Research Of Layered Unsaturated Sand Media Infiltration Test Under Non-ponding Water Condition

Soil is a sort of complicated porous media. soil water, a link of meteoric water andgroundwater, is an important part of the hydrologic cycle. After rainfall and irrigationinfiltration into soil water, it can be absorbed and utilized by plants. In addition, oneof the renewable recharge sources of groundwater is the infiltration of soil water.Unsaturated zone soil is the only entry of various pollutants from surface intogroundwater, in the case of groundwater pollution, environmental pollution isgenerally generated in the earth’s surface and only through the unsaturated zone, can itbe enter into groundwater. The lithology in unsaturated zone is one of theconsiderable factors influencing the water infiltration. Due to the effect ofmeteorology, hydrology, geology and biology etc, the structure of natural soil is oftenlayered. As a result, The research of layered media of water and solute transport inunsaturated zone has become prevalent and leading in hydrogeology field nowadays.At present, there is little study involved in layered sand media under the conditionof non-ponding infiltration. With the support of the key research project, named theexperimental research on solute migration in unsaturated zone, in State KeyLaboratory of Geohazard Prevention and GeoenvironmentProtection(SKLGP2011Z001), this paper has designed three kinds of water infiltrationtests with different content of layered sandy soil under the non-ponding condition,analyzed water content and matrix suctions over time in the test process andestablished the water migration model of layered sand media under the condition ofthe non-ponding infiltration in unsaturated zone.The concrete research results are as follows:1. Under the condition of the non-ponding infiltration, the water content of layeredunsaturated sand media is changed periodically. In the first stage of water infiltration, the growth of the water content is linearly changed, and to a certain stage there issecond linear growth in each layer of medium on the bottom profile. After the lineargrowth, the higher content of medium section is gently changed, then reaches thestable water content, while lower content of the medium section reaches the stablewater content immediately at the end of the linear growth.2. Under the non-ponding infiltration condition, in the same layer media, thelinear growth rate of water content bears an inverse relation to the depth of the profilefor a linear change. For the two linear phases change profile of water content, the firstlinear change rate is larger than the only ones, approximately ten times.3. Under the non-ponding infiltration condition, The linear growth peak is almostthe same of water content for the same layers in different depth of profile.The lineargrowth peak is inversely proportional to silt content for different sand content of themedia.4. Still, it is identical of stable water content in different depth profile and it is aninverse relationship between stable water content and silt content under different sandcontent media.5. Under the non-ponding infiltration condition, the matrix suctions change can beroughly divided into three stages about the media: firstly, the matrix suctions remainoriginal values for the late water migration to the corresponding section in this phase;secondly, it is rapidly changed, water migration to the corresponding section in thisphase, for the rapid increase of the water content results in the fast change of thematrix suctions; thirdly, the matrix suctions come to a balance value at end of rapidchange, and remain unchanged. Among above, Logistic functions is available forfitting change trends of the second and third phases when the matrix suctions begin tochange.6. At the same conditions as above, the initial matrix suctions of different profilesis increased with the growth of the depth profile in the same layer media and thestable matrix suctions are almost alike in each profile. In terms of different sandcontent media, the initial matrix suctions is inversely related to sand content and thestable matrix suctions are approximately equal in each profile.