Drainage system performance after 20 years

As part of a study of the longevity and effectiveness of clay, bituminous fiber, and concrete drainage pipes, several pairs of these pipes were installed in a heavy clay soil at the Imperial Valley Agricultural Center at El Centro, California in January 1964. Drain lines were laid at a depth of 7 feet and a spacing of 120 feet. Bituminous-fiber drains were installed in a fiberglass envelope; washed gravel was used to enclose the clay and concrete pipes.