Model tests on capillary-barrier cover with unsaturated drainage layer

Model tests are carried out to study the response of capillary-barrier cover with unsaturated drainage layer under heavy rainfall situation. The test equipment includes a model box with a dimension of 2 m×1 m×1.2 m, a rainfall simulator and measuring facilities. The materials of fine layer, unsaturated drainage layer and coarse layer of the capillary-barrier cover model are silt, sand and gravel respectively, and the gradient of model is 1<>V: 3<>H. The intensity of simulated rainfall is 65~76 mm/h. During the tests the rainfall infiltration process and lateral drainage phenomenon are observed, and the surface runoff, lateral drainage and percolation through capillary-barrier cover are measured. In Test Ⅰ, runoff accounts for 69.4% of the total rainfall, and most of the infiltration is stored in the silt layer. The lateral drainage of the sand layer is significant, being 3.5% of the total rainfall; and the percolation through the cover is 2.9% of the total rainfall. In Tests Ⅱ and Ⅲ, the infiltration flux is reduced by an addition of bentonite into the silt layer. A delayed response in the lateral drainage is observed in the sand layer, and the percolation is reduced to only 0.8% of the total rainfall in Test Ⅱand no percolation is observed in Test Ⅲ. The model test results indicate that the percolation through the capillary-barrier cover can be controlled under heavy rainfall condition by reducing rainfall infiltration and enhancing capillary barrier effect and lateral drainage capacity. The research makes the application of capillary-barrier cover in humid regions feasible.