基于桩-土界面脱开效应及摩阻力增强效应影响的水平荷载作用下桩受力机理研究

Bearing mechanism of laterally loaded piles under separation effect and friction enhancement effect of pile-soil interface

为研究桩侧摩阻力和桩端阻力对水平受荷桩承载性能的影响,在考虑桩侧变法向土抗力作用的基础上分别提出桩-土界面的摩阻力增强效应模型与脱开效应模型。以此为基础,分别推导得出桩竖向侧摩阻力作用下单位长度桩身抗力矩的数值解与简化公式;在双曲线型的桩端阻力-位移模型及摩阻力增强效应基础上,进一步推导得到基底水平阻力与基底抗力矩的数值解和简化公式。并将单位长度桩身抗力矩、基底抗力矩以及基底水平阻力分别代入四弹簧Winkler地基梁模型,采用传递矩阵法得到桩身响应解。通过多组算例对比分析,不但验证了所建议的理论公式正确性,也证明了简化公式的适用性。参数影响分析结果表明:桩顶水平变形降低幅度随着柔性系数的增加、长径比的减小而提高;同时,随着柔性系数的减小,基底抗力矩和水平阻力对基桩水平承载特性的影响逐渐减弱,当为柔性桩时可忽略不计。

To investigate the influence of pile side friction and pile tip resistance on the bearing performance of laterally loaded piles, the calculation models considering separation effect and friction enhancement effect of pile-soil interface under the action of variable normal soil resistance along pile shaft was proposed. Based on the effects mentioned above, the numerical and simplified expressions of pile shaft resisting moment per unit length induced by vertical shaft resistance were deduced, respectively. Similarly, expressions of pile tip resisting moment and tip lateral resistance were obtained based on the hyperbolic model of pile tip resistance versus displacement and the friction enhancement effect. The shaft and tip resisting moment, as well as tip horizontal resistance, were substituted into the four-type Winkler spring model. The transfer matrix solution for pile responses was solved. Several case-study comparisons verified the correctness of the proposed theory and the applicability of the simplified expressions. The parametric study shows that the degradation of pile head horizontal deformation will increase as the flexibility coefficient increases or the aspect ratio reduces. Moreover, the influence of tip resisting moment and pile tip horizontal resistance on lateral bearing capacity will reduce as the flexibility coefficient decreases, which can be ignored for flexible pile.