Geosynthetic Capillary Barriers in Pavements

"Capillary barrier" is the term for a layer of large-pored material (soil and/orgeosynthetic) placed in a finer-pored soil to 1) reduce unsaturated flow of soil water upwards and/or 2)reduce or prevent water from infiltrating from the overlying fine-pored unsaturated soil into the soilbelow the capillary barrier. In the latter case, the capillary barrier is sloped so that the infiltratingwater flows downwards along the interface between the capillary barrier and the overlying soil. Thesame physical principles govern the behavior of capillary barriers in both cases. This paper reviewscapillary theory and what is known about capillary barriers (made of soil and/or geosynthetics) in avariety of applications. This information is then applied to the potential use of geosynthetic capillarybarriers in pavements to reduce frost heave and to divert infiltrating water. The use of a geocompositecapillary barrier drain (GCBD), consisting of a drainage net sandwiched between geotextiles thatpossess certain hydraulic properties, appears promising. In addition to reducing frost heave, a GCBDmay also help drain the soil above it before it becomes fully saturated. It may also be designed to drainsaturated pavements at critical times of the year, such as spring thaw.