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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.
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.
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.
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New Zealand is the antipode of Spain, so it is diametrically opposite on the globe. A trip by plane from Austria therefore takes about 24 hours. Mr. Georg Offenthaler is also responsible for New Zealand in the sales department and paid a personal visit to our representative AGRU New Zealand as well as to the most important end customers and their projects.
The largest AGRU concrete protection liners project ever, the "Auckland Central Interceptor" wastewater tunnel project, was of course also on the visit schedule. Together with the project manager responsible for the project at AGRU NZ, Nathan Croucher, Mr. Offenthaler visited the superlative project. After an extensive safety training including a backpack with survival techniques, the construction site elevator took them 80 m down into the depths. The Central Interceptor Tunnel has a diameter of 4.5 meters and runs over a length of 14.7 kilometers from the center of Auckland to the sewage treatment plant in Mängere. AGRU is supplying Ultra Grip concrete protection liners in 3 mm thickness and four different colors to protect the tunnel structure from corrosion. These are cut to size in Auckland and cast into so-called tubbings. A segment is a prefabricated concrete segment including a concrete protection liners for stiffening in tunnel construction. In modern tunnel construction, the segments are laid by the tunnel boring machine, which also supports itself in the axial direction to reach the edges of the segments already laid.
The tunnel in Auckland will be lined with a total of 52,000 segments by 2026. Six segments each will form a complete ring. Georg Offenthaler also visited the Wilson company, which pre-produces the segments and delivers them to the construction site. Very high demands are placed on a segment in terms of accuracy of fit. The error tolerance is normally in the range of one to a few millimeters. Casting is therefore carried out in metal molds. To allow changes of direction, the concrete segments are designed and manufactured slightly beveled so that they are a few centimeters wider on one side. When paving straight sections, the segments are installed alternately, each offset by 180°; for curves, this offset is interrupted. In this way, segment rings can be produced evenly in series. So far, the construction site is proceeding according to plan. The first construction phase is scheduled for completion at the end of 2023. However, AGRU will continue to supply Ultra Grip concrete protection liners until the end of the project in 2026 via AGRU New Zealand, which was founded by Rainer Grün in 2002.