# CIVE1105 Rock Mass Classification

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 Author: higgsboson ID: 223986 Filename: CIVE1105 Rock Mass Classification Updated: 2013-06-25 09:04:27 Tags: Classification Excavation Support Folders: Description: Week 6 lecture notes summary. Exam Show Answers:

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1. Rock Mass Classification Systems
• • Rock Quality Designation (RQD)
• • Geological Strength Index (GSI)
• • Bienawaski's Rock Mass Rating (RMR)
• • Q-System
2. RQD values
• The percentage of intact core pieces longer than 100mm (4 inches) in the total length of core.
• Very Poor 0-25%
• Poor 25-50%
• Fair 50-75%
• Good 75-90%
• Excellent 90-100%
3. RQD =
4. GSI
• Determines strength of a jointed rock mass according to properties of intact rock pieces and the freedom of those pieces to slide and rotate under different stress conditions.
• See p4 Week 6 lecture notes.
5. RMR
• • Intact Rock Strength UCS (15 pts)
• • RQD (20 pts)
• • Mean Joint Spacing (20 pts)
• • Joint Condition (30 pts)
• • Groundwater conditions (15 pts)
• Sum all conditions and  then adjust for orientation of joints with respect to the tunnel.
• See p7 Week 6 lecture notes.
6. Q System
• RQD Rock Quality Designation
• Jn joint set number
• Jr joint roughness number
• Ja joint alteration number
• Jw joint water reduction factor
• SRF stress reduction factor
7. Correlation between classification indices
• GSI = RMR - 5
• GSI = 9lnQ+44
• sigma
8. Q system, ESR
• Excavation support ratio
• A Temporary mine openings. 3-5
• B Permanent mine openings, water tunnels for hydro power (excluding high pressure penstocks), pilot tunnels, drifts and headings for large excavations. 1.6
• C Storage rooms, water treatment plants, minor road and railway tunnels, surgechambers, access tunnels. 1.3
• D Power stations, major road and railway tunnels, civil defence chambers,portal intersections. 1.0
• E Underground nuclear power stations, railway stations, sports and public facilities, factories. 0.8
9. Tunnel Support Design
Most widely used classifications
• Q System Barton et al. (1974)
• Rock Mass Rating (RMR)
10. Excavation in rock. Methods
• Blasting (bulk, pre-split, drill & blast)
11. Stabilisation strategy
• Rock Reinforcement (insert bars, roads or cables to stiffen rock mass)
• Continuous medium; behaves as reinforced composite material. Discontinuous medium; behaves as stiffer & stronger continuous medium.
• OR
• Rock support (use of structural elements to inhibit rock mass displacement)
• Continuous medium; inhibited displacement of continuum. Discontinuous medium; inhibited displacement of individual blocks.
12. Rock Reinforcement / Rock Support
13. Rockbolting
Installation of systematic rockbolts helps to create a zone of compression on
the roof, forming a self-supporting arch.

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