Summary Of New Developments In Tdr For Soils

Abstract

Time Domain Reflectometry (TDR) is a method to determine the electromagnetic properties of soils and recent research indicates that TDR is an increasingly powerful tool to assess the engineering properties of soils. There were symposia and workshops on this topic held in 1994 and 2001 at Northwestern University and one in September 2006 at Purdue University. The authors were among the organizers of TDR 2006: 3rd International Symposium and Workshop on Time Domain Reflectometry for Innovative Soils Applications (TDR 2006) at Purdue University on September 17-20, 2006. There were five keynote presentations and thirty-five paper presentations with much discussion among the more than 70 researchers and practitioners from agricultural engineering, agronomy, electrical engineering, geotechnical engineering, soil science, and soil physics. The five themes were: 1) TDR Calibration in Challenging Media, 2) Geotechnical Applications of TDR, 3) Innovations, Challenges, and Future Opportunities, 4) TDR Probe Design and Selection, and 5) Hydrologic Applications of TDR. Papers to TDR 2006 are available free of charge on line at https://engineering.purdue.edu/TDR. This paper presents highlights of some interesting papers to TDR 2006. Items to be discussed include: effects of geometrical and interfacial factors on effective permittivity, improved methods for volumetric water contents for pavement bases and subgrades, cone penetrometers to measure permittivity and conductivity, a new TDR source signal that is non dispersive, and soil texture characterization from TDR waveforms. Unfortunately only a few of the many excellent papers could be highlighted. The paper concludes with a quotation from the presentation of G. Clarke Topp, the acknowledged father of modern TDR for soil moisture measurement.