The objectives of this research were i) to evaluate the performance of pavement subdrainage systems ii) study the behavior of moisture conditions below pavements and iii) provide recommendations for unproved drainage criteria based on analysis of field data. Existing and retrofitted subdrainage collector systems were inspected through external visual inspection in combination with a probe for internal inspection. Distresses and deficiencies in construction observed were listed and compiled on video. A methodology for inspection is presented that can be used by highway agencies in monitoring the condition, need for maintenance, and performance of collector systems. Pavements with various types of subdrainage systems were instrumented to monitor the effects of different parameters influencing flow. The instrumentation package included pressure transducers, moisture blocks, thermistor probe, rain gauge, tipping bucket flow meter and a data recording and storage system. Laboratory investigations were conducted on subgrade and subbase samples collected from instrumented sites to assess their material and hydraulic properties. Parameters obtained by fitting Brooks & Corey's model and Van Genuchten's model to experimental data have shown good correlations with measured values. Data collected from instrumented sites show varying response rate and time of outflow with respect to precipitation for different types of pavements and collector systems. Statistical Analysis has shown significant influence of base permeability in addition to pavement and drain types on pavement outflow. High correlations exist between precipitation and pore pressure underneath pavements. Data from instrumentation and laboratory tests will help in calibrating and validating an analytical seepage program developed separately as part of this research project.

Report Number



pavement subdrainage, collector systems, inspection, instrumentation permeability, precipitation, outflow, seepage program, HPR-2018

SPR Number


Project Number


File Number


Performing Organization

Joint Highway Research Project

Publisher Place

West Lafayette, IN

Date of this Version