The influence of matedness, roughness, and surface configuration of smooth to slightly rough joints on stress-dependent apertures

This study aims at answering an important question: Is the joint roughness coefficient ($JRC$) a suitable parameter for quantifying the hydro-mechanical behavior of smooth to slightly rough rock joints? To answer this question, we used 3D printing technology to produce matched and mismatched joints with the same surface configuration (profile) and joints with identical $JRC$ values but different surface configurations and measured the mechanical and hydraulic apertures ($E$ and $e$). A novel and straightforward approach for generating joint profiles with controlled joint surface roughness ($JRC$ = 3.5–5.8) was proposed, and the 3D-printed joint surfaces closely replicated target $JRC$ values. The stress-dependent $E$ and $e$ of printed joint samples with designed surface configurations and $JRC$ values were measured and fitted using semi-logarithmic closure model, revealing distinct trends for matched and mismatched joints. This study provides new insights into the applicability of the $JRC$ in predicting stress-dependent apertures, particularly by distinguishing its predictive value (variability) in matched versus mismatched joint with identical and dissimilar surface configurations. By decoupling the effects of matedness, asperity geometry, and roughness magnitude, the study demonstrates that while $JRC$ remains a reliable indicator for mismatched joints, it inadequately captures aperture variability in matched joints (within $JRC$ range of 3–5), where surface geometry and matedness dominate. This work not only provides a reproducible method for joint fabrication but also offers critical insights into the limitations of $JRC$ as a standalone descriptor, underscoring the need to incorporate surface configuration and joint matedness into future hydro-mechanical models.