Geocomposite Capillary Barrier Drain System with Fiberglass Transport Layer

Abstract

A geocomposite capillary barrier drain (GCBD) removes water from soil while pore pressures remain negative, that is, the soil to be drained does not need to be saturated. GCBDs are being evaluated for inclusion in pavement systems, particularly between the base course and subgrade layer. The GCBD system comprises a capillary barrier layer (a geonet) sandwiched between transport layers (certain geotextiles). Improved GCBD performance is expected with a transport layer that has a greater affinity for water compared with conventional geotextiles. After many materials were evaluated, a woven fiberglass product was selected for further evaluation as a transport layer. A GCBD with a fiberglass transport layer was placed between a subgrade and a base course in a 3-m-long sloped test device used to measure lateral drainage. Water was infiltrated on the top of the base course, and drainage from the GCBD and the soil layers was collected. Measurements of soil suction were made within the soil layers. The GCBD performance was evaluated during three test phases: constant rate infiltration, subsequent drainage with no infiltration, and transient infiltration corresponding to a design storm. The GCBD was successful in draining sufficient water under suction to prevent positive pore water pressures from developing in the base course and to limit water movement into the underlying subgrade soil.

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