考虑地基土非线性固结的桩侧负摩阻力计算方法研究

针对软土地基因固结沉降在桩侧引发的负摩阻力问题,从桩土相互作用机理出发,首先,根据软土压缩曲线性质,采用双曲线应力应变模型考虑地基土固结非线性特性,推导了桩侧土沉降随深度和时间变化的计算公式;其次,引入Gibson地基理论考虑地基土的非均质性,结合桩土界面剪应力–剪应变双曲线模型,建立了反映桩土界面剪切刚度系数随深度非线性增长的荷载传递函数。在此基础上,联立桩体平衡方程,获得了桩侧摩阻力、桩身轴力分布和中性点位置。最后,将理论计算曲线与工程实测曲线进行对比,并进一步分析了压缩试验参数、固结度、桩径及桩长、地表堆载对桩侧负摩阻力及中性点位置的影响,结果表明计算方法是可行的,可为类似工程提供参考。

Negative skin friction of piles considering nonlinear consolidation of soil

The objective of this study is to discuss the widespread problem of negative skin friction in soft soil foundation based on pile-soil interaction. According to the characteristics of soft soil compression curve, the hyperbolic consolidation theory is adopted to reflect the nonlinear response of soil consolidation, and the derivation of soil subsiding with depth as well as time is also achieved. Moreover, the Gibson theory is introduced to consider the heterogeneity of soil by combining the shear strain for pile-soil interface with a hyperbolic model of shear stress, and a load transfer function is established, indicating that it can reflect the characteristics of nonlinear increase with depth for the initial shear stiffness between the pile and soil. On this basis, the pile skin friction, pile axial force and the position of neutral point are obtained by an iterative method. In addition, field tests are used to verify the proposed method and the influences of the factors such as parameters of compression test, soil consolidation degree, pile diameter, pile length as well as surcharge on negative skin friction and position of neutral point. The comparative results indicate that the proposed method is feasible in the practice.