Monitoring processes in soil laboratory samples with 3D electrical tomography

The talk will focus on the use of Electrical Resistivity Tomography as an imaging tool for the investigation of the hydro-mechanical behaviour of soil samples.
In soil mechanics laboratory measurements are mostly performed from the boundaries of the soil samples, or anyway on a portion of sample that as a first approximation is assumed to behave homogeneously. Nevertheless, due to the inherent structure of the soil and to the non linearity of hydro-chemo-mechanical processes, several different phenomena can occur perturbing the assumed homogeneity (localization of mechanical strains, hydro-chemical dispersion, saturation – desaturation processes and so on). The interpretation of experimental evidences involving such phenomena is therefore complicated if measurements are taken in the traditional way.
The use of 3D electrical tomography therefore has been investigated, in a dedicated advanced hydro-chemo-mechanical cell, in a number of experiments, both to reconstruct initial heterogeneities (e.g. due to local variations of porosity or mineralogy) or to monitor transient processes in homogeneous and heterogeneous soil conditions.
Good results have been obtained for different phenomena such as mechanical consolidation, chemical diffusion and saturation changes. Preliminary exercises would suggest that the technique can be used in the quantitative characterization of sample properties, provided its association with numerical simulations of ‘multiphysics’ processes. This can be done by relating the soil electrical conductivity to structural and environmental soil conditions (porosity, water saturation and salt concentration in the pore water) by means of known transport laws.