典型软土层中群桩变刚度调平设计方案研究

Design scheme of variable stiffness leveling of pile group in typical soft soil stratum

群桩等刚度设计中因“加筋遮帘效应”会导致各基桩间轴向内力出现差异,造成上部结构开裂、倾斜,严重影响上部建筑结构的安全和使用。为减小群桩各基桩间轴向内力差,通过开展群桩变刚度调平优化设计研究,以进一步提高群桩的承载性能。基于变刚度调平设计理念,采用三维有限元分析软件ABAQUS对竖向受荷群桩的沉降特性及基桩轴向内力分布特征进行分析。重点选取粉质黏土、砂层土和淤泥质土等典型软弱土层,通过改变桩长、桩径和桩间距3个关键参数的调节方式以调平基桩刚度,使基桩轴向内力分配均衡化,据此提出3种典型土层中基桩变刚度调节优化设计方案。研究结果表明:粉质黏土、砂层土和淤泥质土中,各基桩轴向内力差异与中心桩内力值比例分别高达90.5%,51.3%和51.8%,且不同调节方式对不同土层中基桩刚度调节效果影响程度不同;3种典型土层中,变桩长、桩径的方式可显著降低各基桩间内力差值,但淤泥质土和砂层土中变桩间距对降低内力差的效果较小。不同土层中基桩刚度调节效果影响程度的不同与土层力学特性、桩土相互作用和荷载承担比例直接相关,故群桩变刚度调平设计应针对不同典型桩侧土层组合采取合适的调节方式。

In the stiffness design of pile groups,the“reinforced curtain effect”will lead to the difference of axial internal force between foundation piles,resulting in the cracking and inclination of the superstructure.This will seriously affect the safety and use of the superstructure.In order to reduce the axial internal force difference between the foundation piles of pile group,the variable stiffness leveling optimization design of pile group was carried out to further improve the bearing performance of pile group.Based on the variable stiffness leveling design concept,the settlement characteristics of vertically loaded pile groups and the axial internal force distribution characteristics of foundation piles were analyzed by using the three-dimensional finite element analysis software ABAQUS.The typical soft soil layers,such as silty clay,sandy soil and muddy soil,were selected to level the stiffness of the foundation pile by changing the adjustment mode of three key parameters(pile length,pile diameter and pile spacing),so as to balance the distribution of axial internal force of the foundation pile.The results show that in silty clay,sandy soil and muddy soil,the ratio of the axial internal force difference of each pile to the internal force value of the central pile is as high as 90.5%,51.3%and 51.8%respectively.The different adjustment methods have different effects on the adjustment effect of pile stiffness in different soil layers.In the three typical soil layers,the method of changing pile length and pile diameter can significantly reduce the internal force difference between foundation piles,but the effect of changing pile spacing in muddy soil and sandy soil is small.The influence degree of pile stiffness adjustment effect in different soil layers is directly related to the mechanical characteristics of soil layer,pile-soil interaction and load bearing ratio.Therefore,the variable stiffness leveling design of pile group should adopt appropriate adjustment methods for different typical pile side soil layer combinations.Finally,the optimal design scheme of variable stiffness adjustment of foundation pile in three typical soil layers is given.