van Genuchten模型参数的物理意义

van Genuchten模型是目前拟合水土特征曲线应用最广泛的数学模型，但该模型参数多，且物理意义复杂，特别是参数α的物理意义至今尚未有统一的认识。文章通过理论推导，结合4种样品（粗砂、中砂、细砂和粉砂）实测的水土特征曲线，对van Genuchten模型的参数α、m和n的物理意义进行了探讨，重点研究了α与进气值和拐点处负压（hi）的关系。推导出的van Genuchten模型的1/α与hi的关系和实测数据均证明了1/α不仅与hi有关，还受参数m和n的影响。粗砂和中砂的1/α与hi大致相等，细砂和粉砂的1/α则大于hi。粗砂的进气值与1/α近似相等，其它介质中1/α与进气值之间存在更复杂的关系。另外，m和n作为独立变量在拟合水土特征曲线时精度更高，但在计算非饱和渗透系数时给定m=1-1/n的约束条件是必要的。

Physical significance of the parameters in the van Genuchten model

The van Genuchten model is widely used in fitting soil-water characteristic curves. However, it has numerous parameters with the complex physical significance, and especially the parameter α has not been well understood so far. This paper discusses the physical significance of the parameters α, m and n in the van Genuchten model on the basis of the results of both theoretical derivation and the measured values of the soil-water characteristic curves of the samples (silt sand, fine sand, medium sand, coarse sand), and focuses on the relationships between parameter α and air entry values or matrix potential at the inflection point (hi). The results illustrate that the relationship between the values of 1/α and hi is related to not only hi but also the parameters m and n, and the value of 1/α is approximately equal to hi for the medium sand and coarse sand, while it is greater than hi for the fine sand and silt sand. The air entry value is equal to value of 1/α for the coarse sand, and the complex relationships occur for the other media. In addition, there is a higher degree of accuracy when the water-soil characteristic curves are fitted as m and n are independent variables. It was necessary to give a constraint condition, i.e., m=1-1/n, when the unsaturated hydraulic conductivity is calculated.