Performance of Permeable Bases

Critical aspects related to the design, construction, maintenance, and performance of permeable bases are examined, and a case study is presented to put such considerations in a more practical perspective. While the popularity of carefully designed subsurface drainage systems is justified by sound engineering considerations, and their performance has been generally satisfactory, their general use is not free of problems. Disappointing local experiences sometimes discourage agencies from specifying permeable bases. One such example is offered by the United States Route 50 test road near Athens, Ohio, for which the performance of the permeable base in the context of the overall subsurface drainage system is investigated. It is found that almost one-third of the outlets at the site could not be located, and that due to little or no maintenance many of the remainder had been silted in. Software DRIP 2.0 calculations affirm that outlet spacing is adequate, yet a considerably higher permeable base thickness is required, and that the permeability of one of the gradations used is too low. Moreover, the absence of a compatible separator layer between the permeable base and subgrade exposes the system to the danger of clogging.