When a 200mm network watermain in South Auckland failed, utility company Watercare knew it had to act quickly.
The pipeline supplied drinking water to around 357 homes in the Glenbrook Beach region – an area experiencing rapid population growth.
But the pipe, which was anchored to the seabed, was subject to significant tidal influence. Over time, this compromised its integrity.
“The original pipeline experienced a joint failure that led to half a kilometre of pipe dislodging and floating to the surface of the Taihiki Estuary,” Watercare Design Manager Calvin McCluckie told Trenchless Australasia.
“This emergency prompted Watercare to establish a temporary solution, and subsequently, a permanent replacement project was conceived to ensure a resilient long-term water supply for the Glenbrook Beach area.”
A complex project
To deliver such an outcome, Watercare partnered with CDS New Zealand Ltd, an expert in horizontal directional drilling [HDD].
“The project was quite complex, entailing three parallel 750m crossings beneath the Taihiki Estuary,” CDS Engineer Marc Carmody said.
By engaging the services of Highside Drilling Services, CDS achieved added confidence in the pilot bore steering capability utilising the ParaTrack 2 guidance system.
Environmental features such as cliffs, as well as the length of the crossings, also forced CDS to think laterally. Rather than following the old pipeline alignment – which would have been the easy decision – CDS opted to chart a new and slightly longer alignment that kept the project clear of a cliff, keeping contractors and future maintenance workers safe.
“Another challenge we faced was the length of the crossing, which would have put more pull force on the relatively small bore pipe than we were comfortable with,” Carmody said.
“To remedy this, CDS calculated pipe pull forces and switched to a larger, non-typical pressure rating, PN25 pipe, which was strong enough to safely handle the crossing.”
Rising to the challenge, CDS mobilised to site in April, with the final crossing installed in early September. The company expects the pipeline to be operational by the end of October.
CDS ensured the project was suitably staffed and resourced including the establishment of its GoodEng HDD Maxi Rig, which provides a torque of 110,000 newton-metres with a maximum pull force of 3500-kilonewtons.
“It’s been refreshing having CDS as head contractor, as HDD specialists are usually called in as sub-contractors,” Carmody said.
“What made this project so effective was the early implementation of our team from the design phase, allowing us to be part of the geotechnical scoping work and for HDD to be designed into the project from the very start.
“This meant that potential risks were effectively identified and managed.”
Each crossing had its own unique ground conditions ranging from gravel to clay. The team was able to tweak their approach in each instance, keeping the project progressing smoothly.
CDS understands the importance of good HDD drilling fluid design. Using specialists, as well as its own experienced team, ensured the fluid properties were optimised for both hole cleaning function and to minimise circulating pressures, even as conditions changed downhole.
The HDD guarantee
Watercare Project Manager Sean McHenry knew HDD was the right tool for the job.
“HDD was selected for its ability to minimise environmental disturbance by allowing the pipeline to be installed deep beneath the estuary bed, reducing the risk of erosion and the likelihood of future pipeline failures,” he said.
“Additionally, since the Taihiki Estuary is popular among locals for water activities, HDD guarantees that the pipeline remains safely buried, eliminating the risk of damage from boat anchors or other activities that may have contributed to the previous pipe failure.”
McHenry also said that CDS’ ability to engage and work with other stakeholders was crucial in delivering the project.
HDD enabled CDS and Watercare to deliver a low-impact, environmentally friendly, and future-proof solution to the locals of Glenbrook Beach.
“This project is an investment in future of Glenbrook Beach, providing a resilient infrastructure that will support future growth and development in the region,” McHenry said.
For more information, visit cdsnz.co.nz
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