分别采用LadeDuncan模型和刚塑性薄单元模型模拟土体的弹塑性和桩土界面的相对运动 ,对竖向受荷群桩进行了三维弹塑性有限元分析。研究表明：大、小桩距群桩的承载性状有 明 显差异,大桩距群桩侧摩阻力存在"沉降软化"现象,不同于小桩距群桩的"沉降硬化"；增 大桩距有利于调动台底土参与工作,提高承台分担比；随荷载增大,各桩荷载趋于均匀分布。

 3D elasticoplastic finite element method was used to analyse the beha vior of vertically loaded pile groups by using LadeDuncan model and stiffplasti c th in unit model respectively,to simulate elasticoplastic soil body and the relat iv e movement between piles and the surrounding soil.The analytic results showed th at the obvious differences of the loadbearing characteristics of pile groups e xist for large or small pile spacings,i.e.,the surrounding friction resistance o f pile group with large pile spacing occurs "settling softening" phenomenon,whi ch is different from "settling hardening" of those with small pile spacing; To increase pile spacing is benificial to transferring load to soil under the supp orting platform and thus can increase the ratio of platform′s load to total loa d;With the increase of load,the differences of reaction on pile tops decrease,an d the distribution of total load on group piles trends towards approximately unif orm.