Evaluation of Aereal Block Proportion (ABP) for the mechanical characterization of bimunits using Electrical Resistivity Tomography

The mechanical and technical characterization of bimunits (i.e., chaotic units consisting of hard blocks within a softer matrix), represents an untrivial challenge for researchers and practitioners. The main existing methods for their characterization require the estimation of the Volumetric Block Proportion (VBP). In real contexts, the VBP is typically estimated from point, linear, or areal measurements, making it strongly dependent on the availability of accessible outcrops and/or borehole data. To address this limitation, we evaluated the potential of geophysical (geoelectrical) methodologies for quantifying the Areal Block Proportion (APB) in bimunits. Specifically, we propose an approach for the analysis of electrical resistivity tomographies (ERTs) on bimunits, as outlined by Caselle et al. (2024). This approach is based on the fundamental research assumption that the electrical contrast between blocks and the matrix enables the discrimination of rock blocks in ERTs, provided their sizes exceed the resolution of the ERT. When block sizes are smaller, the ERT homogenizes the blocks-matrix mixture, producing an overall resistivity signature. This signature shows a positive proportionality with the percentage of blocks and can be used to estimate the ABP while still providing valuable information for bimunits characterization. This hypothesis was tested through numerical simulations and real ERTs, offering a preliminary validation of the proposed approach.  

 

Caselle, C., Comina, C., Festa, A., Bonetto, S. 2024. Electrical resistivity tomography for the evaluation of Areal Block Proportion (ABP) in bimunits: Modelling and preliminary field validation, Engineering Geology, 333, 107488, https://doi.org/10.1016/j.enggeo.2024.107488.