等截面桩与扩底桩抗拔承载特性数值分析研究

建市了等截面桩与扩底桩的抗拔分析模型。采用直接约束处理的接触算法与库仑摩擦模型来模拟桩-土界面，土体选用抛物线型Mohr-Coulomb本构模型。通过程序的二次开发，实现初始应力场的合理计算，并采用位移边界对扩底抗拔桩的上拔过程进行动态的非线性有限元模拟。以现场足尺试验中的试桩为数值分析对象，通过调整计算参数使计算得到荷载-位移关系曲线与试验结果接近，来验证数值模型的正确性并确定计算参数。在此基础上，研究了上拔过程中轴力、侧摩阻力的火小与分布、桩身与扩大头附近土体变形与塑性区的发展规律。数值分析加深了对扩底桩抗拔承载特性的进一步认识。

Numerical modeling of uplift behavior of normal piles with straight shaft and pedestal piles

Numerical modeling was used to analyze the uplift behavior of normal piles with straight shaft and pedestal piles. The contact problem between pile and soil was solved by direct constraint method. In this procedure, the motion of the bodies is tracked, and when contact occurs, direct constraints are placed on the motion using boundary conditions-both kinematic constraints on transformed degrees of freedom and nodal forces. The Coulomb friction model was used to treat skin friction force of pile shaft. Soil were modeled as parabolic Mohr-Coulomb material. Reasonable initial stress was obtained by using subroutines. The dynamic nonlinear modeling of uplift procedure was done by applying displacement boundary condition on pile top. The result of in-situ full-scale pile test was used to verify the parameter for computation. Then the distribution law of axial force, friction force, displacement and plastic zone of soil around enlarged base were studied.