均质土层中超长两桩基础承载性状的数值研究

Numerical study on behavior of super-long two-pile foundation in homogeneous soil

基于三维有限元分析方法,研究了均质地基土中超长两桩基础的承载性状。在有限元模型建立中,为了考虑桩–土共同作用,桩和地基土均用8结点等参单元模拟;为了考虑桩–土间的变形非线性特性,桩–土间设置了一层有厚度的薄单元;桩身混凝土的应力应变关系用线弹性模型模拟,地基土用Duncan-Chang非线性弹性模型模拟,桩周薄单元用河海大学薄单元模型模拟。计算分析表明,基桩的竖向刚度随桩中心距的增大、桩长的增大而增大,但其总小于单桩的竖向刚度;桩侧阻端阻综合群桩效应系数随桩顶沉降、桩中心距的增大而增大,随桩长的增大呈先减小后增大或基本保持不变的变化特点。

Based on the three-dimensional finite element method （3D FEM）, the behavior of super-long two-pile foundation in homogeneous soil was investigated. During the course of establishing the finite element model, both the piles and soil were simulated using 8-node isoparametric elements in order to consider the co-action of the piles and soil, and a layer of thin element was placed along the side surface of the piles in order to consider the possible nonlinear deformation between the piles and soil. The relationship between stress and strain of concrete around the piles was simulated using a linear elastic model, that of the foundation soil was simulated using a nonlinear elastic model suggested by Duncan ＆ Chang, and that of the special thin element was simulated by a special model suggested by Hohai University of China. The computed results indicated that the vertical stiffness of the piles in the super-long two-pile foundation increased with the increase of the distance between the two piles or the length of the piles, but the stiffness was always less than that of single super-long pile. The coefficient of two-pile foundation effect defined by the combination of critical tip resistance and side resistance of the piles was also investigated. The coefficient increased with the increase of the settlement at pile top or the distance between the two piles. But with the increase of the pile length, the coefficient first decreased and then increased or was almost invariant.