软土蠕变特性的多尺度耦合试验与机理分析

Creep is a time dependent deformation characteristic, which has an important influence on the settlement of soft soil foundation but it’s mechanism is not yet clear. In order to deeply understand the creep mechanism of soft soil, the project takes the Pearl River Delta soft soil as the research object, and conducts multi-scale coupled experiments and theoretical analysis of its creep characteristics at the macro-microscopic level. The research work includes the following aspects. Firstly, based on the material composition and microstructure test of soft soil, the material and structural factors that can determine the creep properties of soft soil are analyzed. Secondly, by testing the microstructure of the original sample and the remodeling sample during the whole creep process, the particle and pore change parameters can be extracted, and the structural unit body and the pore quantitative index analysis system can also be established so that the evolution law of the micro structure of soft soil is analyzed in the whole process of creep. Thirdly, through studying the correlation and correspondence between creep characteristics and load factors, material composition, microstructure characteristics and pore characteristics, the key micro parameters affecting creep deformation are analyzed, the quantitative relationship between the corresponding microscopic parameters and creep properties is established, the mechanical behavior mechanism of soft soil contained in the variation law of micro parameters is revealed, and the cross scale correlation between micro parameters and macroscopic performance is realized. The research results of the project is of great significance to explore the relationship between the deformation and time of soft soil and the stability of buildings built on soft soil foundations, and can also provide theoretical support for the development of new technologies for soft ground treatment.

蠕变是一种与时间相关的变形特性，对软土地基的沉降有着重要影响，但其蠕变机理尚不明确。为深入了解软土蠕变机理，本项目以珠三角软土为研究对象，对其蠕变特性进行宏-微细观层次的多尺度耦合试验与理论分析。首先基于软土物质组成及显微结构试验，分析决定软土蠕变特性的物质因素和结构性因素；测试蠕变全过程原状样及重塑样的微观结构，提取颗粒与孔隙变化参数，建立软土微结构演化规律量化分析体系，分析软土微细观结构在蠕变全过程的演化规律；研究软土蠕变特性与荷载因素、物质组成、微结构特征及孔隙特征的关联性及对应性，分析影响蠕变变形的关键微细观参数，建立相应微细观参数与蠕变特性的定量化关系，揭示蕴含在微细观参数变化规律中的软土力学行为机理，实现微细观参数与宏观表现的跨尺度关联。项目研究成果对探讨软土变形与时间关系以及建于软土地基上建筑物的稳定性有重要意义，也可为软基处理新技术的发展提供理论支撑。

珠江三角洲主要由东江、北江和西江在湾内堆积而成，在经历了复杂的海侵、海退与江水的共同作用形成了三角洲基本形态。由于珠江口区受到滨海浪流及潮汐力的综合作用，大量泥砂物质逐渐在湾内淤积，以及后期的生物作用和化学作用，形成了分布广泛的海积软土层，具有“三高两低一长”的特点，且在层理特征和物理力学性质上与其它沉积相软土层之间存在明显差异特征，如土层的均匀性极差、平面分布不规则、与粉细砂层呈互层状产出等。软土具有显著的蠕变特性，越来越多的工程实践和调查研究表明，如果在实际工程应用中忽略土体变形时间效应的影响，则会产生诸多问题，轻则影响正常使用，重则造成极大的安全隐患和重大经济损失。1）软土物质组成及显微结构试验与因素分析：采集珠三角典型的天然原状软土，明确该地区软土成分、结合水含量、易溶盐含量、pH值、阳离子交换、颗粒比表面积、显微结构形成及变化机制等区域特征。2）软土蠕变全过程微细观结构演化观测与特征分析：在不同蠕变试验条件下，主要从结构联结特征及孔隙分布特征等方面出发，选取蠕变前、蠕变中、蠕变后及破坏后等多个时间点的原状样及重塑样并利用微观定量技术进行微观结构测试，提取了颗粒与孔隙变化参数，建立软土微结构演化规律量化分析体系，研究在不同荷载组合下颗粒特征与微细观结构要素等定量化参数及各种分维值不同阶段的变化特征；并基于土体微结构和孔隙的分形特征，引入分形几何学的相关理论进行非确定结构参数的确定，研究软土微细观结构在蠕变全过程的演化规律。3）软土蠕变特性的宏微观物理机制分析：基于试验结果及微细观结构特征变化规律分析，研究珠三角软土蠕变特性与荷载因素、物质组成、微结构特征及孔隙特征的关联性及对应性，分析影响软土蠕变变形的关键微细观参数。项目研究成果对探讨软土变形与时间关系以及建于软土地基上建筑物的稳定性有重要意义，也可为软基处理新技术的发展提供理论支撑。