考虑流变与固结效应的桩筏基础-地基共同作用分析

土的流变性与地基固结的综合作用，导致了上部结构与地基变形的时效性，并呈现出明显的非线性，对桩筏基础与地基共同作用的工作机理及其工作性能产生重要影响。为此，采用弹黏塑性流变模型考虑土的流变特性，通过有限元方法数值求解Biot耦合固结方程，对桩筏基础与地基共同作用的时间效应问题进行了非线性数值分析。通过算例计算，对加载后桩筏基础荷载分配和沉降特性及下覆土层中孔隙水压力的扩散和消散规律进行了探讨。研究表明，地基孔隙水压力的增长和消散不仅具有Mandel-Cryer效应，而且依赖于土的流变变形，尤其在排水条件较差时更为明显。因此，在分析桩筏基础内力变形的时效性时必须考虑土的流变性与地基的固结作用的联合效应。

Analysis of interaction of piled raft and foundation considering both effects of soil rheology and foundation consolidation

It has been clarified that the time-dependent behavior of soil results from both rheological properties of soft soils and consolidation of foundations which display a certain nonlinear characteristics and will play an important role in performance of major structures on soft soil grounds. In this paper, the time-dependent effects of soil deformation on interaction behavior of piled rafts and soil are considered. In the proposed procedure, the Biot’s fully coupled equations of consolidation are numerically solved by finite element method; and an elasto-viscoplastic (EVP) model of soils is employed to consider the rheology of soils. The variations with time and distribution in space of excess pore pressures in foundation soil underlying the piled raft and reactions as well as deformations or settlements of raft and piles during loading are examined through numerical analysis. It is shown that the coupled behaviour of rheology and consolidation of soils remarkably affect time-dependent performance of interaction of piled rafts and soils and the dissipation of excess pore pressures not only displays the Mandel-Cryer effects, but also is intimately associated with rheological deformation of ground especially in poor drainage condition. The pore-water pressure predicted considering rheological effect in addition to consolidation displays different patterns from those obtained by conventional consolidation analysis without consideration of soil rheology. While both effects of rheology and consolidation are taken account, the rigidity of piled raft plays a significant role in governing variation modes of reactions and deformations of piled raft with time. Furthermore, the edge pile displays different time-dependent behavior of internal forces and deformations from those of the central piles. The skin friction of pile may also display the nature of time-dependency. During loading, negative skin friction may occur in the pile segments near ground surface under soft soil condition and cannot be negligible in engineering design. The coupled analysis of rheology and consolidation gives rise a more rational evaluation of overall performance of interaction of piled raft and subsoil and conventional analyses which overlooks time-dependency of soil deformation may cause a certain inaccuracy in evaluation of interaction behavior and unreliability in design of structures on piled raft and foundation.