AGRU concrete protection for giant wastewater tunnel

The Auckland Central Interceptor is the largest wastewater project in New Zealand's history. This super-sized wastewater tunnel will transport sewage from the west of the city to the Māngere Wastewater Treatment Plant in the east. Commissioned by Watercare Services Ltd, the new wastewater tunnel will cost around NZD 1.2 billion and is scheduled for completion by 2026. AGRU Kunststofftechnik supplies concrete protective liners made from polyethylene that will protect the wastewater tunnel against concrete corrosion in the long term.

The access shaft is protected from concrete corrosion with green Ultra Grip concrete protective liners. [Source: Watercare]
The access shaft is protected from concrete corrosion with green Ultra Grip concrete protective liners.

The Central Interceptor Tunnel is 4.5 meters in diameter and will run for 14.7 kilometres from Grey Lynn under central Auckland and Manukau Harbour to Māngere. The tunnel is situated between 15 and 110 meters below the surface. Together with two smaller connecting tunnels, the main tunnel will collect wastewater from the existing network and convey it to the Māngere Wastewater Treatment Plant. For maximum durability of the multi-billion infrastructure project, Watercare Services Ltd has chosen AGRU concrete protective liners.

HD-PE lining protects against concrete corrosion

The high-quality lining made of high-density polyethylene effectively prevents concrete corrosion and abrasion. Thanks to their 13 mm long anchor studs, AGRU Ultra Grip concrete protective liners have enormously high pullout force. The thermoplastic lining protects the concrete against corrosive gases generated by the wastewater in the tunnel. This allows for maximum service life of the tunnel structure. For easier sewer inspection and detection of damage, the tunnel is divided into four different coloured sections. AGRU supplies the Ultra Grip concrete protective liners in 3 mm thickness. While the access shafts are lined in green, the sewer tunnel is lined in yellow, pink, blue, grey and sealed by extrusion welding.

AGRU supplies Ultra Grip concrete protective liners for the largest wastewater project in New Zealand's history.  [Source: Watercare]
AGRU supplies Ultra Grip concrete protective liners for the largest wastewater project in New Zealand's history.
Assembly of the TBM and start of tunnelling work at the Mangere pump station. [Source: Watercare]
[Source: Watercare]

This project is not only intended to accommodate the population growth in this major city of 1.7 million inhabitants and the resulting increased demand for wastewater. In older parts of downtown Auckland, wastewater and storm water flow into a combined pipe network. During heavy rains, storm water can flood these pipes. Currently, during heavy rains, storm water contaminated by fecal matter is discharged into Waitematā Harbour. The new wastewater tunnel is expected to significantly reduce these overflows.

The construction contract was signed with the Ghella Abergeldie Joint Venture in March 2019. A 200 m long Herrenknecht tunnel-boring machine is in use. The finished wastewater tunnel will have a gradient of 1:1000 to allow wastewater to drain to Māngere. A total of sixteen access shafts with a depth of up to 65 meters will be built for maintenance and operation. In the course of this, control and overflow structures as well as air treatment facilities will also be built for future operation.

Prior to construction of the project, AGRU Kunststofftechnik GmbH and Agru New Zealand Ltd provided technical support for the installation of the lining for the shafts and tunnel. Agru New Zealand Ltd provided on-site extrusion welding support and training to the site crew. AGRU Kunststofftechnik GmbH and Agru New Zealand Ltd. have coordinated and continue to coordinate the supply of approximately 210,000 m² of lining for the project.

Construction of main tunnel is lined with yellow, blue, pink and grey Ultra Grip concrete protective liner.  [Source: Watercare]
Construction of main tunnel is lined with yellow, blue, pink and grey Ultra Grip concrete protective liner.
In this section of the tunnel, blue liner is used. [Source: Watercare]
[Source: Watercare]

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