Rock Mass Rating (RMR89) calculator

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Worked example — results

• ✓ Fair or better (RMR > 40)

Method, formulas and assumptions

• UCS rating = IF(80>250,15,IF(80>100,12,IF(80>50,7,IF(80>25,4,IF(80>5,2,IF(80>1,1,0)))))) = 7
• RQD rating = IF(65>90,20,IF(65>75,17,IF(65>50,13,IF(65>25,8,3)))) = 13
• Spacing rating = IF(0.4>2,20,IF(0.4>0.6,15,IF(0.4>0.2,10,IF(0.4>0.06,8,5)))) = 10
• RMR = Σ ratings + adjustment = 7+13+10+20+10+-5 = 55
• Class = IF(55>80,"I very good",IF(55>60,"II good",IF(55>40,"III fair",IF(55>20,"IV poor","V very poor")))) = III fair
• GSI ≈ RMR89 − 5 (dry, no adjustment) = 7+13+10+20+15-5 = 60

Related ground engineering calculators

• Point load index (rock) — Is and size-corrected Is(50) for diametral or axial/block tests, AS 1726 strength term and estimated UCS.
• Rock wedge stability (3-D, Hoek & Bray) with stereonet — Tetrahedral wedge formed by two discontinuities, the slope face and the upper ground surface. Geometry by…
• Rock slope kinematic analysis (planar, wedge, toppling) — Discontinuity sets mapped in a rock cut are tested against the slope face. Planar sliding needs a set…
• Q-system & support — Q = (RQD/Jn)(Jr/Ja)(Jw/SRF), equivalent dimension De = span/ESR, Q–RMR correlation and unsupported span.
• Hoek–Brown rock mass strength (GSI) — mb, s, a from GSI, mi and D; rock mass UCS, tensile strength, global strength and modulus.
• Joint shear strength (Barton–Bandis) — Peak shear strength τ = σn tan(φr + JRC log10(JCS/σn)) and equivalent friction angle.
• Block sliding / toppling criteria — Mode of a block of width b and height h on a plane of dip ψ with friction φ: stable, sliding, toppling or…
• Rock bolt pattern for a loose block / wedge — Bolt load from suspending a loosened zone of height h over the bolt tributary area, with bolt length guidance.