Design and Build Contract for the HDD installation of a 550m long 355mm SDR11 PE100 pumping main under the Heathcote River and major Dyers / Ferry / Tunnel Road roundabout. This project was the final section of the Lyttelton Wastewater Scheme. Once completed, all of Lyttelton’s and Diamond Harbour’s wastewater will be redirected to the main Christchurch wastewater treatment plant in Bromley.

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. 

Pan Pac Forest Products Limited is one of New Zealand’s largest timber pulp mills and they pump tens of thousands of litres of consented, treated waste water from their plant out to sea via a 2.5 km outfall pipeline. The pipeline which was 400mm dia steel encased in a 50mm concrete shell, failed in the surf zone approx. 3m deep in running shingles. Repairs from the outside were attempted but resulted in a sheet pile being punched through the existing steel pipeline filling the pipeline with sea water, running shingles and causing large metal rips / tags to be bent into the pipeline. To add to the complications the pipeline could only be shut down for 8 to 10 hours per day, any longer than this and the factory would have to shut down at a cost of $1,000,000.00 per day. The discharge into the surf zone in front of residential homes had also created national TV media exposure and the threat of abatement notices from councils.

The scope included relocating the main gas feed line to Wellington to enable a new bridge to be installed on State Highway 1. H&B completed the initial HDD design, feasibility and engineering works for the client which involved installing 700m of 250mm diameter steel gas main in one continuous length under the Manawatu River. 

Installed 1.8 kilometres of 300mm and 200mm dia. steel gas main. The twin lines were installed four metres apart, at depths of up to 15m and on mirrored compound curved alignments in very challenging ground conditions. The alignments passed under multiple high-risk elements such as rivers, highways and buildings all during the same shot. Installed a 710mm dia. PE stormwater pipe to a critical grade of 0.3%. Installed 500m of multiple ducting clusters for communication & power services on compound curves and in parallel alignment. All installations were undertaken using the Herrenknecht maxi rig & MPR recycling unit. Engineering and design work assistance by MJS.