Parameter conversion
Hoek–Brown to Mohr–Coulomb conversion
Why equivalent cohesion and friction angle are fitted parameters over a chosen stress interval—not unique material constants.
Core relationship
Fit τ = c′ + σ′ tan φ′ to the selected portion of the nonlinear Hoek–Brown envelope
Inputs & units
- Hoek–Brown parameters and σci
- Application-specific confining-stress range
- Fitting method and weighting
- Effective or total stress convention
Assumptions
- The numerical model requires a linear Mohr–Coulomb approximation.
- The selected stress range represents the application.
- The fitting approach and goodness of fit are reported.
Limitations
- It is an empirical rock-mass failure criterion, not a complete excavation, support or deformation model.
- Input quality, disturbance, anisotropy, groundwater, scale and stress-path effects may dominate the result.
- Any equivalent Mohr–Coulomb parameters depend on the selected confining-stress range and application.
- Changing the fitting interval changes c′ and φ′; a converted pair must not be reused outside its stated range without review.
Synthetic worked example
Synthetic comparison: fit the same nonlinear envelope over two different σ₃ ranges and report both parameter pairs and residuals. The difference is an expected consequence of linearization.
Engineering use boundary
This page is educational and supports preliminary assessment. It does not replace site investigation, competent engineering judgement, final design, independent review or permitting requirements.