Effect of Soil-Particle Size Contrast on Capillary Barrier Performance

Abstract

Capillary barriers, consisting of sloping layers of fine over coarse soils, have been investigated as an alternative for hydraulic isolation of buried waste. Based on analytical results, it is known that the lateral diversion of water over a capillary barrier interface is maximized as the soil-particle size contrast becomes infinitely large. However, practical limitations affecting interface integrity and slope stability restrict the reasonable particle-size contrast. In this note, design guidance is provided for selection of soil-particle size contrast in a capillary barrier system. Results indicate that near-maximum lateral diversion of water can be obtained with a modest contrast between the fine and coarse materials of a capillary barrier. For a given combination of infiltration rate, interface slope, and fine material characteristics representing the most conservative case, 80% of the maximum diversion can be obtained with an underlying coarse material that is only 2.5 times coarser than the overlying fine material. With a coarse material that is 5 times coarser than the overlying fine material, 90% of the maximum diversion is obtained.