This project developed and evaluated the effectiveness of a geocomposite capillary barrier drain (GCBD) system (Figure 1) in preventing pavement damage by controlling moisture movement in pavement subgrade and base course. A number of geotextiles were evaluated for their suitability as a transport layer using a series of tests that included capillary rise, moisture retention, function measurements, siphoning and transmissivity under suction. At infiltration rates that occur in the field, the GBCD drained water from overlying base material that was not saturated. Furthermore, the GBCD prevented the moistening of the subgrade at many of the filtration rates tested. This allows the design of unsaturated soil drainage to help extend pavement life by limiting the time the bases are saturated and by diverting large volumes of water to a drainage system before it reaches the subgrade. In the specific GBCD tested, water drained from overlying base soil when subjected to suction head of 100 mm and greater. Furthermore, at long term infiltration rates of 0.1 to 0.15 mm/hr, the GBCD prevented infiltrating water from reaching the subgrade. Finally, the GBCD recovered its function and protected the subgrade in a test following a test in which a small amount of water had broken through the GBCD into the subgrade. Further development is needed before the technology can be implemented and a more economical transport layer than the one tested in this project would make GBCD more affordable and implementable. The contractor is discussing the possibility of licensing the technology with a private manufacturer of geotextiles. The project was highlighted in a recent issue of Progressive Engineer, an on-line engineering magazine and information source.  

The final report for this IDEA project can be found at:
https://www.trb.org/studies/idea/finalreports/highway/NCHRP068_Final_Report.pdf