Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography

Abstract

In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposit.

Technical note: Application of geophysical tools for tree root studies in forest ecosystems in complex soils

“…2 and S4). Typically, belowground studies using GPR are carried out in sites with homogeneous soils, such as forest plantations, gardens, parks, backyards, crop fields, or under highly controlled conditions (Ow and Sim, 2012;Cermak et al, 2000;Cox et al, 2005;Dannoura et al, 2008;Zenone et al, 2008;Zhu et al, 2014) to reduce the difficulty in detecting and interpreting the origin of reflected signals (hyperbolic). In our case, it was fundamental to use high-and low-frequency antennas, as they gave valuable complementary information on these complex shallow rocky soils over volcanic bedrock.…”

“…With surface geophysical methods, such as electrical resistivity tomography (ERT), it is possible to monitor water content at soil-bedrock depths between 2.5 and 17 m and at frequent time intervals (Beff et al, 2013). ERT is a nondestructive, geoelectrical method to examine soil properties (Martinez-Pagan et al, 2013); it allows the generation of two-and/or three-dimensional images and maps depicting both the spatial and temporal variation in soil electrical conductivity, corresponding to variations in soil water content (Cosentini et al, 2012), and singularities like cracks and fractures (Travelletti et al, 2012). The resistivity of rocks and soil may vary depending on their water content, water salinity and mode of pore distribution, with a wide range of values (1-10 9 m −1 ); lower values indicate higher water content and vice versa (Orellana and Silva, 1982).…”

Evaluation of porosity and degree of saturation from seismic and electrical data

“…pressure plate extractor, suction controlled oedometer cell, filter paper method) (Fredlund & Rahardjo, 1993;Murray & Sivakumar, 2010). Recently Cosentini et al (2012) used electrical tomographic reconstructions in the laboratory to infer van Genuchten's parameters.…”

A combined use of Archie and van Genuchten models for predicting hydraulic conductivity of unsaturated pyroclastic soils

“…Many studies have shown that integrating geophysical and hydrogeological methods allows not only to obtain more accurate hydrostratigraphical models, but also to monitor hydraulic and geochemical processes (groundwater flow, solute transport, specific ion concentration) with high space and time resolution over a wide range of spatial scales (Breede et al, 2011;Campanella, 2008;Cosentini et al, 2012;Di Maio et al, 2013;Falgas et al, 2011;Nwankwoala and Udom, 2008;Ramalho et al, 2012). In particular, strong correlations between electrical conductivity and hydraulic conductivity are expected since they are both functions of the connected pore volumes and specific surface areas as well as of the saturation degree.…”