Concrete protection for superior wastewater tunnel

The Auckland Central Interceptor is the largest wastewater project in New Zealand history. This massive sewage tunnel will transport wastewater from the west of the city to the Māngere wastewater treatment plant in the east. The new sewage tunnel, commissioned by Watercare Services Ltd, will cost about NZD 1.2 billion and should be completed by 2026. AGRU Kunststofftechnik is supplying concrete protection plates for a polyethylene lining system to provide long-term protection for the wastewater tunnel against concrete corrosion.

The Central Interceptor Tunnel has a diameter of 4.5 meters and a length of 14.7 kilometers and runs from Grey Lynn under downtown Auckland and Manukau Harbour to Māngere. The tunnel will be between 15 and 110 meters below the surface. Along with two smaller connecting tunnels, the main tunnel will collect wastewater from the existing network and transport it to the Māngere wastewater treatment plant. For maximum sustainability of the multi-billion infrastructure project, Watercare Services Ltd is having the wastewater tunnel lined with AGRU concrete protection panels. 

PE-HD cladding protects against concrete corrosion

The high-quality high-density polyethylene lining effectively prevents concrete corrosion and wear. Thanks to the 13 millimeter long anchor bolts, the AGRU Ultra Grip concrete protection panels have an enormously high pull-out force. The thermoplastic lining protects the concrete from corrosion due to the gases generated by wastewater in the tunnel. This enables maximum service life of the tunnel structure. To facilitate sewer inspection and damage detection, the tunnel is divided into four differently colored sections. AGRU supplies the Ultra Grip concrete protection plate in 3 mm thickness. While the access shafts are clad in green, the sewer tunnel is clad in yellow, pink, blue and gray, and sealed by extrusion welding. 

This project is not just to accommodate population growth in the large city of 1.7 million and the resulting increased demand for wastewater. In older parts of downtown Auckland, sewage and stormwater flow into a combined pipe system. During heavy rainfall, stormwater can overflow these pipes. Currently, rainwater contaminated with fecal matter is discharged into Waitematā Harbor during heavy rainfall. The new sewage tunnel is expected to significantly reduce these overflows.

The construction contract was signed in March 2019 with the Ghella Abergeldie Joint Venture. A 200-meter Herrenknecht tunnel boring machine will also be used. The finished wastewater tunnel will have a slope of 1:1000, allowing wastewater to drain to Māngere. For maintenance and operation, a total of 16 access shafts with a depth of up to 65 meters will be built. As part of this, control and overflow structures and air purification facilities will also be built for future operation. 

Leading up to the project, AGRU Kunststofftechnik GmbH and Agru New Zea-land Ltd provided technical support for the installation of the shaft and tunnel lining. Agru New Zealand Ltd provided on-site support and training for the extrusion welding personnel. AGRU Kunststofftechnik GmbH and Agru New Zealand Ltd coordinated and continue to coordinate the supply of approximately 210,000 m² of cladding for the project.