Indirect Estimation of Soil Shrink–Swell Susceptibility Using the Induced Polarization Geophysical Method

Induced polarization (IP) is based on the ability of a material to store electrical charges during the injection of a primary current. The accumulation and depletion of these charges decay once the primary current is shut off. As an extension of the electrical resistivity method, the joint acquisition of these two parameters (polarization and conductivity) enables a quantitative characterization of some petrophysical properties of soils such as the water content and Cation exchange capacity (CEC). Despite significant conceptual and technical advances, the validation of IP for the characterization of shrinking-swelling behavior of soils is so far limited. The goal of this study is to demonstrate how the IP method can be used to indirectly assess soil sensitivity to shrinking-swelling behavior. We compiled a dataset of 37 clay-rich soil samples collected from various sites in France affected by shrinking-swelling. For each sample, we measured IP, water content at saturation, CEC, methylene blue value (MBV), and Atterberg limits. The results show (i) a strong linear correlation between surface CEC measured from MBV (r² = 0.80) and from the cobalt-hexammine method (r² = 0.60); (ii) the validity of the dynamic Stern layer model for predicting CEC from IP and tested on a combined dataset of 529 samples from our study and from the literature; and (iii) the definition of optimal CEC thresholds (3.7 and 27 meq/100 g) derived from MBV and liquid limit sensitivity classes using a dynamic threshold optimization algorithm. In the context of increasing drought and flood frequency and intensity, these results pave the way for the development of a non-destructive, rapid, and spatially resolved characterization of soils susceptible to shrinking-swelling behavior.