Micro electrical resistivity tomography for seismic liquefaction study

This paper presents a laboratory experiment where electrical resistivity tomographies (ERTs), joined to surface monitoring with Laser Scanner, were acquired in time-lapse on a sandbox, subjected to impulsive shear strain. The experiment is an attempt to monitoring the different stages characterizing the hydro-geophysical status of a soil prone to liquefaction. During the experiment, strong 2D variations of resistivities, up to ±35%, were detected with small settlements measured at the surface. Resistivities variations are interpreted as condensation and water flow processes preparing the liquefaction of sand. This might be due to the impulsive shear strain, which caused liquefaction at the micro-scale, detectable with the time variation of resistivities, without liquefying the whole system. The results indicate that the combined approach using time-lapse ERTs and low energy seismic sources is suitable to follow the preparedness of soil to liquefaction by monitoring its hydro-geophysical status. This is promising to set up a geophysical methodology in the full-scale field to support geotechnical investigations in areas characterized by liquefaction hazard.