A critical analysis of the performance of plate- and point-electrodes for determination of electrical properties of the soil mass S.U. Susha Lekshmi a , Prathyusha N.V. Jayanthi a , P. Aravind b , D.N. Singh a,⇑ , Maryam Shojaei Baghini b a Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India b Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India article info Article history: Received 7 September 2015 Received in revised form 13 July 2016 Accepted 15 July 2016 Available online 17 July 2016 Keywords: Soil mass Sensors Measurement Impedance spectroscopy Simulation COMSOL Multiphysics Ò abstract In the recent past, researchers have started utilizing electrical properties of the soil mass for its charac- terization by employing either plate- or point electrodes. Though, plate-electrodes are easy to use for lab- oratory experiments, and quantification of geometrical characteristics of the electric field generated within them is easy to quantify, their application for in-situ experiments and for samples of cylindrical shape becomes difficult. On the other hand, usage of point-electrodes which are cylindrical in shape, are used for moisture content determination of the soil or migration of contaminants in it, for coarse- grained soils and fine-grained soils might yield erroneous results, due to the presence of inter particle voids and presence of cavities & anomalies, respectively. Furthermore, quantification of geometrical parameters of the electric field of point-electrodes is quite difficult which results erroneous measure- ments in determination of electrical properties of the material, in which they are installed. Hence, estab- lishment of the uniqueness of electrical properties obtained from the plate- and point-electrodes, for identical samples becomes utmost important. With this in view, COMSOL Multiphysics Ò was employed to simulate the electrical response of various geomaterials in their uncontaminated and contaminated states and results were critically evaluated vis-à-vis those obtained from the impedance analysis (1 Hz to 40 MHz). Efforts have also been made to relate the geometrical dimensions of electrodes and electric field generated across the point electrodes, which would facilitate proper design and installation of sen- sors in a material to achieve the desired output. This study demonstrates the suitability and versatility of the point-electrodes for various (field and laboratory) applications where in moisture profiling and con- taminant transport is to be established. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Electrical properties of the soil mass such as dielectric constant [1–3], electrical conductivity [4–6], electrical dispersion [7,8] and impedance [9,10] have been utilized for determining its volumetric moisture content [1,3], degree of saturation [11,12], degree of com- paction [13], porosity [14], permeability [15,16] and fabric struc- ture [7,9,17]. A few other real life applications wherein these properties play an important role are: detection of the ground water contamination [18], subsurface water profiling [19,20], detection of frozen soils [21] and estimation of soil salinity and conductivity [6,22]. The dielectric constant, k, a measure of the ability of a material to store electrical charges under the influence of an electric field, is influenced by both ion concentration and types of ions present in it. Hence, its effect on the soil behavior, especially soil-water sys- tem has utmost importance [2,23,24]. Incidentally, researchers [1,6,25,26] have correlated k with volumetric moisture content, h, based on the fact that for the dry soils, k ranges between 2 and 8, while for pure water its value is 81. The electrical conductivity, r, a measure of charge mobility within a material due to the appli- cation of electric field, is another important parameter that can be employed for the soil mass characterization. In this context, earlier researchers [5,27–30] have correlated r of the soil mass with its h, conductivity of pore solution, clay content of the soil and its min- eralogy. Incidentally, Gumaste et al. [31] have employed ‘aniso- tropy coefficient’, which is the ratio of electrical conductivities of the soil mass in the transverse and longitudinal directions, for quantification of the grain orientation and fabric anisotropy. http://dx.doi.org/10.1016/j.measurement.2016.07.052 0263-2241/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: sushalekshmi@iitb.ac.in, sushalekshmi.su@gmail.com (S.U. Susha Lekshmi), 123040016@iitb.ac.in (P.N.V. Jayanthi), aravindp@ee.iitb.ac.in (P. Aravind), dns@civil.iitb.ac.in (D.N. Singh), mshojaei@ee.iitb.ac.in (M.S. Baghini). Measurement 93 (2016) 552–562 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement