结合水对软粘土力学行为的控制作用与机理

It is universally acknowledged that bound water plays an important controlling role in mechanical behavior of soft clay according to the previous researches. However, the mechanism of that controlling action is not yet fully known, the relationship between bound water and deformation and strength characteristics of soft clay has not yet carried out. Based on the previous researches and theories of engineering geology, theory of soil behavior, soil mechanics and clay mineralogy, this research adopt a new approach of "field investigation - laboratory test - mechanism exploration - model construction - analysis and evaluation". By this method, to combine with advanced test technologies, nonlinear analysis and numerical simulation by particle flow code, the bound water characteristics and the correlation between bound water and mechanical behavior for several kind of typical soft clay in both coastal and inland regions will be studied. Main contents of this research include interaction mechanism between bound water and soil particles, definition and characterization of bound water of different type, relationship between bound water and basic mechanical properties, creep-consolidation process and long-strength of soft clay, mathematical model of quantitative relationship between bound water and deformation and strength of soft clay. The objective of all these tests and studies is to understand the essence of deformation and strength for soft clay, get more-refined mathematical model of deformation and strength of soft clay, enrich the theory of soil mechanics, and finally provide a scientific theory basis for property improvement of soft soil and design of soft foundation.

结合水对软粘土的力学行为具有控制作用。已有成果表明，这种控制作用的机制尚未明确，结合水性质与软粘土变形与强度特性之间的关系研究尚未真正开展起来。课题拟在前人研究成果的基础上，以工程地质学、土质学、土力学、粘土矿物学等理论为指导，采用“现场调查—试验测试—机制探索—模型建立—分析评价”的研究思路，综合运用先进的测试技术、非线性相关分析方法、PFC数值模拟手段，对我国沿海和内陆地区几种典型的不同成因的软粘土，开展结合水特性及其与力学特性的相关性与机理的研究。探索土中结合水与土颗粒的作用机制，提出结合水的类型界定与表征方法；研究结合水对软粘土的基本力学性质、固结蠕变、长期强度的控制作用和机理，建立软粘土结合水与其变形、强度之间的量化关系模型。旨在揭示软粘土变形与强度的本质，从而建立更为精细的软粘土变形与强度的计算模型，丰富土力学的计算理论，为软土性质的改良与软土地基工程设计提供科学的理论依据。

结合水具有复杂的物理化学特性，对粘土物理水理性质、变形与强度特性具有重要影响。结合X射线衍射法（XRD）、X射线荧光光谱分析（XRF）、扫描电子显微镜（SEM）、容量瓶、等温吸附、热失重（TGA）、高压固结、三轴剪切、蠕变试验等技术手段，从宏观和微观两个层面，采取试验测试、理论分析和数值模拟的途径，研究了不同地区软粘土中结合水的特性，提出了软粘土结合水分类和表征方法。采用PFC模拟颗粒与结合水的作用过程，明确结合水对土的力学行为的控制作用及机理。采用非线性相关分析方法，建立软粘土基于结合水特性的变形与强度的量化计算模型。结果表明：软粘土细小孔隙密布，为结合水的分布提供了空间，造成其结合水含量高而自由水含量少。软粘土吸附等温线分为三个不同阶段，其吸附规律分别符合弗雷德里希模型、斯彼朗斯基模型和指数模型。在水气平衡压(p/ps)<0.9的条件下主要是强结合水的形成；在p/ps>0.9条件下吸附水含量明显增大，弱结合水大量形成。结合水在200~250℃的条件下完全脱失。在p/ps<0.98条件下，水合粘土强结合水的初始脱水温度在87~92℃；当温度接近60℃时，弱结合水开始释放，并在90~108℃条件下被完全除去；毛细水和自由水在60℃前脱失。水合粘土的比重随吸附水含量线性下降。水合粘土的体积、吸附水的体积和水膜厚度随吸附水含量均近似线性增加，p/ps<0.9条件下颗粒表面结合水的密度在1.25-1.35g/cm3之间。软粘土的压缩系数随着结合水含量的增大而增大，内摩擦角随结合水含量增加而减小，粘聚力随结合水含量的增加先增加后减小。次固结系数随结合水含量增长而增长。粘滞系数随结合水含量增长总体呈减小趋势。长期强度指标C∞随结合水含量增长呈减小趋势或先增加后减小，φ∞随结合水含量增加而减小。弱结合水在软粘土蠕变过程中起主导因素。强结合水阶段粘土颗粒之间摩擦力最大，随着结合水量的累积，水膜的增厚，颗粒间结合水连接力在逐渐削弱，结合水膜的润滑作用致使颗粒之间的摩擦力也在被减弱。上述研究深入探讨了结合水对粘性土力学行为的影响作用，为精细计算软粘土地基变形及稳定性提供理论依据。