帽有孔管桩复合地基静载荷载试验中，带帽有孔管桩复合地基总沉降小于带帽无孔管桩复合地基，且沉降曲线较为平缓；带帽有孔管桩桩身轴力小于带帽无孔管桩；带帽有孔管桩复合地基桩帽间土体表面土压力较大；带帽有孔管桩复合地基桩侧摩阻力大于带帽无孔管桩复合地基；带帽有孔管桩复合地基桩土应力比小于带帽无孔管桩复合地基。试验结果验证了桩身开孔能让超孔隙水主动进入管桩内腔，降低土体含水量，提高土体抗剪强度，使带帽有孔管桩复合地基更有利于发挥桩周土体分担荷载的作用，从而减小复合地基总沉降，提高复合地基承载力。通过本项目研究，达到揭示竖向荷载下带帽有孔管桩复合地基工作性状的目的，为带帽有孔管桩复合地基技术应用推广及其理论研究提供试验基础。