Application of the point counting technique for estimating the VBP of geotechnically complex formations (bimrocks/bimsoils)

The estimation of the Volumetric Block Proportion (VBP) of geotechnically complex block-in-matrix formations (such as melanges) is crucially important for reliable predictions of their mechanical behavior, and for reducing safety risks and extra costs caused by unexpected technical problems that can occur during excavation/construction works. However, estimating site-scale VBPs is extremely difficult. This paper describes a statistical investigation of virtual block-in-matrix models to determine the amount of bias introduced when the point counting technique is used to infer VBPs from in-situ 0D (point) measurements (PBP). A graph is provided to obtain an uncertainty factor (UF) to adjust the measured PBPs to real VBPs, on the basis of the block content measured and the size of the area analyzed. To validate the approach, the results are compared to those provided recently by Napoli et al. (2020), where the uncertainty in estimates of VBPs from 2D measurements was investigated.