 Tunneling Quality Index Calculator
Tunneling Quality Index Q =(RQD/Jn)*(Jr/Ja)*(Jw/SRF) |
Table 1. Rock Mass Classification Based on RQD RQD | Rock Quality Classification | <25% | Very Poor | 25-50% | Poor | 50-75% | Fair | 75-90% | Good | 90-100% | Excellent |
Joint Set Number (Jn) DESCRIPTION | VALUE | Massive, No or few joints | 0.5-1.0 | One Joint Set | 2 | One joint set plus random | 3 | Two joint sets | 4 | Two joint sets plus random | 6 | Three joint sets | 9 | Three joint sets plus random | 12 | Four or more joint sets, "sugar cubes" | 15 | Crushed, Earthlike | 20 |
Joint Roughness Number (Jr) DESCRIPTION | VALUE | Discontinuous joints | 4 | Rough, Undulating | 3 | Smooth, Undulating | 2 | Slickensided, Undulating | 1.5 | Rough, Planar | 1.5 | Smooth, Planar | 1.0 | Slickensided, Planar | 0.5 | Thick infill - no rock contact | 1.0 |
Joint Alteration Number (Ja) DESCRIPTION | VALUE | | Tightly healed | 0.75 | | Surface Staining Only | 1.0 | | Low Friction thin coating (chlorite,talc,clay,etc) | 4.0 | | Thin Swelling Clay | 10.0 | | Thick Swelling Clay | 20.0 |
Joint Water Reduction, Jw | Joint Water Description | Pressure (kPa) | Jw | | Dry Excavation (Less than 5 litres/min locally) | <100 | 1.0 | | Medium Inflow or Pressure | 100-250 | 0.66 | | Large Inflow or High Pressure, No joint filling | 250-1000 | 0.5 | | Large Inflow or High Pressure, outwash of joint filling | 250-1000 | 0.33 | | Exceptionally large inflow or pressure, decaying after excavation | >1000 | 0.2-0.1 | | Exceptionally large inflow or pressure, no reduction after excavation | >1000 | 0.1-0.05 |
Stress Reduction Factor | Weakness Zone (If Present) | SRF | | Single shear zone in competent rock or single weakness zone containing clay and/or chemically disintegrated rock | 2.5 Excavation Depth > 50 m 5.0 Excavation Depth < 50 m | | Loose, open joints, heavily jointed, or "sugar cube" (any depth) | 5.0 | | Multiple shear zones in competent rock or Loose surrounding rock (any depth) | 7.5 | | Multiple occurrences of weakness zones containing clay and/or chemically disintegrated rock or Very loose surrounding rock | 10.0 | | Swelling rock - chemical swelling due to presence of water | 5-15 | | Squeezing Rock - Plastic flow of weak rock under stress | 5-20 |
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