基于孔隙连通–迂曲参数表征土的非饱和渗透各向异性

Represention of anisotropy in unsaturated permeabilities for soils based on pore connectivity-tortuosity parameter

合理描述土的非饱和渗透各向异性对模拟土体内水分和污染物的迁移至关重要。基于Mualem提出的非饱和渗透系数函数引入的孔隙连通–迂曲参数,推得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,并根据该表达式将土的非饱和渗透各向异性划分为9种类型,发现各向异性系数随有效饱和度的变化过程中会出现土孔隙内水分主导流动方向变化的门槛点;再利用已有文献中基于孔隙网络模型模拟土样的非饱和渗透数值试验结果验证了该表达式的有效性;最后,将该表达式与Van Genuchten-Mualem函数相结合,定量描述了基质吸力对已有文献中4种土的非饱和渗透各向异性影响。

Accurate characterization of the anisotropy in unsaturated permeability for soils is significant in simulating flow and contaminant transport. Based on the Mualem’s unsaturated permeability function, the power type expression for the relationship between the anisotropy coefficient and the effective degree of saturation is derived by introducing the pore connectivity-tortuosity parameter so as to describe the nine types of the anisotropy in unsaturated permeability. In the process of anisotropy coefficients varying with the effective degree of saturation, there exists a critical point at which the dominance of flow direction switches. This expression is then validated using the numerical test results of unsaturated permeability of a pore network for modeling the soil samples in the previous literatures. Combining with the Van Genuchten-Mualem function, this expression can be finally used to represent the effect of matric suction on the anisotropy in permeability for four soils in the existing literatures.