Central Interceptor Twin Rising Main

Mangere Auckland


Seipp has been working with Ghella Abergeldie on this large pipeline project. Works begun in March 2020 and are ongoing.
The scope of works consisted of:

  • Installation of DN1400 PE Twin Rising Main Pipeline, approximately 600m, including multiple raft foundation designs.
  • PE butt welding of pipe strings. String lengths between 40m and 240m long.
  • In-trench welds, using DN1400 PE butt welding machine
  • Temporary works, sheet piling, and trench shields to combat varying ground conditions and enable in-trench welding.
  • Dewatering and treatment of high groundwater
  • GRP cover installation
  • Internal double bladder pressure testing
  • 700m Haul Road construction
  • Installation of 350m of Ø600 – Ø450mm RCRRJ Stormwater, including a Ø2500mm x 4m Stormwater treatment device and varying size Manholes


The project involved the construction of a new DN1400 PE twin rising main, connecting the new Mangere Pump Station to the Mangere Wastewater Treatment Plant (WWTP) Confluence Chamber, as a part of the GAJV Central Interceptor Project.

The pipeline also passes over an operational open effluent channel and dives below two Earth Filter beds into the confluence chamber. At its deepest, the pipe invert is 5m below ground level. This is a continuous 600m Ø1400mm PE twin rising main. We were able to remove all flange connections and replace with an intrench butt weld.

Prefabricated straights, swan necks, bends, stub flanges and 450mm ‘Tee’ sections were manufactured offsite. These sections were later welded onsite to form larger continuous strings. These strings were installed into the trench, and welded intrench. Avoiding the need for flange connections.

In addition to the main contract works, we were also instructed to build a 700m Haul Road for the Central Interceptor TBM spoil cartage. Along side this there was also a 350m Stormwater line, kerb and Stormwater treatment device built and installed.

Twin Rising Main