Rock Mass Rating Calculator

This adds up a rock mass rating on Bieniawski's 1989 Geomechanics Classification, the version written RMR89. You give the intact rock strength, the RQD, the discontinuity spacing, the condition of the discontinuities, the groundwater condition and how the joints are oriented relative to a tunnel, foundation or slope, and it returns the basic rating, the adjusted rating and the rock mass class with its published stand-up time, cohesion and friction angle. An engineer assigns those parameters from core logs and mapped exposures, one structural region at a time. The class is an empirical guide, not a design.

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The condition of the discontinuities is taken from the summary descriptions in the main 1989 rating table.

Uniaxial compressive strength of an intact core piece. Below 25 MPa the 1989 table prefers UCS to a point load index.
Sum of core pieces 100 mm and longer, divided by the length of the run.
Mean spacing of the governing joint set, in millimetres.
Equivalent inflows per 10 m of tunnel are none, under 10, 10 to 25, 25 to 125 and over 125 litres a minute.
How the strike and dip of the governing set sit relative to the excavation.
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The 1989 guideline table splits the condition of the discontinuities into five sub-parameters and adds their ratings. Use this when the joint log records them separately.

Uniaxial compressive strength of an intact core piece. Below 25 MPa the 1989 table prefers UCS to a point load index.
Sum of core pieces 100 mm and longer, divided by the length of the run.
Mean spacing of the governing joint set, in millimetres.
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