PSI - Issue 62

Stefano Stacul et al. / Procedia Structural Integrity 62 (2024) 185–192 Stefano Stacul and Nunziante Squeglia / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Standards/recommendations for nondestructive deep foundations testing: stress wave methods

Method

Reference

Title

Impulse Echo, Sonic Echo (IE)

NF P94-160-2 (1993) Institution of Civil Engineers (2016) ASTM D5882 (2016) NF P94-160-4 (1994) Institution of Civil Engineers (2016) ASTM D5882 (2016) NF P94-160-1 (2000) Institution of Civil Engineers (2016) ASTM D6760-16 (2017)

Sols: reconnaissance et essais - Auscultation d'un élément de fondation - Partie 2: méthode par réflexion

Specification for piling and embedded retaining walls

Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations

Impulse Response, Sonic Mobility (IR)

Sols: reconnaissance et essais - Auscultation d'un élément de fondation - Partie 4: méthode par impédance

Specification for piling and embedded retaining walls

Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundations

Cross-hole Sonic Logging (CSL)

Sols: reconnaissance et essais - Auscultation d'un élément de fondation - Partie 1: méthode par transparence

Specification for piling and embedded retaining walls

Standard Test Method for Integrity Testing of Concrete Deep Foundations by Ultrasonic Crosshole Testing Sols: reconnaissance et essais - Auscultation d'un élément de fondation - Partie 3: méthode sismique parallèle (M.S.P). Standard Test Methods for Measuring the Depth of Deep Foundations by Parallel Seismic Logging

Parallel Seismic testing (PS)

NF P94-160-3 (1993)

ASTM D8381-21 (2021)

3. Electrical Resistivity Tomography approach Previous methods are focused on deep foundations, nevertheless existing bridges are also supported by shallow foundations. Especially in this case, the identification of the foundation depth might be of extreme relevance, in fact, in many cases bridge piers are in the riverbed, thus the foundation could be exposed to scour. An alternative to nondestructive testing via stress wave methods is represented by the electrical resistivity tomography (ERT). The latter is a geophysical technique for identifying subsurface structures which consists in installing electrodes both for the generation of electrical currents and for the measurement of the voltage differential at the ground surface (or floating in water or within structures) around the investigated zone (Binley and Kemna, 2005). Pseudo-sections of the measured apparent resistivity as a function of the electrode spacing and location are generated and then an inversion process is applied to measured data for deriving the resistivity section of the investigated zone in which the intensity of the resistivity is plotted via contour maps with color scale. The latter represents the critical step of ERT method as there is not a unique solution, thus with the same measured data the final representation of the resistivity distribution might be different depending on the inversion settings (i.e., the constraints placed on the resistivity model during the inversion). This is due to the fact that resistivity is influenced by several parameters (i.e., saturation degree, material, fluid resistivity and temperature). The application of this method to the identification of unknown foundation and foundation depth of existing bridges is still limited but in recent years the number of cases reported in the literature has been growing (see as an example: Wang et al. 2013,2020; Wang and Hu 2015; Cardoso and Lopes, 2022) and the results are encouraging.