Evaluating Roadway Subsurface Drainage Practices

Project summary:

The project involved the evaluation of the efficacy of drainage systems for drainage of roadway base materials via three separate sets of experiments. In the first set, two drainage treatments were examined, one in drains located on the roadway edge, and the other in drains installed along the roadway centerline. For the purposes of this project, the measure of efficacy was the degree to which the roadway base and sub-base material was drained. In the second set, drains were examined to determine whether the elevation of the roadway relative to the surrounding landscape has a significant impact on the efficacy of the drain. In the third set, drains were examined to determine whether the amount of crushed concrete aggregate present in the roadway base has a significant effect on drain performance; researchers were concerned with plugging of drains by soluble calcium coming from the concrete aggregate. In all experiments, drains flows were monitored with tipping bucket units to measure cumulative drain outflows. A non-invasive moisture measurement method based on electromagnetic induction were tested for measuring moisture in roadway base and sub-grade materials, and this method was used to acquire data on moisture content in the roadways associated with the different drainage treatments. This moisture content information was used to assess the performance of drains, and was related to the amount of drain outflow. Researchers used statistical analysis of acquired data to evaluate the efficacy of the various drainage treatments, then derived guidelines for drain system design standards. A numerical model of water flow in roadway base and sub-grade materials was tested using moisture data collected at a field site where drains are present. The model was used to evaluate various drain configurations to provide some guidance to roadway engineers about where to place drains in specific situations.