Experimental study on water seepage law in the tension saturated zone

Purpose In order to look into the water flow law in tension saturated zone (TSZ), which is also called the capillary fringe, one-dimensional seepage experiment in four kinds of porous medium (permeable stone, fine sand, clay, and ceramic plate) was carried out. The permeation flux and apparent permeability of the four kinds of porous media were discussed. The existence of the threshold pressure gradient was also discussed. Materials and methods A special experimental device was designed and the TSZ was formed by artificially controlling the hydraulic conditions. Data were collected and analyzed to show the basic hydraulic characteristics of the four samples. Results and discussion Seepage in the porous media of high permeability (permeable stone and fine sand) under tension saturated conditions kept to Darcy’s law. But in clay and ceramic plate, which are of low permeability, the relation between permeation flux and hydraulic gradient was controlled by hydraulic gradient, and when hydraulic gradient increased to a specific value, water flow obeyed Darcy’s law and apparent hydraulic conductivity was a constant value equal to that under saturation. The existence of the threshold pressure gradient was not proven when flow occurred in clay and ceramic plate which are of low permeability. Conclusions Water flow law in the TSZ was discussed by conducting indoor experiments through which we took a brief look at the seepage characteristics in different porous media in the unique region of the vadose zone and verified the common percept of unsaturated flow.