On the relationship between matric potential and dielectric properties of organic free soils: a sensitivity study Norman Wagner and Alexander Scheuermann Abstract: High-frequency electromagnetic determination of moisture in porous media, (e.g., soil) is based on the strong re- lationship between volumetric water content and relative dielectric permittivity. In particular, in fine-grained soils the movement of water is influenced by different surface-bonding forces due to interface processes. The interface effects lead to a number of dielectric relaxation processes (free- and bound-water phase, Maxwell–Wagner effect, counterion relaxation effects). These relaxation processes are the reason for the strong frequency dependence of the electromagnetic material properties below 1 GHz. The matric potential is a measure of the bonding forces on water in the soil. Based on a thermo- dynamic relationship between soil matric potential and dielectric relaxation behaviour of water in different binding states, a broadband dielectric relaxation model was developed that considers low-frequency dispersion up to 1 MHz as well as losses due to direct-current conductivity. The sensitivity of the model on soil suction was systematically analyzed based on a pedotransfer function (PTF) for soil textures ranging from pure sand up to pure clay. The results are compared with known empirical and semiempirical calibration functions, as well as theoretical mixing models. Key words: soil matric potential, dielectric spectroscopy, time-domain reflectometry (TDR), soil moisture. Re ´sume ´: La de ´termination de l’humidite ´ dans un me ´dium poreux (par exemple le sol) avec des hautes fre ´quences e ´lectro- magne ´tiques est base ´e sur la forte relation entre la teneur en eau volumique et la permittivite ´ die ´lectrique relative. Dans les sols fins en particulier, le mouvement de l’eau est influence ´ par les diffe ´rentes forces d’attachement de surface dues aux processus d’interface. Les effets d’interface ame `nent a ` plusieurs processus de relaxation die ´lectriques (phase aqueuse libre ou lie ´e, effet Maxwell–Wagner, effets de relaxation contre-ion). Ces processus de relaxation sont responsables de la forte de ´pendance de fre ´quence des proprie ´te ´s e ´lectromagne ´tiques d’un mate ´riau sous 1 GHz. Le potentiel de la matrice est une mesure des forces d’attachement sur l’eau contenue dans le sol. Selon une relation thermodynamique entre le potentiel de la matrice du sol et le comportement de l’eau en relaxation die ´lectrique dans diffe ´rents e ´tats de liaison, un mode `le a ` bande large de la relaxation die ´lectrique a e ´te ´ de ´veloppe ´ qui tient compte la dispersion a ` basses fre ´quences jusqu’a ` 1 MHz ainsi que des pertes dues a ` la conductivite ´ directe du courant. La sensibilite ´ du mode `le a e ´te ´ analyse ´e syste ´matiquement a ` partir d’une fonction de pe ´dotransfert (« PTF ») pour des sols ayant une texture variant du sable pur jusqu’a ` l’argile pure. Les re ´sultats sont compare ´s avec des fonctions de calibrage empiriques et semi-empiriques connues, ainsi qu’a ` des mode `- les the ´oriques de me ´langes. Mots-cle ´s : potentiel de la matrice du sol, spectroscopie die ´lectrique, re ´flectome ´trie dans le domaine temps (RDT), humi- dite ´ du sol. [Traduit par la Re ´daction] Introduction High-frequency electromagnetic measurement techniques are used to quantify spatial and temporal variation of soil moisture within scientific and practical issues of geotech- nics, hydrology, and soil physics (Rowe et al. 2001; Huis- man et al. 2003; Robinson et al. 2003; Lambot et al. 2004a; Drnevich et al. 2005; Evett and Parkin 2005; Kupfer 2005; Jaganathan and Allouche 2008). Precise knowledge of the frequency-dependent electromagnetic material properties is urgently necessary for successful utilization of these meth- ods (Shen et al. 1985; Ishida et al. 2000; Hilhorst et al. 2001; Cosenza and Tabbagh 2004; Heimovaara et al. 2004; Logsdon and Laird 2004; Logsdon 2005; Kelleners et al. 2005; Kupfer et al. 2007; Wagner et al. 2007c). However, in most applications this is not sufficiently taken into ac- count (Heimovaara et al. 2004; Hanafy and al Hagrey 2006; Kupfer et al. 2007). One promising technique to characterize a porous material like soil is based on the interaction between the dielectric properties of the soil phases and its textural, structural, and compositional properties (see Fig. 1). Probably the most im- portant drawback to model the soil dielectric properties in such a way is the complexity of the dielectric theory to Received 27 October 2008. Accepted 4 May 2009. Published on the NRC Research Press Web site at cgj.nrc.ca on 15 October 2009. N. Wagner. 1 Institute of Material Research and Testing at the Bauhaus-University Weimar, Coudraystr. 6, 99423 Weimar, Germany. A. Scheuermann. Institute for Soil Mechanics and Rock Mechanics, University of Karlsruhe (TH), Karlsruhe Institute of Technology (KIT), Engler-Bunte-Ring 14, 76131 Karlsruhe, Germany. 1 Corresponding author (e-mail: norman.wagner@mfpa.de). 1202 Can. Geotech. J. 46: 1202–1215 (2009) doi:10.1139/T09-055 Published by NRC Research Press Can. Geotech. J. Downloaded from www.nrcresearchpress.com by Shijiazhuang Railway College on 12/25/15 For personal use only.