Calibration Procedure for a Time Domain Relectometry (TDR) Apparatus to Measure Volumetric Water Content in Pyroclastic Soils

Abstract

This technical report describes an experimental procedure to calibrate a Time Domain Reflectometry (TDR) system to measure volumetric water content in pyroclastic soils. The TDR technique is based on the measure of dielectric constant of a soil to estimate its volumetric water content. Even thought the well known experimental tests performed by Topp et al. (1980) evidenced as the variation of dielectric constant in a soil is closely connected to the change of its water content, other authors (Regalado et al. 2001, Regalado et al. 2003, Roth et al. 1992, Tomer et al. 1999, Weitz et al. 1997) have showed that for a volcanic soil other factors as porosity, bulk density and surface area can affect the variation of soil dielectric constant. For this reason the authors suggest to perform always an appropriate calibration phase before use TDR. As the TDR technique will be employed in the experimental test performed with lisimeter to investigate the water retention curve of pyroclastic soils, the calibration of TDR apparatus is necessary to estimate the correct relationship between the variation of water content and the related change of the idro-mechanical behaviour of the soil.