The Auckland suburb of Birkdale had been prone to wastewater overflow during heavy rain, leaving residential properties and streets flooded with wastewater.

To alleviate the flooding, the North Shore City Council near Auckland established Project Care, which included a new large diameter pipeline under densely populated urban areas.

The construction contract for the Birkdale B portion, which included a continuous 1,030 m section of pipe installed at a depth of up to 30 m, was awarded to Pipeworks in December 2009. Drilling commenced in February 2010 and was successfully completed in December the same year.

Setting the record

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During construction, a New Zealand distance record was set for the 1,030 m continuously drilled shot. This was the first time an installation in a single shot greater than 1,000 m had been achieved in New Zealand.

Along the way to this record, numerous challenges were faced and overcome, including a very shallow gradient (as low as 0.5 per cent), a highly-curved alignment and difficult soil conditions (alternating between soft clay and sandstone) all through an exceptionally sensitive environment.

FPVC pipe benefits

Although originally a 630 mm polyethylene pipe was specified, Pipeworks believed a number of technical difficulties could be minimised by using a 550 mm fusible PVC (FPVC) pipe. This was the first application of FPVC in the Australasian region and was supplied by Iplex Pipelines.

The superior tensile strength and hydraulic capacity of relatively thin-walled FPVC pipe reduced construction risks and provided economic benefits. Because FPVC requires a small diameter bore, the pulling force necessary to complete the task was reduced, and drilling mud usage and spoil disposal was minimised.

Pipeworks opted to use a Paratrack system to track the pilot bore drill head. The combination of a mud motor and the novel Paratrack system had never been attempted before in New Zealand, but proved highly successful. The drill head was tracked with surgical precision and the deviation in alignment over the 1,030 m in length at up to 30 m depth was never more than 100 mm.

Ecologically minded

During works, Pipeworks liaised with Kaipatiki Ecological Restoration Group, who preserve and protect an adjacent nature reserve. A mutually rewarding relationship resulted in Pipeworks leaving its newly-built construction road in place for future use.

Pipeworks won the New Zealand Contractor’s Federation Environmental Award in 2011 for the project. The company is very proud of the environmental outcomes realised and for establishing the New Zealand record for a single directional drill shot.

The project lead to Iplex and Pipeworks securing the technology licence to manufacture and fusion-weld FPVC pipe in New Zealand and Australia, opening opportunities for drilling contractors and pipeline owners to benefit from reduced excavation costs and longer pulls with lower construction risk.