基于塑性极限理论的上限分析法，借鉴已有数值分析和室内模型试验所揭示的带帽刚性桩破坏模式，构建了其运动许可速度场，并引入统一强度理论，根据能量平衡原理，推导了能考虑中主应力影响的带帽刚性桩极限承载力上限计算公式。同时通过参数分析，得到了带帽刚性桩极限承载力随桩帽尺寸、土的黏聚力和内摩擦角的变化规律。研究发现：考虑中主应力影响的带帽刚性桩的上限解较不考虑时有较大的提高，对于带帽刚性桩承载力计算时，实际统一强度理论中反映中主应力影响的参数取0.1～0.2附近较为合理。带帽刚性桩承载力随着桩帽尺寸的增大而增大，且桩帽直径与桩径之比 时，承载力增大趋势较为明显；承载力随着土体黏聚力和内摩擦角的增大而增大。通过与已有理论方法和试验结果对比分析发现，本文提出的方法不仅在理论上更严密，而且可得到更符合实际的计算结果。

Based on the upper plastic limit analysis theory, the kinematically admissible velocity field of a capped rigid pile is obtained through both numerical and model tests. According to the energy balance principle and unified strength theory, an equation is developed for the ultimate bearing capacity limit solution of the pile, in which the effect of the intermediate principal stress is considered. In addition, the variations of the pile ultimate bearing capacity with the cap size, soil cohesion and internal friction angle are analyzed through parametric analysis. It is found that the upper limit solution increases more significantly for the pile with considering the intermediate principal stress than those without. A reasonable range of the unified strength parameter is from 0.1 to 0.2 in calculating the rigid piles bearing capacity. With the increase of the cap size, the pile bearing capacity increases. When the ratio of cap diameter D to pile diameter d is greater than 2, the bearing capacity increases more significantly. With the increase of soil cohesion and internal friction angle, the bearing capacity increases drastically. By comparison with experimental results, it is found that the proposed method yields better results than the existing theoretical methods.