Draining unsaturated soils with geosynthetics

ABSTRACT: The geocomposite capillary barrier drain (GCBD) comprises three layers that are, from top to bottom: a transport layer (a specially designed geotextile), a capillary barrier (a geonet), and a separator (geotextile). The GCBD was developed as a means to remove water from unsaturated soils. The transport layer removes water under negative pressures, the capillary barrier stops upward and downward unsaturated flow of water from adjacent layers, and the separator prevents underlying soil from intruding into the capillary barrier. This paper summarizes investigations and proof-of-concept studies related to the development of the GCBD, including laboratory and field studies. Capillary rise, moisture characteristic curves, and unsaturated transmissivity measurements were used to select candidate transport layers for evaluation in GCBD systems. Large-scale laboratory tests of pavement sections indicate that, when placed between a pavement base and subgrade, the GCBD will: (1) accelerate the draining and drying of the base; and (2) reduce subgrade wetting. Subsequent field studies validate these conclusions, and confirm that pavement sections with a GCBD system have lower water contents.