City Rail Link – Mt Eden Major Wastewater Diversion

Abstract

The Auckland City Rail Link Project is New Zealand’s largest civil infrastructure project to date. Design and construction of this project is being carried out by the Link Alliance. The project will provide two new underground rail stations in Auckland’s central business district, and a major expansion of the existing surface rail station in Mt Eden. In order to allow for construction of the rail tunnels and stations, extensive networks of utilities including potable water, wastewater, storm water, power, gas, and communications in and around the three station sites must be removed, protected, replaced or diverted. A major diversion is required for the wastewater conveyance at Mt Eden, where the new City Rail Link tunnels connect with the existing rail system. The design for this diversion comprises a DN560 SDR7.4 PE horizontal directional drilled installation, 450 m long, at depths up to 27 m below ground level with open excavation sections at each end. The design of this diversion includes many innovative aspects to meet the unique challenges of a large diameter horizontal directional drilled installation in the congested urban environment at Mt Eden and Auckland’s unique volcanic geology. The paper and presentation will describe several of these innovations, including firstly the approach to the investigations and design, and then to share observations on the advantages of the alliance mechanism for the delivery of complex underground infrastructure projects, and lessons learned.