The process and benefits of direct pipe for the Army Bay ocean outfall (NZ)

Abstract

In 2017, the Army Bay Ocean Outfall was a standout project for New Zealand. Technically complex, it pushed the boundaries of what is possible with the Direct Pipe® method and set a record for the longest Direct Pipe® installation at just under 2 km of DN1200 steelpipe, in a single drive. Watercare’s planning for the project started with early contractor engagement in 2013 to explore methods and alignments, to confirm constructability and optimise the design.. McConnell Dowell went on to successfully tender a Design & Construct solution in a competitive tender process in 2016, based on Herrencknechts Direct Pipe® technique. A technique previously used by McConnell Dowell in Thailand to successfully completed four Direct Pipe installations. At tender time, this technology had not been used in Australia or New Zealand. It was developed by Herrenknecht in the early 2000’s and used for the first time in 2007 to install 464 m of steel pipe under the Rhine near Worms, Germany. It combines the advantages of Microtunnelling and Horizontal Directional Drilling (HDD) to install steel pipe from DN600 to DN1500 in a single, continuous operation. A particular advantage is that all the work is carried out from one side, making it ideally suited to ocean outfall projects like Army Bay. This paper discusses the technique and how it was used to address the client and contractor’s concerns on a difficult and challenging project.

Techniques