Rock-mass characterization
Geological Strength Index (GSI)
GSI describes rock-mass structure and discontinuity surface condition for use in estimating Hoek–Brown rock-mass parameters.
Core relationship
GSI → mb, s and a within the generalized Hoek–Brown framework
Inputs & units
- Rock-mass blockiness or structure
- Discontinuity surface condition
- Mapped domain and scale
- Disturbance context where relevant
Assumptions
- The rock mass is suitable for GSI characterization.
- The estimate is tied to observed structure and surface-condition descriptions.
- A range is retained when observations do not justify a single value.
Limitations
- GSI is not a direct strength measurement.
- Simple universal conversion such as GSI = RMR − 5 is not appropriate without checking the original conditions.
- Highly anisotropic, structurally controlled or weak-rock conditions require method-specific judgement.
Synthetic worked example
Synthetic workflow: record the geological observations first, select a justified GSI range second, and propagate the range through the strength estimate rather than presenting false precision.
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.