Ground Support Design Calculator

This calculator groups RMR into five discrete support classes rather than scaling continuously, and the entire 81-100 range falls into a single "Generally Unsupported" class -- no rock bolts are recommended anywhere in that band (bolt spacing and shotcrete thickness show 0 as a "not applicable" placeholder, not an actual spacing value). Once a rock mass crosses that top threshold, the model has no further reduction in support requirements to apply -- RMR 85 and RMR 100 produce identical figures.

Yes, and the bolt spacing figures move consistently with that: within Class V through Class II (RMR 0-80), bolt spacing widens as RMR improves -- 0.75 m, then 1.0 m, then 1.5 m, then 2.5 m -- because a wider spacing means fewer bolts per row, i.e. less support. The only place this looks like it reverses is the jump into Class I (RMR 81-100), where the reported spacing drops back to 0 m; that 0 isn't a tighter spacing than Class II's 2.5 m, it's a "no bolts needed" sentinel for the best-supported class of all. Read as bolt-count-per-row rather than raw meters, support strictly decreases as RMR increases across every class boundary.

Rock load scales directly with excavation span in this formula -- a wider opening is assumed to mobilize a proportionally taller zone of loosened rock above it, which increases the estimated load in direct proportion to span, holding RMR and rock density fixed. A wider tunnel or cavern therefore always carries a higher estimated rock load than a narrower one under otherwise identical conditions.

No -- it produces preliminary reference figures from a simplified RMR-to-support- class lookup and a simplified rock-load formula, not a substitute for a full geotechnical analysis. A qualified geotechnical engineer needs to verify ground conditions, review site-specific data, and finalize the actual support design before it's used for construction.