Customer: Watercare Services Limited

Contract: Design & Construct

Location: Warkworth, New Zealand

 

 

 

 

Project Capabilities

Pipelines Tunnelling & Underground

 Fast Facts

  • 4.3 km of 630 mm diameter pipeline from Snells Algies to South of Martins Bay
  • A 2.2 km of 1.2 diameter pipe installed using the Direct Pipe system
  • A 230 m marine dig and lay section.
  • Two southern approach spans are 12m wide creating dedicated fishing bays
  • The northern and southern abutments consist of 1.2m wide reinforced concrete blade walls
  • The new bridge provides up to eight meters clearance for vessels during low tide, to increase access to the upper harbour
  • The replacement bridge will be a shared public space with a gentle slope to provide easy access for many users

 

Scope:

Upgrading the wastewater network in Mahurangi East to cater for rapid growth 

The Snells Algies wastewater pipe and outfall construction project is the first phase of a three stage scheme to supply the Warkworth and Mahurangi East communities with reliable wastewater services to cater for population growth. The scheme will improve water quality in the Mahurangi Harbour and deliver an upgraded wastewater system.  

McConnell Dowell were awarded the design and construct contract by Watercare in March 2019. It continues to build on McConnell Dowell’s extensive track record in the construction of major marine outfall pipelines in New Zealand.

The Challenge

The project involves the following elements:  

  • Constructing 4.3 kilometres of 630mm diameter HDPE pressure/gravity main by open trench methods following the public road alignment. 
  • Installing 2.02 kilometres of 1.2 diameter steel pipe using the Herrenknecht Direct Pipe® system under private farmland out to the marine recovery trench 550mts off the coast. 
  • Laying a 230m outfall pipeline on the seabed for disposal of high-quality treated effluent into the Hauraki Channel. 

The Solution

Our solution features the use of the Herrenknecht Direct Pipe® system with single 750t thruster unit to install a similar length of trenchless pipeline to that completed in 2019 as part of the Army Bay outfall project, where we successfully achieved a world record for the longest Direct Pipe installation of 1930m. 

The star of the show is a Herrenknecht AVN1000 Micro Tunnel Boring Machine (MTBM) named Piper by students from a local primary school. The 1220mm OD steel pipe for the Direct Pipe was procured from Shanghai, it has 32mm wall thickness and each length is 11.8m weighing 1 tonne per meter. 

To overcome the challenge of moving and handling the heavy pipes on site, a number of pipe lifting and aligning frames were designed and fabricated. 

The launch pit for the Direct Pipe MTBM features a ground retaining system to support the trench excavation and high strength vertical anchors for the Direct Pipe thruster. Piper was launched through a launch eye seal which stops any of the annulus lubrication fluids or groundwater entering the excavation. 

The Key to Success:

The Transport Agency has maintained a strong community focus from the early engagement and consultation through to the construction phase.

Maintaining the connectivity and accessibility around the old bridge while work is underway is important because there are two popular community assets on either side of the harbour next to the construction sites. There is the walking and cycling path on the northern side, and the causeway to the boat ramp and Waterfront Reserve on the southern side.

We developed the traffic management plan in consultation with local board members, cycle advocacy group Bike Auckland and the harbourmaster to ensure that we maintained safe access around the construction sites.

Space was limited so we minimised risk by creating separate areas for construction traffic and the public.

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