砂土中等截面桩的上拔机制分析

Analysis of uplift mechanism of uniform section piles in sandy soil

桩的上拔承载性能的宏观力学现象与桩周土细观结构变化相关,应用细观力学的颗粒流(PFC2D)数值模拟方法对承受上拔荷载作用的桩基进行了分析,数值模拟了上拔荷载作用的桩及桩周土的细观力学特征,研究了桩侧摩阻力的分布、桩周土剪切带的形成过程,较好的再现了桩的荷载-位移关系的实验结果,并与宏观物理实物试验的位移实测结果作了对比分析。分析了土体中剪切带形成过程中的颗粒间的细观变化及其形成过程,当上拔荷载达到极限时,上拔桩的剪切带形成原因是密砂的应变软化效应;颗粒流数值模拟的颗粒接触力与实物物理试验桩侧摩阻力是同一的,数值模拟的荷载-位移曲线与实物物理试验的荷载-位移曲线一致;桩侧摩阻力、桩上拔过程中剪切带的形成过程、桩上拔荷载-位移关系与颗粒流数值模拟的颗粒分布、速度、接触力的细观参数的变化密切相关。桩承受荷载过程中土颗粒细观结构变化的颗粒流仿真,是关于细观力学特征与宏观力学响应的初步研究。

The macro-mechanics phenomena of piles on uplift loading are closely related to the changes of its meso-mechanics.Piles on uplift loading are analysed with PFC2D(Particle Flow Code in 2 Dimensions) numerical simulation of meso-mechanics.PFC2D is used to simulate numerically the character of meso-mechanics on soil,to study the uplifting displacements of pile,the distribution and velocity of sand particle,the surface of rupture in soil and to compare with the results of material object tests.Not only did PFC preferably reproduce the relationship of uplift loading and displacement of pile experiment but also suitably simulate pile、s gradually progressive failure pattern.The changes in the meso-syructure and the forming process on the shear zone of soil body have been analyzed.The cause of forming uplift pile shear zone is strain softening effect of the dense sand.Particle contact force of PFC2D numerical simulation and pile side frictional resistance of physical tests are identical.The load-displacement curves are consistent with the results of numerical simulation and physical tests.It is closely related to pile side frictional resistance,the forming process of shear zone,the load-displacement and particles distribution,particles speed,particle contact force of PFC2D numerical simulation.Changes of soil particle meso-structure and displacement of piles of PFC2D numerical simulation are initial study of meso-mechanics character and macro-mechanics response.