Our team worked with AGL via Early Contractor Involvements (ECI) to complete the repair of a partial tunnel collapse at CH2035 of the Bogong Headrace Tunnel in Victoria on the back of the great performance completed on the McKay Headrace Tunnel Repair.

Project snapshot:

• Due to access restrictions downstream caused by the Headrace Access Tunnel (HAT) Hatch or submarine door, (1.6m height and 1.3m wide) it was decided early in the project to approach the defect from both ends.
• Smaller plant was disassembled and tracked through the submarine door while larger plant was lifted in via the upstream shaft at McKay Power Station (MKPS) Headpond.
• This had its own challenges as access was via a 5m diameter shaft by 140m deep and then a 4.5km journey over a rough invert that need repairing along the way.
• People access was restricted under the defect however we put in place the necessary equipment to allow limited access from both ends via the submarine door downstream and with a crane and manbox upstream.

Completed works:

• Permanent repairs at the defect CH2023 to 2031 (exact).
• Temporary invert repairs upstream of the defect to enable plant access.
• Installation of temporary support at various locations upstream of the defect as determined by Tunnelling Solutions and geotechnical inspections.
• Cut out and installed a steel sump lining in the rock trap for smoother operation of pumps.