基桩在施工和使用过程中易产生缩颈缺陷，极大降低其承载能力，给上部结构造成安全隐患，桩土相互作用则是桩承载能力的关键所在。本项目拟利用透明土模型试验、数值模拟和理论分析方法，研究不同荷载下不同类型的缩颈桩桩土相互作用规律及其可靠度的变化规律。具体研究内容为：首先，采用熔融石英砂作为固体颗粒，并辅以与其具有相同折射率的孔隙溶液配置透明砂土，研发与之配套缩颈桩的透明土模型试验加装装置；然后，进行基于透明土技术的缩颈桩模型试验，研究透明土中缩颈桩在不同荷载作用下土体内部变形的发展规律；分析桩端和桩侧土体中颗粒的细观运动形态；揭示缩颈缺陷处、完整桩身与土颗粒之间的相互作用。同时，采用有限元及离散元的方法对不同荷载下不同类型的缩颈桩桩-土相互作用进行数值模拟，并与试验结果进行对比分析。最后，利用承载力折减系数和蒙特卡洛模拟法研究缩颈参数对承载力可靠度指标影响规律，进而确定不同条件下目标可靠度指标。

Pile foundation is prone to shrinkage defects during construction and use, which greatly reduces its bearing capacity and poses a safety hazard to the superstructure. Pile-soil interaction is the key to its bearing capacity. This project intends to use the transparent soil model test, numerical simulation and theoretical analysis method to study the interaction law of different types of constricted piles and soils under different loads and the variation of reliability index. The specific research contents are as follows: Firstly, the fused silica sand is used as the solid particles, the pore solution with the same refractive index is used as the transparent sand, and the transparent soil model test installation device with the shrinkage defect pile is developed. Secondly，the model test of shrinkage defects piles based on transparent soil technology was carried out to study the development law of internal deformation of soil-concave piles in transparent soil under different loads. The meso-motion morphology of particles in pile-end and pile-side soils was analyzed. Explain the interaction between the shrinkage defect, the intact pile and the soil particles. At the same time, the finite element method and discrete element method are used to simulate the pile-soil interaction of different types of shrinkage defects piles under different loads, and compared with the test results. Finally, the bearing capacity reduction coefficient and Monte Carlo simulation method are used to study the influence law of the shrinkage parameters on bearing capacity reliability index, and then the target reliability index under different conditions is determined.