Strength criterion
Hoek–Brown criterion
A transparent introduction to the empirical rock-mass strength criterion, its inputs and the boundary between a preliminary calculation and an engineering design decision.
Read method →Methods · comparisons · workflows
Technical method library
Find formulas, inputs, units, assumptions, limitations, worked examples and primary references before deciding whether a method fits your question.
8 technical pages
Rock-mass classification
Rock Mass Rating
RMR combines ratings for intact strength, RQD, discontinuity spacing and condition, groundwater, and an orientation adjustment into a rock-mass classification.
Read method →Rock-mass classification
Q-system
The Q-system characterizes rock-mass quality with six parameters and links Q and excavation dimensions to empirical support guidance.
Read method →Rock-mass characterization
Geological Strength Index
GSI describes rock-mass structure and discontinuity surface condition for use in estimating Hoek–Brown rock-mass parameters.
Read method →Analytical stress solution
Kirsch tunnel stress
Explore the closed-form elastic boundary stress around an unsupported circular opening under biaxial far-field stress, with the convention and scope shown beside the result.
Read method →Parameter conversion
Hoek–Brown to Mohr–Coulomb
Why equivalent cohesion and friction angle are fitted parameters over a chosen stress interval—not unique material constants.
Read method →Method selection guide
RMR vs Q vs GSI
A practical comparison of three related but non-interchangeable systems: what each describes, what it needs and what it should not be asked to decide.
Read method →Workflow guide
Preliminary tunnel assessment
A staged, reviewable route from input provenance through analytical checks, rock-mass characterization, sensitivity and explicit escalation criteria.
Read method →Review habits worth keeping
Spreadsheet vs traceable workflow
A spreadsheet can calculate correctly yet lose review context. Keep source, unit, assumption, version and warning with every reusable case.
Unit errors in geotechnical calculations
Treat every value as value plus unit. Convert at system boundaries and display the unit used in every result.
How to verify an engineering calculation
Start with closed-form benchmarks, edge cases and independent reference values; validation of intended use is a separate step.
When an analytical method is insufficient
Escalate when idealized geometry, continuum behaviour, elastic response or boundary conditions no longer represent the controlling mechanism.
Documenting assumptions
State the assumption, evidence, expected influence, uncertainty and the condition that would invalidate it.