Experimental Research on the Land Surface Evaporation of Unsaturated Loess

In order to explore the surface evaporation mechanism of the unsaturated loess,a series of indoor and outdoor evaporating tests were carried out on soil samples with various initial moisture and dry densities. This paper explores the moisture migration rule of the soil samples in the process of the evaporation,analyzes the results of indoor and outdoor experiments and discusses the diversity of those experimenting results. It is concluded that there was a considerable difference in the evaporation intensity and potential evaporation between indoor and outdoor experiments but a small difference in the evaporation coefficient,which was closely related to the water content and was slightly affected by the dry density. The evaporation coefficient of the uniform soil with different initial moisture contents reduced exponentially over time. It further revealed that the soil evaporation coefficient at any time was mainly related to the water content of land surface and the moisture content gradient of the shallow soil. Based on the tested data,a formula which contains the water content of the soil surface and the moisture content gradient of the shallow soil is built up to determine the soil evaporation coefficient.