Improving TDR for use with fine-grained soils

Time-Domain Reflectometry (TDR) provides a robust and widely used method for the monitoring and characterisation of soils using user-friendly cable testers. However, the simplicity of common TDR practice, often utilizing only measurements of reflection distances for electromagnetic signals in probes, causes a number of difficulties when applied to fine-grained soils, largely because they can be electromagnetically dispersive: that is their dielectric 'constants' vary with frequency. This paper therefore considers two ways in which TDR data can be made to greater use in geotechnical disciplines: supplementing TDR with frequency-domain data, and addressing the issues of standardisation and data sharing.