基于“土样—土颗粒—集合体”多层次分析的非饱和土水力特性研究

On the basis of particle mechanics, interface science, and hydrodynamics, a novel multi-level analysis of “soil specimen-soil particle-assembly” is proposed to study the hydraulic behavior of unsaturated soils. Firstly, the water retention curves for soil specimens are simulated by existing models. The traditional water retention model at relatively high moisture is extended to the cases at lower moisture. Then a new permeability model for unsaturated soils is proposed by taking into account the capillary and film flow. Secondly, a soil specimen can be simply divided into several uneven-sized sphere particles, where water form can be characterized by liquid bridge. A theorical model is developed to study the evolution of capillarity force for the liquid bridge between uneven-sized wet particles with ratio of particle radius, particle separation and liquid volumes. Finally, an unsaturated soil is simplified as a nonuniform soil particulate assembly consisting of uneven-sized sphere particles, relatively loose and relatively dense packing assemblies are then generated based on the measured grain size distribution of soil. After analyzing the water retention and flow law in unit pores formed among particle assemblies, physical models are put forward for water retention and permeability of nonuniform soil particulate assembly. A series of questions about the action mechanism of matric suction on “soil specimen-soil particle-assembly” will be resolved theoretically, the friuts of the project will then deepen and perfect the explanations of inner hydraulic mechanism, which can provide a novel approach to study water retention and permeability behavior for unsaturated soils.

以颗粒力学、表面科学及水动力学为基础，采用“土样—土颗粒—集合体”的多层次分析模式，从理论上研究非饱和土的水力特性。首先，从土样试验结果的模型描述出发，将适用于高湿度范围的传统持水模型推广至低湿度范围，并在全湿度范围内建立综合考虑毛细和薄膜流动的非饱和渗透模型；其次，将土样简化分散为不等径球体颗粒，用液桥表征颗粒间的水分形态，研究液桥从形成至断裂时毛细作用力与颗粒半径比、颗粒间距、液桥体积的理论关系；最后，将非饱和土简化为不等径球体颗粒组成的不均匀土颗粒集合体，利用土的颗粒级配试验结果生成较松散和较密实排列的2种颗粒集合体，研究其单元孔隙内水分的含量及流动规律，建立表征其持水与渗透特性的物理模型。研究成果将从理论上回答基质吸力对“土样—土颗粒—集合体”持水与流动特性作用机制的一系列问题，深化和完善对非饱和土水力特性的内在机理认识，为非饱和土持水与流动特性的研究探索出一条新途径。

水力-力学特性是当今非饱和土力学研究的热点和难点之一。基于表面科学、颗粒力学、水动力学与热力学原理，提出了“土样-土颗粒-集合体”的细-宏观多尺度分析模式。先从土样的试验结果出发，实现了土在全含水率范围内持水及非饱和渗透特性的模型描述，并利用持水曲线提出了预测非饱和土相对渗气系数的新方法，基于孔隙连通-迂曲参数推得了非饱和渗透各向异性系数关于有效饱和度的幂函数表达式；再将土颗粒中的粗粒和细粒分别简化为不等径球体颗粒和平行片状颗粒，用液桥表征颗粒间的水分形态，提出了考虑固-液接触角影响的粗粒间液桥毛细力计算方法，并分析了细粒间液桥从形成至断裂时毛细力的演化规律；对土颗粒级配曲线上划分的粒组分别构建形如立方体的天然土颗粒以及理想球体颗粒集合体，对比分析这两者的几何特征和物理性质，并依据理想圆柱形孔隙与天然土孔隙内水分流量的相似性，提出了预测持水曲线与非饱和渗透系数函数的物理方法；最后，将非饱和土简化为各相及其交界面组成的集合体，在Helmholtz自由能中考虑力-水耦合特性，推导出考虑气-液交界面面积密度的有效应力公式。研究成果深化和完善了对非饱和土水力-力学特性的内在机理认识，为非饱和土持水-流动特性与有效应力研究探索出一条新途径。