Should JRC be used to assess rock joint hydro-mechanical behavior? Perspectives derived from 3D-printed joint aperture measurements

Abstract

The objective of this investigation is to address a critical inquiry: Is the joint roughness coefficient (JRC) an appropriate metric for assessing the hydro-mechanical behavior of smooth to slightly rough rock joints? We employed 3D printing technology to create matched and mismatched joints with similar surface configurations (profiles) and joints with the same JRC values but varying surface configurations, subsequently measuring the mechanical and hydraulic apertures (E and e). A new and easy way to make joint profiles with regulated joint surface roughness (JRC = 3.5–5.8) was suggested, and the 3D-printed joint surfaces were very near to the required JRC values. The stress-dependent E and e of 3D-printed joint samples with defined surface configurations and JRC values were measured and fitted using a semi-logarithmic closure model, demonstrating unique trends for matched and mismatched joints. This research elucidates the application of the JRC in forecasting stress-dependent apertures, specifically by differentiating its predictive efficacy (variability) in matched versus mismatched joints with both identical and divergent surface configurations. The study decouples the effects of matedness, asperity geometry, and roughness magnitude, demonstrating that while JRC is a reliable indicator for mismatched joints, it inadequately reflects aperture variability in matched joints (within the JRC range of 3–5), where surface geometry and matedness are predominant factors. This study not only presents a reproducible technique for joint construction but also elucidates the limitations of JRC as an independent descriptor, highlighting the necessity to integrate surface configuration and joint matedness into forthcoming hydro-mechanical models.