A new approach to the old problem of laying pipelines in soft soil has become a feature of the $8.2 million project to build a sewer main from Judea to Memorial Park.
Instead of building heavy walls and structures to support the weight of a pipeline in boggy soils, a piling rig is being used to inject soil-strengthening slurry into the ground.
Tauranga City Council project manager Richard Myers said the strengthening would make the ground strong enough to help maintain the line and level of the pipeline.
The council chose the construction method in a design-and-build tender process for the link which will form part of the $102 million southern pipeline project from Maleme St.
The 1.2km pipeline linking the Judea and Memorial Park pump stations was a cheaper and more flexible back-up than building huge storage tanks needed if the sewage disposal systems failed. "It offers more protection at least cost," project manager Richard Myers said.
An estimated 500m to 600m of the route will need the special soil treatment up to the point where the pipeline left Graham Park and went under Te Papa Peninsula, and from where it emerged at Memorial Park.
Mr Myers said the soil stabilising would happen quickly although the total Downers contract would take more than 12 months, including drilling the pipeline through the peninsula on a line with 10th Ave.
The southern pipeline was principally to take the sewage from the city's growing southern suburbs and re-route it to the Te Maunga treatment works. Otherwise the Chapel St treatment works would become hopelessly overloaded. The Chapel St system was already failing in heavy rain.