Experimental study of 1-D capillary barrier model using geosynthetic material as the coarse-grained layer

In general, a capillary barrier system is constructed using a fine-grained soil overlying a coarse-grained soil. Experimental results of two 1-D capillary barrier models are presented in this paper. The first capillary barrier model was constructed using gravelly sand as the coarse-grained layer and the second capillary barrier model was constructed using geosynthetic material as the coarse-grained layer. The geosynthetic material used in this study is Polyfelt Megadrain 2040, which consists of a matrix of polypropylene monofilaments sandwiched between two layers of polypropylene geotextile. Fine sand was used as the overlying fine-grained layer for both capillary barrier models. Below the gravelly sand and the geosynthetic material, fine sand layers were placed to represent the original soil which is protected by the capillary barrier model. Several infiltration tests followed by drying processes were applied to the capillary barrier models. Measurements of pore-water pressures (PWP) and volumetric water contents along the capillary barrier models were used to study the behavior of the models. The test results showed that both gravelly sand and geosynthetic material were able to create capillary break. Both capillary barrier models were able to maintain the PWP above and below the coarse-grained layers at negative values. The geosynthetic material was found to be more effective than the gravelly sand to be used as the coarse-grained layer in a capillary barrier system due to the fact that the PWP head above the geosynthetic material was lower than that above the gravelly sand layer. Therefore, the unsaturated permeability of the fine-grained layer above the geosynthetic material was lower than that above the gravelly sand layer. As a result, water did not infiltrate easily into the soil layer above the geosynthetic material. Copyright ASCE 2006.