Rock Mass Rating Calculator

Enter rock mass data

The page uses a stacked section layout, while the input grid shifts to three columns on large screens, two on medium, and one on mobile.

UCS of intact rock (MPa)

Used for the intact rock strength rating.

RQD (%)

Rock Quality Designation from drilling or logging.

Discontinuity spacing (m)

Average spacing between significant discontinuities.

Discontinuity length / persistence (m)

Detailed condition factor.

Separation / aperture (mm)

Use 0 for tight or closed discontinuities.

Surface roughness

Another detailed condition factor.

Infilling / gouge

Represents filling material influence.

Weathering of wall rock

Used in the discontinuity condition subtotal.

Groundwater condition

Choose the closest field condition.

Excavation / project type

Controls the orientation adjustment scale.

Discontinuity orientation favourability

Pick the field-based orientation class.

Reset

Example data table

Example input	Sample value	Rating or note
UCS	120 MPa	Rating 12
RQD	78%	Rating 17
Discontinuity spacing	0.35 m	Rating 10
Persistence	2 m	Rating 4
Aperture	0.5 mm	Rating 4
Roughness	Slightly rough	Rating 3
Infilling	None	Rating 6
Weathering	Slightly weathered	Rating 5
Condition subtotal	4 + 4 + 3 + 6 + 5	22
Groundwater	Wet	Rating 7
Project type	Tunnels and mines	Orientation matrix applied
Orientation	Fair	Adjustment -5
Basic RMR	12 + 17 + 10 + 22 + 7	68
Adjusted RMR	68 - 5	63, Good Rock

Formula used

Basic RMR = UCS rating + RQD rating + spacing rating + discontinuity condition rating + groundwater rating

Adjusted RMR = Basic RMR + orientation adjustment

Discontinuity condition rating = persistence rating + aperture rating + roughness rating + infilling rating + weathering rating

The calculator first converts field and laboratory observations into ratings. It then sums the first five parameter scores to obtain the basic RMR. A final adjustment is added for discontinuity orientation, based on the chosen project type and favourability class.

RMR is an empirical design aid. Always confirm excavation support, groundwater response, and stability decisions with site-specific investigation, mapping, testing, and engineering judgment.

How to use this calculator

Enter the uniaxial compressive strength of the intact rock in MPa.
Enter the Rock Quality Designation as a percentage from core logging.
Add the average discontinuity spacing in meters.
Fill the five detailed discontinuity condition inputs: persistence, aperture, roughness, infilling, and weathering.
Select the groundwater condition that best matches the site.
Choose the project type, then select the joint orientation favourability category.
Press Calculate RMR to show the result card above the form.
Review the summary, graph, and class interpretation, then export the report as CSV or PDF.

FAQs

1) What does the rock mass rating number mean?

It is a combined engineering index that summarizes rock quality. Higher values generally indicate better rock mass conditions, while lower values suggest more fractured, weaker, wetter, or less stable conditions.

2) Why is orientation handled separately?

Orientation can strongly affect excavation performance even when the rock mass is otherwise similar. This is why the calculator first computes a basic score, then applies a project-specific orientation adjustment.

3) Can I use this for tunnels, slopes, and foundations?

Yes. The calculator includes separate orientation adjustment scales for tunnels and mines, foundations, and slopes. Choose the project type that matches the engineering case you are reviewing.

4) What is the difference between basic and adjusted RMR?

Basic RMR uses the first five rating groups only. Adjusted RMR adds the orientation effect. The adjusted result is the final value typically used for classification in this page.

5) Why are condition inputs broken into five parts?

That approach provides a more detailed assessment of discontinuity condition. Persistence, aperture, roughness, infilling, and weathering each influence shear behavior and block stability differently.

6) Does this replace site investigation or support design?

No. It is a structured screening and reporting tool. Final excavation support, stability checks, and construction decisions still require field mapping, laboratory testing, and engineering judgment.

7) What if my field values are between two categories?

Use the category that best matches the mapped condition, or compare both nearby cases to see sensitivity. Engineering context matters, especially where groundwater or adverse structure controls behavior.

8) What can the CSV and PDF exports be used for?

They are useful for design notes, internal reviews, field reports, or sharing with colleagues. The export captures the current calculation inputs, ratings, and final classification summary.