Performance Evaluation of Roadway Subdrain Outlets in Iowa

Abstract

The bearing capacity and service life of a pavement are adversely affected by the presence of undrained water in the pavement layers. In cold winter climates, such as in Iowa, this problem is magnified further by the risk of frost damage when water is present. Therefore, well-performing subsurface drainage systems form an important aspect of pavement design by the Iowa Department of Transportation (DOT). However, there was a need to determine the impacts of not maintaining the subdrain outlets on pavement performance in Iowa in light of the recent Iowa DOT field maintenance staff reductions and budget cuts and the implications on subdrain outlet maintenance. Consequently, a research study was initiated to conduct a performance review of primary interstate pavement subdrains in Iowa and determine the cause of the problem if there were drains that were not functioning properly. Field investigations were conducted on 64 selected (jointed plain concrete pavement and hot-mix asphalt) pavement sites during the 2012 fall season. The study was mainly focused on the drainage outlet conditions. Findings and observations based on an extensive literature review and forensic testing are discussed in this paper. Gate and mesh screen-type rodent guards are not recommended for Iowa subdrainage systems because they tend to catalyze outlet blockage and end up potentially doing more harm (i.e., requiring more frequent maintenance) than good (i.e., protection against rodent intrusion).