Three-dimensional Electrical Resistivity Tomography to control the injection of expanding resins for the treatment and stabilization of foundation soils

Assessing subsoil void hazards along a road system using H/V measurements, ERTs and IPTs to support local decision makers

“…In the second step, considering the limited investigation depth and taking into account that the 2D‐ERT profiles were not as high performing in a complex environment with variations of water content and porosity changes (Fischanger et al ), 12 3D‐ERTs/IPTs were designed (Figure a). Using the 3D‐ERT acquisitions (Loke and Barker , Santarato et al ), it was possible (i) to arrange the electrodes along nonlinear profiles around buildings, residential lot boundaries, and all the other obstacle; (ii) to increase the investigation depth up to 30 –40 m; and (iii) to optimise the acquisition sequence to enhance the sensitivity inside the 3D‐ERT boundaries. Because of the logistical obstacles, only half of the 12 hypothesised that 3D‐ERT were actually carried out, whereas 11 3D‐ERT were designed and performed for a total of 17 3D‐ERT.…”

“…Given the dimensions of the sinkholes (some metres) and the hypothesis of a deep trigger phenomena (Intrieri et al , ), the electrode spacing was planned to be equal to 5 m. Unfortunately, due to accessibility issues, the electrode spacing varied from 1 to 5 m. After accounting for the advantages and limitations of each array configuration (Smith ; Loke and Barker ; Zhou et al ; Dahlin and Zhou ; Szalai and Szarka ; Santarato et al ; Samyn et al ), the pole–dipole array was employed for both 2D‐ERT and 3D‐ERT measurements. This array combines consistent signal strength with a high resolution and large depth of investigation (Santarato et al ). As is well known, the remote current electrode (B) has to be placed at a distance at least five times that of the largest A‐M distance for each survey (with A being the current electrode near the potential dipole M‐N).…”

“…The commercial software ErtLab TM (Geostudi Astier srl, Italy, and Multi‐Phase Technologies, USA) was employed to invert the ERT data. This software (i) employs finite‐element discretisation; (ii) implements an optimal data noise management (Cardarelli and Fischanger ; Fischanger et al ) for Occam’s regularisation (Constable, Parker and Constable ); (iii) has the ability to model the true remote electrode position by accounting for the effects of the B electrode when it is not placed at an appropriate “infinite” distance from the M‐N dipole (Santarato et al ); (iv) allows the exploration of the best electrode arrangements (i.e., the rotation of the electrode coordinates to achieve an electrode arrangement with a side as parallel as possible to the axis) to reduce mesh parametrisation; (v) calculates the quality of an inversion while accounting for every data point affected by the Gaussian noise (i.e., the error that affects the field data) and minimizing the misfit function between the field and modelled data, as defined in Santarato et al (); and (vi) allows setting a robust inversion to appropriately manage any noise during inversion by means of a data‐weighting algorithm that allows the adaptive changes of the variance matrix after each iteration for those data points that are poorly fit by the model. Therefore, the reliability of the model is not influenced by the shape of the loop.…”

L‐ and CORNER‐arrays for 3D electric resistivity tomography: an alternative for geophysical surveys in urban zones

“…), investigating the subsoil conditions beneath buildings (e.g., Trogu, Ranieri, and Fischanger ), and stabilization problems of foundation soils (Santarato et al . ). ERT‐3D was also exploited in archaeology, e.g., for prospection of tumuli (Tsourlos et al .…”

4D cross‐borehole electrical resistivity tomography to control resin injection for ground stabilization: a case history in Venice (Italy)

“…Seismic wave velocity distribution has been used to characterize the increase of the mechanical properties of consolidated soils (Foti and Lancellotta 2003) and of structures (Deidda and Ranieri 2005), both from surface-wave dispersion analysis (Dahlin et al 1999;Toohey et al 2010) and P-wave tomography (Rittgers et al 2010). As discussed by Santarato et al (2011), seismic methods do not appear adequate to manage and resolve a full 3D problem, in the reduced time compatible with field work procedures, while Ground-Penetrating Radar (GPR) cannot ensure the necessary penetration through clay-rich soils (Olhoeft 1986) and could penetrate below foundation walls only in favourable cases with timeconsuming multi-fold procedures (Fisher et al 1992).…”