Table 2.

Field characterization of rock mass conditions exposed at each turbine location

Turbine numberDepth to intact rock base and ledges*Rock strengthGSI characterizationRMR classification
T1Variable: at optimum location, intact fractured from 7.99 m depth; competent intact at 9 m below baseIntact rock characteristic strength based on testing and tactile assessment recorded as weak
  • Laboratory test: 21 MPa

Field appraisal:
  • Poor typically: 10 MPa

  • Moderate typically: 20 MPa

  • Good typically: 20–40 MPa

  • Poor to moderate: 50–65

  • Good: >65

No groundwater
  • Good = 70

  • Moderate = 49

  • Poor = 32

T2North area: highly variable and complex ground profile; significant proportion of pinnacled rockhead interface between excavation base and 8 m (described as very poor to moderate quality down to depths between 7.5 and 11 m and connected karst voids below ground to >40 mIntact rock characteristic strength based on testing and tactile assessment recorded as weak:
  • Laboratory test: 13–29 MPa

Field appraisal:
  • Poor typically: 10 MPa

  • Moderate typically: 20 MPa

  • Good typically: 20–40 MPa

  • Poor to moderate: 40–50

  • Good: >60

No groundwater
  • Good = 76

  • Poor = 27

South area: locally with large, poorly consolidated soil-infilled karst features to 16.5 m below turbine base; rock is poor to moderate quality down to depths between 16 and 22 m; with interposed soil-filled karst dissolution featuresIntact rock characteristic strength based on testing and tactile assessment recorded as weak becoming medium strong
  • Laboratory test: 13–29 MPa

Field appraisal:
  • Poor typically: 10–15 MPa

  • Good typically: 30–35 MPa

  • Poor to moderate (typical): 40–50

  • Good: >55

No groundwater
  • Good = 66

  • Poor = 60

T3Good to average rock at excavation base, of silicified dolomitic limestone; with depth below 2–3 m becomes moderate to locally poor; presence of soil-filled rifts bisecting base and single soil-filled karst pipe feature >40.5 m deepIntact rock characteristic strength based tactile assessment and in situ tests recorded as medium strong to strong ledge over weak:
  • Poor typically: 10–15 MPa

  • Good typically: 30–40 MPa

  • Poor to moderate (typical): 40

  • Good (shallow): >50

No groundwater
  • Good = 76

  • Poor = 74

T4Moderate to good rock extending from the excavation base, with variable zones of heavily fragmented rock encountered at horizons between 2 and 13 m depth; wide open soil-filled fissures bisecting the excavation were encountered locally, requiring excavation to extend onto good rock for ledgesIntact rock characteristic strength based tactile assessment and in situ tests recorded as medium strong to strong with zones of fragmentation:
  • Good typically: 15–55 MPa

  • Poor to moderate (fractured zones): 45

  • Good: >55

No groundwater
  • 0–5 m  >50

  • 5–8 m = 40

  • >8 m depth  >60

  • * Depth below foundation excavation base.

  • Based on tactile assessment of intact rock with occasional UCS testing, point load testing and Schmidt hammer tests.

  • For the various quality of rock recorded at each location.