Stevenson has helped to create a safer and more aesthetically pleasing coastline on Auckland’s North Shore. The project, for the North Shore City Council, involved repairs to the 1960′s built sewer line, which runs from Murray’s Bay to Takapuna.

Over the years weathering degraded the pipeline and support systems that sit along the shoreline beneath the sandstone cliffs. To protect the pipeline the North Shore City council decided to encase it in concrete. It was also decided to shape and colour the concrete casing, blending it into the surrounding cliffs and rock formations; improving the overall visual appearance of the coastline. The new concrete structure helps to slow and reduce the power of the waves, as well as allow sand to build up on the beach.

Construction involved several detailed stages. First the existing pipe was water blasted clean, and then a sandstone trench was cut as a key about 700mm deep and 300mm wide. This was followed by placement of concrete fill over the pipes. The first layer contains Microsilica 600. The structural integrity is provided by the application of the steel fibre concrete. The final stage involves spraying and shaping the decorative coloured concrete topcoat. This concrete contains Microsilica 600, oxide and superplasticiser.

Partners

  • The main contractor for the project was Gideon Contractors.
  • Natural Pools and Rocks were subcontracted to carry out the concrete spraying and texturing.
  • All concrete was supplied by Stevenson Concrete.
  • The oxide was specially designed for the job by Oxide Distributors and the steel fibre (Dramix) specified and supplied by BOSFA.

A collaborative approach was applied to the project, with a lot of work going into the design of different types of concrete. All the mixes contained different and specialty admixtures. Delivery of the concrete created its own challenges. The job could only be accessed between tides across a sand beach (with trucks that weigh 22 tonnes laden). Once laid there also had to be enough time for the concrete to gain strength so that it was not damaged by the wave action on the high tide.

Meeting environmental challenges were critical to the project’s success. No excavation or construction debris could be left on the foreshore so good working practices were essential at all times. The repairs to date have proved successful and the concrete looks very similar to the surrounding cliffs. Another positive aspect is that local marine life has already started to attach itself to the concrete.