Study On The Water Migration In Aeration Zone Of Loess Slope On ZhaiTou Village

This paper is supported by the major disaster mechanism of loess and hazard chain evolution research, the National Basic Research Program of China(973 Program). There are three test in this paper: outdoor infiltration test, indoor permeability test and soil moisture characteristic curve test(the PF curve test). With these tests, it can get parameters about loess. According to unsaturated percolation theory, the movement of water in the aeration zone of loess can be simulated with the software, and the law of water movement in aeration zone can be researched under the effects of different the external factors.The test site is located on the loess slope of ZhaiTou village in Shaanxi province. And according to the observed data, the law of moisture migration can be analyzed in aerated zone. At the same time, exploratory trench is excavated on the loess slop, and the depth is 1m. With ring sampler, soil samples are got in situ. The saturated hydraulic conductivity of loess can be got from the permeability test about these samples. Furthermore, it can get soil moisture characteristic curve from the PF curve test. On the basis of the curve and the saturated-unsaturated percolation theory, it can get the relationship between the saturated and unsaturated hydraulic conductivity. Thus model parameters are provided for the numerical simulation.Based on the unsaturated percolation theory, the aerated zone of loess slope in the ZhaiTou village is conceptualized and the vertical cylindrical two-dimensional unsaturated and unsteady-state flow model is built. With the help of model, it is completely simulated that the movement of water in the aeration zone. Besides, the model is corrected with infiltration test, and in the light of the results, it is right to obtain the distribution characteristics of moisture migration in aerated zone. In addition, soil moisture has changed in the superficial aeration zone of loess, and the scope of the change in the vertical direction is greater than the scope in the horizontal direction, the depth is less than 4m.Moisture migration of vadose zone is influenced by three factors: precipitation, evaporation and the gradient of the loess slope. The precipitation is divided into three: continuous rain(time is 24 h, precipitation intensity is 3 mm/h), short-time storm(time is 2h, precipitation intensity is 36 mm/h) and no rainfall. The evaporation is divided into two: strong evaporation(evaporation intensity is 0.5 mm/h) and weak evaporation(evaporation intensity is 0.05 mm/h). The gradient of the loess slope is divided into three: 1:1,1:0.67 and 1:0.33. Three kinds of factors work together and there are a total of 18 kinds of research programs in this paper. According to the unsaturated percolation theory, the moisture migration of vadose zone of the loess slope is vertical two-dimensional unsteady unsaturated flow, and with the software, numerical model is set up. The results of model with the 18 programs are compared and analyzed, and the law of moisture migration of the loess slope in the vadose zone can be acquired. The main conclusions were as follows:1. It is found that the depth of moisture migration of the loess slope in the vadose zone is 4m in the infiltration test.2. Soil moisture content in the vadose zone of the loess slope is largely unchanged, but there is still a moisture migration.3. Compared with short-time storm(time is 2h, precipitation intensity is 36 mm/h), the water infiltrates easier under continuous rain(time is 24 h, precipitation intensity is 3 mm/h).4. It is able to obtain that strong evaporation has a mightily effect on moisture migration.5. The free face of slope loess slope is gently, and it will be beneficial to precipitation recharge and evaporation excretion. In contrast, the free face is steep, it will be against to precipitation recharge and evaporation excretion.