Our team inspected McKay Power Station Headrace Tunnel and completed permanent repairs at both rockfall zones CH1980 & 2775 by installing new rock bolts and shotcrete lining.

Project snapshot:

• Access to the tunnel was restricted to the downstream end only, due to the intake structure being in the dam at the upstream end.
• This was further complicated by a valve house at the surface which made logistics the focus of the project.
• Our people and small equipment were brought in through an access hatch 2.4m diameter that was at 90 degrees to the tunnel.
• There was surge shaft located at CH 150 – this was only 2.6m diameter and 74m deep and only accessible via a tunnel 30m long, 3.65m high and 3.0m wide.
• Due to the head room restriction most of the equipment had to be disassembled lowered down and reassembled underground.
• Significant repairs to the invert floor where required from the CH1650 (Y-point) to CH2775 due to washing out.
• An estimated 700 tonnes of material was brought into level the floor allowing plant to reach the rockfall zones to repair them.

Completed work:

• Geological inspections, scaling and temporary support installations at:
  • Rocky Valley leg – CH166 (rock trap) to CH1963.
  • Rocky Valley leg – CH1985 to CH2791.
  • Rocky Valley leg – CH2802 to CH2810.
  • Pretty Valley leg – CH0 to CH60.
• Geological inspections, scaling and permanent support installations at:
  • Rocky Valley leg – CH1963 to CH1985.
  • Rocky Valley leg – CH2791 to CH2802.
• Geological inspections of incline section at:
  • Rocky Valley leg – CH4571 to CH4616.