CIVE1105 Rock Mass Classification

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Author:
higgsboson
ID:
223986
Filename:
CIVE1105 Rock Mass Classification
Updated:
2013-06-25 09:04:27
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Classification Excavation Support
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Description:
Week 6 lecture notes summary. Exam
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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)
    • Mechanical excavation (TBM, partial-TBM, roadheader)
  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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