考虑气-液交界面的非饱和土有效应力公式

An effective stress formulation for unsaturated soils considering air-liquid interface

在本构关系中如何确定有效应力是非饱和土力学界的重要课题之一。将非饱和土简化为气、液、固三相及其交界面组成的集合体。基于热力学原理,在Helmholtz自由能中考虑力-水耦合特性,将各相及其交界面的质量、动量、能量、熵守恒方程及相应的限制条件与自由能函数的物质导数联立代入熵不等式,根据该不等式适用所有热力学状态的条件推导出考虑气-液交界面面积密度的有效应力公式,并在利用该公式确定有效应力参数时将气-液交界面的面积密度表示为基质吸力与饱和度的函数。最后,利用已有文献中3种土的多阶段减、增湿三轴剪切试验结果,验证了该有效应力参数表达式相较于已有文献表达式在描述干湿循环下有效应力参数与基质吸力关系时的优势。

How to determine effective stress has received much attention in the constitutive relationship of an unsaturated soil, which can be simplified as an assembly consisting of air, liquid, solid phases and interfaces in contact with each phase. Based on thermodynamic principle, application of conservation equations of mass, momentum, energy, entropy for phases and interfaces, corresponding constraint conditions along with the entropy inequality, combined with Helmholtz free energies accounting for hydro-mechanical coupling, a new effective stress formulation is developed to take into account the contribution of the areal density of air-liquid interface. Moreover, a function for areal density of matric suction and degree of saturation is used to determine effective stress parameter in the resulting formulation. This parameter expression is finally verified using the multistage drying-wetting triaxial shear test data for three soils in the exisiting literatures. The results show that this expression is superior to other one in previous work for describing the relationship between effective stress parameter and matric suction under cyclic drying-wetting.