Rock Mass Rating (RMR) Calculator – Free Bieniawski 1989 Tool
Rock Mass Rating (RMR) Calculator
Free online calculator based on Bieniawski 1989. Enter your parameters and get instant results.
✓ Bieniawski 1989✓ All 6 Parameters✓ Real-Time Results✓ PDF Download✓ 100% Free
1 Uniaxial Compressive Strength (UCS)
Determine from lab UCS test, point load index, or Schmidt hammer.
Rating0
2 Rock Quality Designation (RQD)
RQD = sum of core pieces >100 mm ÷ total core run × 100
Rating0
3 Spacing of Discontinuities
Rating0
4 Condition of Discontinuities (max 30)
4a. Persistence
4b. Aperture
4c. Roughness
4d. Infilling
4e. Weathering
Rating (capped at 30)0
5 Groundwater Conditions
Rating0
6 Discontinuity Orientation Adjustment
Adjustment0
—
Enter parameters above
020406080100
Basic RMR—
Orientation Adj.—
Total RMR—
Rock Class—
Description—
Stand-up Time—
Cohesion—
Friction Angle—
Parameter Breakdown
No data yet
RMR Classification Table
Bieniawski 1989 — Five rock classes with engineering properties
Class
RMR Score
Description
Stand-up Time
Cohesion
Friction Angle
I
81–100
Very Good Rock
20 yrs / 15 m
> 400 kPa
> 45°
II
61–80
Good Rock
1 yr / 10 m
300–400 kPa
35–45°
III
41–60
Fair Rock
1 wk / 5 m
200–300 kPa
25–35°
IV
21–40
Poor Rock
10 hrs / 2.5 m
100–200 kPa
15–25°
V
≤ 20
Very Poor Rock
30 min / 1 m
< 100 kPa
< 15°
How to Use This Calculator
7 simple steps — takes about 5 minutes with your field data ready
UCS: Run a lab UCS test, point load test, or Schmidt hammer. Select the matching strength range.
RQD: From core logs, add pieces longer than 100 mm and divide by total core run. Multiply by 100. Enter the percentage.
Spacing: Measure average distance between adjacent joints or bedding planes. Use the dominant discontinuity set.
Discontinuity Condition: Rate all five sub-parameters separately. Persistence, aperture, roughness, infilling, and weathering. The total caps at 30 automatically.
Groundwater: Observe conditions at the face or borehole. Rate conservatively if conditions change seasonally.
Orientation: Choose project type and rate how favorable joint orientation is relative to your excavation direction.
Results: Your score, class, and engineering parameters appear instantly. Click Download PDF to save a formatted report.
Tunnel Support by Rock Class
Primary support requirements — Bieniawski 1989
Class I — Very Good (81–100)
Generally self-supporting. Spot rock bolts only where required. Shotcrete not normally needed.
Class II — Good (61–80)
Spot bolts 3 m long at 2.5 m spacing. 50 mm shotcrete in crown if needed.
Class III — Fair (41–60)
Systematic 4 m bolts at 1.5–2 m. Shotcrete 50–100 mm in crown and walls.
Class IV — Poor (21–40)
4–5 m bolts at 1–1.5 m. Shotcrete 100–150 mm. Medium steel ribs at 0.75 m.
Class V — Very Poor (≤ 20)
Immediate face bolting. Heavy steel ribs at 0.5 m. Forepoling and grouting often required.
Frequently Asked Questions
Common questions from engineers, students, and site professionals
What is Rock Mass Rating (RMR)?+
RMR is a geomechanics classification system by Bieniawski (1973, revised 1989). It rates a rock mass on six parameters and produces a score from 0 to 100. Higher is better quality. It is the most widely used rock classification system in tunneling, mining, and slope engineering worldwide.
What is a good RMR score?+
Scores of 61–100 (Classes I and II) represent good-to-very-good rock that is largely self-supporting. Scores of 41–60 (Class III) are fair and need systematic support. Below 40 (Classes IV and V) requires heavy, immediate support.
How do I get RQD without core drilling?+
Use Palmstrom's formula: RQD = 115 − 3.3 × Jv, where Jv is the number of joints per cubic meter counted at a rock face. Alternatively, use Priest & Hudson (1976): RQD = 100 × e^(−0.1λ) × (0.1λ + 1), where λ is mean joint frequency per meter.
What is the difference between RMR76 and RMR89?+
RMR89 is the current industry standard. It has revised ratings for UCS and RQD, expands discontinuity condition into five sub-parameters, and updates the groundwater rating scale. Always use the 1989 version unless a project specifically requires the earlier edition.
How does RMR relate to the Q-System?+
Both are empirical classification tools. The common correlation is Bieniawski's (1976): RMR ≈ 9 × ln(Q) + 44. On important projects, calculate both independently and compare. Significant divergence signals unusual site conditions worth investigating.
What are the main limitations of RMR?+
RMR does not account for in-situ stress explicitly. It may overestimate quality in squeezing or swelling ground. The orientation adjustment is subjective. For highly stressed tunnels or very weak rock (UCS < 5 MPa), the Q-System or GSI may give better results.
Is this calculator suitable for professional reports?+
This calculator correctly implements Bieniawski 1989 and supports professional work as a computation aid. All input parameters must be assessed by a qualified geotechnical or mining engineer from actual field investigations and lab tests before use in final design.
Related Topics
Key areas of rock mechanics connected to RMR classification
Q-System (Barton 1974)
Uses six parameters including joint roughness, alteration, and stress. Widely used internationally for tunnel support design.
Geological Strength Index (GSI)
Developed by Hoek (1995). Estimates rock mass strength reduction from intact properties. Used in the Hoek-Brown failure criterion.
Rock Quality Designation (RQD)
Introduced by Deere (1963). The most universally collected rock quality index in geotechnical practice. Core parameter in both RMR and Q.
Slope Mass Rating (SMR)
Extends RMR for slope stability (Romana 1985). Adds correction factors for joint-slope orientation and excavation method.
Hoek-Brown Criterion
Empirical failure criterion for rock masses. Uses GSI, intact UCS, and mi constant. Converts to Mohr-Coulomb c and φ for design use.
Point Load Index (Is50)
Rapid field test for estimating UCS. Approximate conversion: UCS ≈ 24 × Is50. Useful when lab testing is not available on site.
Rock Mass Rating (RMR) — Essential Guide
What RMR Measures
RMR rates a rock mass — not just intact rock — using six field and lab parameters. It captures how joints, water, and orientation reduce practical strength below what a lab sample alone suggests. Score runs from 0 to 100. Higher means better quality, more stable ground, and less support needed.
The Six Parameters at a Glance
Parameter
Max Rating
What It Captures
UCS — Intact rock strength
15
Material strength from lab or field test
RQD — Core quality
20
Overall fracture intensity in the rock mass
Discontinuity spacing
20
How closely jointed the rock is
Discontinuity condition
30
Joint roughness, filling, weathering, aperture
Groundwater
15
Water pressure reduces effective strength
Orientation adjustment
0 to −12*
How joint geometry relates to the excavation
*Up to −25 for slopes. Orientation is the only parameter that can be negative.
RMR is standard practice in US transportation tunnels, transit systems, underground hydroelectric projects, hard-rock mining, and geotechnical reports submitted to FHWA, USACE, and state DOTs. It appears in Geotechnical Baseline Reports (GBRs) for major underground contracts as the primary rock quality descriptor.
RMR vs Q-System
RMR is easier to apply and communicate. The Q-System handles stress and joint condition in more detail. For most projects both are calculated and compared using: RMR ≈ 9 ln(Q) + 44. Significant divergence means the site needs closer investigation before finalizing support design.
Top Mistakes to Avoid
Averaging RQD across different rock types — always calculate RMR per geotechnical unit
Skipping the orientation adjustment — adverse joints can subtract up to 12 points in tunnels
Rating groundwater too optimistically — seasonal changes mean wetter conditions than drilling suggests
Using a single RMR value for design — run a sensitivity check on uncertain parameters