RS2 and CVBM spalling modelling: design takeaways for deep tunnel engineers
Reviewed by Joe Ashwell

First reported on Geoengineer.org – News
30 Second Briefing
Numerical modelling of deep underground excavations using RS2 and the Confinement-Dependent Visco-Plastic Model (CVBM) is used to capture spalling in jointed rock masses where confinement drops and tangential stresses concentrate around excavation boundaries. The approach contrasts brittle spalling in massive, low-porosity rock with more ductile behaviour in highly jointed rock, explicitly representing joint orientation, spacing, and strength. For design, this enables more realistic prediction of depth of failure, damage zones, and support demand around tunnels and caverns at high stress ratios.
Technical Brief
- RS2 finite-element models couple CVBM with explicit joint elements to simulate stress–damage interaction.
- Calibration uses laboratory triaxial tests and in situ stress measurements from deep underground case studies.
- Joint networks are parameterised by measured spacing, persistence and orientation sets rather than homogenised anisotropy.
- Time-dependent visco-plastic terms in CVBM capture delayed damage growth under sustained high tangential stress.
- Mesh refinement around excavation perimeters is required to resolve thin spalling slabs and notch geometries.
- Model outputs include evolving yielded zones, plastic strain localisation and predicted support load increments.
- Application to design focuses on optimising excavation sequencing and support installation timing in high-stress drifts.
- Scope is limited to hard, low-porosity rock masses; highly weathered or porous rocks are not addressed.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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