基桩在施工和使用过程中易产生缩颈，给上部结构带来安全隐患。厘清带承台缩颈单桩水平承载特性，对工程设计及桩基加固修补具有指导意义。本文采用熔融石英砂和折射率相同的孔隙液配制透明砂土，开展带承台完整桩和缩颈桩透明土模型加载试验，研究缩颈对水平极限承载力的影响规律；然后利用Mat-PIV增量程序处理加载前后土体颗粒散斑场，得到桩周土体变形规律；结合三维有限元数值仿真揭示缩颈改变带承台单桩水平承载特性的原因。结果表明：缩颈削弱了水平荷载沿桩身的传递能力，增大桩身上部变形和桩侧土反力。缩颈位置距桩顶越近或缩颈尺寸越大，基桩水平极限承载力损失越严重。桩身弯曲会使承台在加载侧发生斜向下位移，对土体产生竖向压力，从而提升浅部土体强度并产生摩擦力约束基桩变形，增强基桩的承载性能。

Pile foundation is easy to develop necking during construction and service, which will bring potential safety hazards to the superstructure. Clarifying the characteristic of horizontal bearing capacity for necking pile with cap is important to engineering design and reinforcement repair of pile foundation. Transparent soil made by fused silica sand and pore liquid with the same refractive index is utilized to carry out model experiment and investigate the effect of necking on horizontal bearing capacity of necking pile with cap. The soil deformation around piles were obtained after process the soil particle speckle field assisted with Mat-PIV incremental program. Subsequently, three-dimensional finite element numerical simulation is incorporated to explain the change reason of horizontal bearing capacity induced by necking. Results show that necking will weaken the transfer ability of horizontal load along pile shaft, and drive the deformation of upper pile shaft and soil anti-force on pile side to increase. The horizontal bearing capacity decreases with the increase of necking dimension, or decrease of necking position away from pile top. The pile bending can cause pile cap to develop oblique downward displacement, which will exert vertical pressure on the soil. Subsequently, the strength of the shallow soil is enhanced and the developing friction limit pile deformation, resulting in improving the bearing capacity of the pile.

TU473.1

国家自然科学基金(51978247)；河南省高等学校青年骨干教师培养项目(2021GGJS058)