As part of ongoing works for the installation of new infrastructure, renewal of existing infrastructure in locations with high stakeholder requirements, demanding traffic management needs and situations where trenched installation is difficult, Christchurch City Council in New Zealand recently utilised the horizontal directional drilling services of Utilities Infrastructure New Zealand Ltd (UNIZ) for installations on its Southshore Water Main Renewal project.
Given that there exists a large and diverse range of operating conditions across New Zealand, HDD was selected as the best option for these works, not least because locally the ground conditions comprised a shallow ground water table, at between just 1 to 300 mm depth and running sands. These conditions made the use of traditional excavation methods near impossible. HDD therefore also provided significant cost and time savings.
For the Southshore Water Main Renewal project, UNIZ decided to utilise its Vermeer Navigator 3650 drill rig which was supported with a range of Melfred Borzall down hole tooling from the sonde housings to the Turbo Reamer that was to be used in the sandy ground environment. All tooling and muds were supplied by Blick Industrial. Predominantly, an MI Swaco bentonite system was used for the drilling fluid, also due to the pure sand environment. The location system used was the DCI, Falcon F5 with IGPS module. This allowed the operator to achieve the greatest possible accuracy and a better as-built upload report for the client.
Due to the wet running sands on the project, UINZ looked to minimise the amount of down-hole agitation. This was achieved by drilling out the pilot bores over lengths of 100 to 150 m, depending on the presence of any conflicting services and undertaking a single-pass pull back of the 180 mm diameter PE pipeline, that was being installed as the product pipe, using a 250 mm diameter Turbo reamer to create and maintain the required bore diameter.
Where elsewhere on the project a 250 mm diameter PE pipeline was required as the installed product, UINZ undertook as single pre-ream to upsize the pilot bore using the 250 mm diameter reamer. The product pipe was then installed behind a 300 mm diameter Turbo reamer. For UINZ, this worked best in the challenging running, highly-saline sand conditions.
UINZ was able to handle the challenging ground conditions well having worked in the area previously. The location is a slender peninsula between a beach and an estuary, so previous local knowledge gave the contractor an ‘edge’ over competitors when it came to tendering and winning the work and ultimate delivery on the project.
In total over the complete project some 4,000 m of 180 mm diameter PE pipe and 400 m of 250 mm diameter PE potable water mains and 63 mm sub-mains for connections were installed. The 180 mm and 250 mm dimeter PE pipelines were supplied in 15 m lengths and all of the pipe welding was carried out by Polyweld NZ Ltd, which has a long-term association with UINZ. Polyweld utilised various welding systems to make up the project’s PE pipes including:
- EF – MSA 2.1 Eletrofusion Welders, with Blue Tooth capability and a welding range from 25 mm up to 1,000 mm diameter
- Butt welders:
> George Fischer CNC 315 mm, with Blue Tooth capability, welding in the range from 90 mm up to 315 mm diameter. This system also had GPS capability.
> George Fischer CNC 400 mm, with Blue Tooth capability, welding in the range from 125 mm up to 400 mm diameter, again with GPS capability.
This project commenced in April 2021 and finished in October 2021 although a couple of COVID lockdowns did not help project timings in any way.
UINZ not only has HDD in its contracting portfolio, which offers cost effective, faster, more sustainable installations and creates less disruption for stakeholders, but also Pipe Ramming which is often preferred for critical asset crossings such as State Highways, rail crossings and significant service crossings as no void is created as the required carrier pipe is installed; and Pipe Bursting for in-line renewal of laterals.