Underground Ground Support

The rock mass rating system after Bieniawski 1989, printed in three places on this shelf and cross-checked between them: SME Mining Engineering Handbook, 3rd ed. Table 8.4-6, p. 536; SME Mining Reference Handbook, 2nd ed. Table 14.3, p. 333; and SME Mining Reference Handbook, 1st ed. Table 13.2, p. 244. All three agree on every rating.

Three printings, not three authorities. Two of those are successive editions of the same reference handbook, so this is a weaker claim than three unrelated books and it is worth stating plainly rather than letting the count do the talking. It is still a real check: the editions are separately typeset, they were separately transcribed here, and a disagreement between them is exactly what found the error below.

One disagreement, resolved. Table 14.3 p. 333 prints the middle spacing band as “2–600 mm”. It should read 200–600 mm, which is what the other two books print, and the band sequence settles it on its own: >2 m, 0.6–2 m, 200–600 mm, 60–200 mm, <60 mm is descending and contiguous, while “2–600 mm” would swallow the band below it. That is an error in the printed page rather than in our reading of it, so this page uses 200–600 mm.

SME Mining Engineering Handbook Table 8.4-4, p. 532, adapted from Hoek and Brown 1997. The seven field terms map one for one onto the seven strength bands the rating uses, which is why picking one in Step 1 can fill the box rather than just hint at it.

SME Mining Engineering Handbook Table 6.2-7, p. 351, as a sanity check on what the hammer told you. Published in both MPa and psi, and the two agree: 41.3 MPa against 6,000 psi is 41.37, 137.9 against 20,000 is 137.90, 206.8 against 30,000 is 206.84. Note these are broad rock-type bands and a weathered example of any of them sits lower.

Bieniawski 1979, printed identically in the SME Mining Reference Handbook at 2nd ed. p. 335 and 1st ed. p. 245. Two separately typeset editions, separately transcribed here, agreeing number for number. Not two independent authorities, but a genuine check on the reading of both.

Read the basis before you use it. Both books print the same one: a horseshoe profile, 10 m wide, vertical stress below 25 MPa, driven by drill and blast, and both add that the table is a guide only. A 5 m heading is not a 10 m tunnel, and this page tells you when your span, stress or profile has walked away from that basis instead of quietly scaling the pattern as though it had not.

SME Mining Reference Handbook, 2nd ed. Table 14.3 D, p. 334. Stand-up time is quoted against a specific span, and the spans differ by class, so it is not a number you can carry across to your own heading without checking the span it belongs to. This page compares the two for you rather than interpolating between them, because the source publishes five points and no curve.

SME Mining Engineering Handbook, p. 617, typical Split Set properties, courtesy of Mansour Mining. Shown because bolt length is one of the two numbers this page hands you and the hardware has to exist in that length: the shorter sets stop at 2.4 m and only the largest reaches 3.7 m, so a guideline calling for 5 to 6 m bolts in very poor rock is calling for a different product entirely. The guideline table itself is written for 20 mm fully grouted bar, not friction sets.

A coal-entry roof bolt capacity table also sits in the corpus and is deliberately NOT used here: its capacity column carries no unit on the printed page, and coal entry support is a different problem from a hard-rock tunnel.