A Practical Method for Estimating the Volumetric Intensity of Non-persistent Discontinuities on Rock Exposures

The volumetric discontinuity intensity (\(P_{32}\)) is defined as the total discontinuity area by rock mass volume. \(P_{32}\) has been considered the most suitable parameter to quantify discontinuities within rock masses because it takes into account density and size and does not depend on orientation. Currently, determining the \(P_{32}\) from discontinuity mapping of rock exposures requires a series of discrete fracture network (DFN) simulations. This method is time-consuming and requires advanced software; thus, it is generally not used in practical rock engineering applications. This paper proposes a new method to obtain the \(P_{32}\) of rock masses from 2D rock exposures, based on well-known weighted joint density (\({\text{wJd}}\)) and mean trace length (\(\mu_{\text{l}}\)) estimates. The method was developed and validated using DFN modeling and compared with \(P_{32}\) estimates obtained by computational simulations in a real case study (Monte Seco tunnel). Finally, the synthetic rock mass (SRM) modeling technique was used to investigate the effects of \(P_{32}\) on the mechanical behavior of a hypothetical rock mass, highlighting the individual contributions of \({\text{wJd}}\) and \(\mu_{\text{l}}\). The results demonstrate that the proposed method is reliable and can estimate the \(P_{32}\) of rock masses without requiring computation simulations. Moreover, the SRM analysis showed that discontinuity density and size have a similar impact on the mechanical behavior of rock masses with non-persistent discontinuity sets.