Between 1997 and 2002 DHML was contracted by Meridian Energy to excavate a tailrace for the 2nd Manapouri Power Station tunnel plus associated site works, for $3.5M.
The 2 stage contract required construction of a new tail race and widening of the existing tail race with flows up to 450 cumecs, and required excavation to 7m below water-level:
Stage1: Site clearing and setting up dump sites, portal earthworks for site facilities, and Tunnel Boring Machine entrance, and associated river control works.
Stage 2: Tailrace construction and widening.
As part of Stage 2, a 160 tonne digger was fitted with an extended boom and dipper arm with 23 metre reach. A 3D survey system was developed in conjunction with Geosystems Ltd for all in-water work. A digital terrain model of the job was loaded into the ‘on-board’ laptop and compared with the position of the bucket, giving real-time information on cut or fill profiles. Tolerances for cut-to-grade and placement of rip-rap were +/- 125mm. As-builts were recorded as work progressed.
Work was completed 15 days ahead of schedule with no quality or environmental non-conformances.
This completed contract was joint winner (1 of 3) of Category 2 – (Contracts $1.0M to $1.5M), 2002 NZ Contractors Federation Caltex Construction Awards.
This contract was also winner of both the Innovation Award & the Environmental Award, 2002 Canterbury Contractors Federation Mobil-Goughs Contractor of the Year Awards.
Volumes moved included:
25,100 m3 above water
102,800 m3 below water
8,100 m3 rip-rap