Three Trenchless Techniques Provide Solutions for the New Lynn Branch Sewer

The trunk sewer capital works programme for the New Lynn catchments in West Auckland has successfully improved the environment. The wastewater upgrades eliminated a number of wet weather overflows and also allowed provisions for future population growth. 

The project involved the diversion of the existing West Lynn Branch Sewer and construction of a new South Lynn Branch Sewer. The West Lynn Diversion Sewer is a 600/1050 gravity pipeline laid predominately along road reserve at depths ranging from 3 to 12 metres. The South Lynn Branch Sewer was replaced with a new 375/300 gravity pipeline positioned deeper to allow for removal of pipebridges. A short section of 250mm network sewer was also constructed, relieving the existing under capacity pipeline. 

The new pipelines were all installed utilising a combination of directional drilling, mircotunnelling of PE pipes, and pipe jacking methodology. Technical challenges of the project included the depth of the pipelines and associated manholes, installing the pipelines at shallow grades, working within numerous private properties and conquering the variable ground conditions. The first stage and first contract of the project along Clark St was successfully coordinated with the New Lynn Train Station and roads upgrade contracts. The South Lynn catchment upgrades were delivered in two contracts and were completed in late 2013. 

This paper outlines the technical challenges and how the solutions the team developed met those challenges.