One of the most challenging HDD installations ever attempted in NZ in regards to geotechnical variance and distance. Installed approx. 10km of pipework and power in 3km of HDD bores. Bore holes ranged in size from 350mm to 600mm diameter and pipe diameters ranged from 225mm to 400mm OD. All shots were drilled in solid rock ranging from silt stone highly contaminated with lignite coal seams through to extremely hard solid rock with quartz boulder seams. 3 parallel shots were undertaken which crossed under the Mataura River, Waikaka River and a main road in continuous 600m lengths.
The Mataura River shots consisted of 2 vertical alignment and 1 horizontal alignment change all the shots crossed under one another to exit in a straight line down the road berm opposite the Waikaka River. Total depths ranged up to 16m. 8 further parallel installations were undertaken up river to connect the factory, they were all continuous compound curves. Recycled fluid system consisted of 100,000 litres of circulated mixed metal oxide mud which was pumped back to the rig from pipe side by a mud return line also installed under the river. Flow and processing rates averaged around 2,000 litres per minute. Major ground entry works were required to enable access to the bedrock layers through a historic HAIL site, 8m of running shingle, boulders and ground water. These works included constructing solid concrete corridors and washing in an 800mm diameter steel casing with the maxi rig.
Hadlee & Brunton with MJS undertook all of the design and engineering required for the project.
