Extending TDR capability for measuring soil density and water content to field condition monitoring

Time domain reflectometry (TDR) can be used to measure the dry density of compacted soils, although it is believed that TDR could also be used to monitor the long-term performance of aging geotechnical assets. Understanding the deterioration of aging assets (earth dams, embankments) can be problematic; monitoring the relative condition with time may prove advantageous. In such applications, it would be likely that commercially available TDR probes and multiplexers would be used, and this paper illustrates that the current method does not perform particularly well with these. Therefore, an alternative method has been developed that, when applied to six fine-grained soils (exhibiting a range of plasticities), can deal with the impacts of multiplexers and commercial probes. It is shown that the dry density and gravimetric water content can be predicted with an accuracy of ±5 and ±2%, respectively. The accuracy can also be improved by correcting the TDR parameters for temperature. The new method is robust, relatively independent of the compactive effort and only marginally affected by the presence of multiplexers, making it suitable for field-monitoring applications.