Geosynthetic Capillary Barriers in Pavements

"Capillary barrier" is the term for a layer of large-pored material (soil and/or geosynthetic) 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 soil below the capillary barrier. In the latter case, the capillary barrier is sloped so that the infiltrating water flows downwards along the interface between the capillary barrier and the overlying soil. The same physical principles govern the behavior of capillary barriers in both cases. This paper reviews capillary theory and what is known about capillary barriers (made of soil and/or geosynthetics) in a variety of applications. This information is then applied to the potential use of geosynthetic capillary barriers in pavements to reduce frost heave and to divert infiltrating water. The use of a geocomposite capillary barrier drain (GCBD), consisting of a drainage net sandwiched between geotextiles that possess certain hydraulic properties, appears promising. In addition to reducing frost heave, a GCBD may also help drain the soil above it before it becomes fully saturated. It may also be designed to drain saturated pavements at critical times of the year, such as spring thaw. I N T R O D U C T I O N "Capillary barrier" is the term for a layer of large-pored material (soil and/or geosynthetic) 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 finepored unsaturated soil into the soil below the capillary barrier. In the latter case, the capillary barrier is sloped so that the infiltrating water flows downwards along the interface with the capillary barrier (e.g., Ross, 1990) (Fig.l). Because both cases involve unsaturated flow, the same physical principles govern the capillary barrier behavior. We are interested in the use of geosynthetic capillary barriers in pavements to perform both functions: to reduce frost heave by preventing upward water flow 1U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, NH. 2Department of Civil Engineering, University of New Mexico, Albuquerque, NM. 3Department of Civil Engineering, University Washington, Seattle, WA.