Table 1

1 January 2000

Table 1: Guidelines for excavation and support of 10 m span rock tunnels in accordance with the RMR system (after Bieniawski, 1989).
Rock mass class Excavation Rock bolts (20mm, fully grouted) Shotcrete Steel arch
I - Very good rock RMR: 100-81 Full face, 3 m in advance. Spot bolting. - -
II - Good rock RMR: 80-61 Full face 1.5 m in advance, Complete support 20 m from face. Locally bolts in crown, 4 m long, 2.5 m spaced with occasional mesh wire. 5 mm in crown, in walls where required. -
III - Fair roock RMR: 60-41 Top heading and bench, 3-1.5 m advance in top heading. Commence support after each blast. Complete support 10 m from face. Systematic bolts 4 m long, 1.5 m spaced in crown and walls, with mesh wire in crown. 50-100 mm in crown, 30 mm in walls. -
IV - Poor rock RMR: 40-21 Top heading and bench, 1.5 -1.0 m in advance in top heading. Install support concurrently with excavation. Complete support max. 10 from face. Systematic bolts 4-5 m long, 1.5-1.0 m spaced in crown and walls with mesh wire. 100-150 mm in crown, 100 mm in walls. Light to medium rips, 1.5 m spaced where required.
V - Very poor rock RMR: <20 Multiple drifts, 0.5 - 1.5 m advance in top heading. Install support concurrently with excavation. Shotcrete as soon as possible after blasting. Systematic bolts, 5-6 m long, 1.5-1 m spaced in crown and walls with mesh wire, additional bolts in invert. 150-200 mm in crown, 150 mm in walls and 50 mm in front. Medium to heavy ribs, 0.75 m spaced, with steel lagging and fore poling if required, close invert.

Privacy Policy
We have updated our privacy policy. In the latest update it explains what cookies are and how we use them on our site. To learn more about cookies and their benefits, please view our privacy policy. Please be aware that parts of this site will not function correctly if you disable cookies. By continuing to use this site, you consent to our use of cookies in accordance with our privacy policy unless you have disabled them.