In-situ observation on regularities of rainfall infiltration in loess

One monitoring site was set up in Zhengning county, Gansu province, the changes of soil moisture content within 10.0 m under the condition of natural rainfall were observed continuously in a whole year, and the rules of water migration in loess were analyzed combined with precipitation, evaporation and temperature data. The results show that soil moisture is recharged by rainfall and drains through evaporation in the area. Soil moisture within 1.2 m is affected greatly by rainfall and evaporation, changing in annual cycle, and when the precipitation is more than 18 mm/d, soil moisture content skip suddenly saltatory change, but on the contrary, the circulation of soil moisture occurs mainly in surface layer; soil moisture content almost has no obvious fluctuations on the background trend. The trend is consistent with the change of evaporation. The growth of moisture content increases and the affected depth deepens when the precipitation increases, and the growth decreases and the change of moisture content lags with the depth. Water moves in unsaturated loess in the deep mainly in the form of unsaturated seepage or vapor form, and the motion of vapor is very small, resulting in that soil moisture content grow not only weakly but non-annually, and the water can gather on the surface as encountering layers with low permeability, which is also well reflected by simulated results of the process of rainfall infiltration by finite element software.