考虑负摩阻力的刚性桩复合地基中性面深度及桩土应力比计算

研究了刚性桩复合地基桩侧摩阻力在线性模式下中性面深度及桩土应力比的计算方法。根据刚性桩复合地基各组成部分的沉降变形关系,推导了垫层–桩–土的变形协调方程。考虑负摩阻力对桩土工作性状的影响,将桩侧摩阻力分布由试验曲线简化为线性模式,同时考虑桩顶刺入褥垫层,桩底刺入下卧层,结合桩土变形协调方程推导了中性面深度、桩顶平面桩土应力比、中性面桩土应力比的计算公式。分析了多种因素对中性面深度及桩土应力比的影响,结果表明:刚性桩复合地基的中性面深度比在0.15~0.35之间,中性面桩土应力比相比桩顶平面桩土应力比增大10%~40%。最后应用于某工程现场载荷试验和某刚性桩复合地基模型试验,计算值与试验值吻合较好。

Calculation of neutral surface depth and pile-soil stress ratio of rigid pile composite foundation considering influence of negative friction

The computing method for determining the neutral surface depth and pile-soil stress ratio of rigid pile composite foundation is studied under skin friction of pile using a linear model. A cushion-pile-soil deformation compatibility equation is derived based on the settlement deformation relationship among different constituent parts of rigid pile composite foundation. The distribution of the skin friction is simplified from a test curve to a linear model by taking into account the influence of negative friction on working properties of the pile and soil. Additionally, considering the top of the pile piercing into the cushion and the bottom of the pile into the substratum, and using the cushion-pile-soil deformation compatibility equation, a model is created to describe the neutral surface depth and pile-soil stress ratios on the top surface and neutral surface of the pile. Using the proposed method, the effects of various factors on the neutral surface depth and pile-soil stress ratio are analyzed. The results show that the neutral surface depth ratio of the rigid pile composite foundation is within 0.15~0.35, and that the pile-soil stress ratio on the neutral surface of the pile increases by 10%~40% of the top plane of the pile. Finally, the proposed method is applied to an engineering field test and a rigid pile composite foundation model test, and the calculated values are consistent with the experimental ones.