Modeling pavement subdrainage systems

A comprehensive study of pavement subdrainage systems was conducted. In the study, three test sections were constructed as part of a new bypass, I-469, at Fort Wayne, Indiana. Location of the drainage layer and materials for the bituminous base course and filter materials were varied from section to section. Instrumentation was installed in the three sections during construction and included sensors to measure temperature, frost, and moisture. Tipping bucket flowmeters were attached to the subdrainage system outlet pipes. A rain gauge was located at each section. A comprehensive laboratory testing program was conducted in the study. Hydraulic conductivity tests were conducted on subgrade, filter, pavement, and trench materials. In addition to conventional saturated permeability, moisture-suction tests were conducted on all materials to determine their partially saturated permeability. Movement of water through the three pavement sections was modeled by using the finite element method analysis. Laboratory-determined hydraulic properties of each material were input directly to the analysis. Several rainfall events were analyzed. Two events were used to verify the analysis model. Subsequent analyses were conducted on new events. Data were recorded for the three sections for 3 years. Measurements indicated that one of the three subdrainage sections drained in one-third the time of the other two sections. This was in agreement with the finite element method analysis. Also, a theoretical subdrainage section was analyzed by using optimal materials from all three sections. This optimized section was shown to further reduce the time of drainage. Conclusions and recommendations address drainage layer location, filter materials, material permeability, and collector pipe capacity.