Experimental Research On Infiltration In Unsaturated Loess

The field investigation found that underground water level is generally higher than river water level in loess area. This makes the groundwater lose near river water supplies. So the atmospheric precipitation(local irrigation) becomes only recharge source of groundwater in the region. By observing the moisture content of different depth profiles, it is found that the infiltration depth of surface water in the loess is limited and difficult to reach the underground water level. This paper revealed the rule of rainfall infiltration and the mechanism of groundwater recharge in the unsaturated loess by experiment.Because of previous study with short duration and depth can`t to explain whether the groundwater table are affected by precipitation or Irrigation. Setting up monitoring stations in zhengning county, gansu province, this paper excavate a deep 96.0m, 1.0m diameter observation wells used to monitor the full process of the surface water infiltration and groundwater recharge in the loess tableland area. The ground rain gauge, pressure gauge, air thermometer and hygrometer were set in the ground surface to obtain the related monitoring data. Soil moisture meter were inserted on the Wall of wellto monitor the change of soil moisture content in the process of water infiltration. Water level gauge was set under the water surface to monitor water level. The result shows soil moisture content increases caused by rainfall, maximum influence depth less than or equal to 4.0 m; The greater the rainfall, the soil moisture content increases more, the greater the moisture content increases the faster response time, the greater the influence depth, with the increase of depth, increase decreases, and gradually with time lag; Unsaturated loess, the water infiltration is mainly in the form of unsaturated seepage flow or water vapor migration; the influence of underground water level by pressure and Celestial bodies, there is an obvious well tidal phenomenon.The result of monitoring showed the moisture would change within 0.4m of loess, thus soil column experiment was conducted with this depth. Malan loess(L1) side with the Loess Plateau was loaded in the organic glass cylinder then watered every day. The moisture and matric suction were recorded regularly during this process. It is found that the moisture above wetting front was nearly invariable, the ratio of maximum of moisture to saturated moisture was 0.7445. Based on three theory models of Gardner, vanGenuchten and Fredlund&Xing, the soil-water characteristic curve of remolded Malan loess were obtained by fitting test data included moisture and matric suction. The result showed the curve used by Fredlund & Xing model is best.At the same time, using the Geo- Studio model monitoring wells and soil column experiment were established to simulate rainfall infiltration process in the loess. In the two simulations, rainfall infiltration in loess were to unsaturated form of transport, the simulation results fits well with the field monitoring results and the soil column test results. Water seepage in the loess belongs unsaturated seepage, it provides a basis for the application of the theory of unsaturated theory in practical engineering.