The forest service conducted an in-depth laboratory and field investigation to evaluate geocomposite drain systems for use on low-volume roads. The laboratory testing program was designed to determinethe flow capacity of various manufactured systems when subjected tovarying lateral loads and hydraulic gradients. Because no standard tests were available to evaluate geocomposite drain system performance under field conditions, a test system consisting of a large triaxial chamber and special plumbing was developed. Geocomposite test specimens were placed vertically in a 6- by 12-in. Mold, which was then filled with a compacted silty soil. Changes in flow rates through the specimens were measured as both the gradient and lateral pressure were varied. A wide range in performance was noted among the different systems. At the lower confining pressures, the flow capacities were fairly similar. As the confining pressures were increased, the flow capacity of some drain systems dropped markedly. However, all products tested, except one, had a minimum flow rate of about 1 gal/min per foot of drain width when subjected to a confining pressure of 30 psi and a hydraulic gradient of 1.0. In conjunction with the laboratory testing, three field installations of prefabricated drain systems were instrumented. All three sites had piezometers in front ofand behind the drain systems, and one site had an outflow recordingdevice. Results of these installations validated the laboratory test results. This paper appears in transportation research record no. 1291, Fifth international conference on low-volume roads, may 19-23, 1991, raleigh, north carolina, volume 2.
Abstract