MEASURING WATER TABLE ELEVATIONS WITHIN PAVEMENT SYSTEMS USING TIME DOMAIN REFLECTOMETRY

Measuring changes in the water table elevation below pavement systems is important for understanding pavement performance and improving design applications. Typically ground water monitoring wells are installed at some distance from the actual pavement structure, with measurements usually made manually or with electronic pressure transducers. Time Domain Reflectometry (TDR) methods, using air dielectric coaxial cable to locate the air-water interface in monitoring wells, are currently used in a variety of geotechnical applications. This method for measuring the water table elevation may require less maintenance and be more rugged than using pressure transducers, and provide a means for collecting real-time data from directly below the pavement structure. Laboratory and field experiments comparing TDR, pressure transducer, and manual water table elevations were conducted. An algorithm for locating the air-water interface was developed from laboratory results and applied to field data. Water table elevations measured using the air dielectric coaxial cable compared well to both manual and pressure transducer measurements. The automated system now acquires data, applies the algorithm, and loads the calculated values into a database on a daily basis.

Ruth Roberson, Research Scientist
Minnesota Department of Transportation, Office of Materials and Road Research  
Maplewood, Minnesota

John Siekmeier, P.E.
Minnesota Department of Transportation, Office of Materials and Road Research
Maplewood, Minnesota