Fulton Hogan Manawatu, as main contractor for Rangitikei District Council in New Zealand required the installation of some 8,000 m of 315 mm diameter PE wastewater pipeline between Bulls to Marton in the Manawatu area. Rangitikei lays roughly south-central on New Zealand’s North Island. The consulting engineer for the project was GHD.
The main route of the wastewater connection pipeline ran alongside a State Highway, so the methodology selected for the installation works had to minimise the need for traffic management and where ever possible reduce interference for the public.
This led to the selection of horizontal directional drilling as the preferred option, particularly as the ground conditions along the route proved ideal for technology, these being silty and sandy clays.
After a careful selection process, the project was awarded to Utilities Infrastructure New Zealand (UINZ). HDD also offered increased productivity when compared with traditional trenched installation techniques. UINZ required several visits to the site as part of its own ground investigations and ultimately selected its Vermeer Navigator 6090 with a Falcon F5, IGPS and DCI Aurora guidance set-up on board for the project. Given the sandy clays in this area UINZ also decided to utilise an MI Swaco Max bore Bentonite and a small amount of MI Swaco, Polyplus RD and Platinum DD additives as the drilling fluid to provide more efficient bore cleaning. All down-hole tooling was from specialist tools manufacturer Melfred Borzall, and this instance the contractor used a Tornado reamer for pilot hole expansion.
After completing each pilot bore, the sandy clays and the diameter of the pipe at 315 mm required UINZ to undertake a pre-ream for each bore path prior to pulling in the final product pipe. Pilot boring was undertaken at the various project locations at between 300 and 350 m long with the excavation of an intermediate hole between the HDD entry and exit points. This method enabled UINZ to pre-ream each pilot hole over lengths of between 150 and 175 m at a time, pushing the reamer back out to the reception hole and then attaching and pulling in the product pipe on the second run through this time using a 450 mm diameter Melfred Borzall Tornado reamer.
Due to the stable nature of the clays in the bore, UINZ was able to pre-ream and pull back the product pipe without having to step up in reamer size. This sped up the operation considerably as no swapping out of reamers between pre-ream and pull back was necessary.
The PE pipeline being installed totalled some 8,000 m of 315 mm diameter wastewater pipeline with pipe welding being carried out by Polyweld NZ Ltd. Electro fusion welds were completed using MSA 2.1 Electro fusion Welders, with blue tooth capability and a welding range 25 mm up to 1,000 mm diameter. For Butt welding requirements two George Fischer systems were used: the George Fischer CNC 315 mm with blue tooth and GPS capability and a welding range from 90 mm up to 315mm diameter, and a George Fischer CNC 400 mm with blue tooth and GPS capability and a welding range from 125 mm up to 400 mm diameter.
Work on the project commenced on 9 January 2022 and is due to be completed in June 2022. Utilities Infrastructure New Zealand Ltd has the capacity to deliver a range of PE products for HDD and steel casing for pipe rams.