HDD, Tunnelling

HDD under Maroochy River

The pipeline beneath the river, installed by Unitywater using horizontal directional drilling (HDD), marks the first stage of a three stage project that will see the closure of the Suncoast Sewage Treatment Plant (STP) and the transfer of the sewage to the Maroochydore STP, which has the capacity to fully treat it.

The $A11 million project will also incorporate a 6 km, 560 mm diameter pipeline and a new transfer pumping station to connect the existing sewage network north of the river to the Maroochydore STP via the sub-river pipeline.

Because traditional excavation and trenching was not possible under the Maroochy River, Unitywater used HDD with a Prime PD 500 rig to install the pipeline, avoiding any unnecessary environmental impact and minimising surface disruption.

Following two years of planning, the utility appointed Coe Drilling in February 2013 to conduct HDD of the transfer pipeline. Construction commenced in July and the pipe was pulled under the Maroochy River in early September 2013.

Unitywater Executive Manager, Infrastructure Planning and Capital Delivery Simon Taylor said “We are pleased with the success of the drilling operation. The route was a complex one and required the rig to drill horizontal and vertical bends as it made its way under the river.”

A Coe Drilling spokesperson told Trenchless Australasia “Given the pilot hole alignment and geological conditions the Maroochy River crossing was a very technically challenging project. The initial concerns regarding the risk of hydrofracture and potential project failure or re-design were alleviated by careful and rigorous project planning, design and management of these design parameters on-site by the experienced drill crew; this all accumulated in a successfully delivered project. Coe Drilling Pty Ltd are pleased of their involvement with Unity Water and our ability to work together to deliver such a successful project”.

The Suncoast STP will be decommissioned after the completion, testing and commissioning phases of the new sewerage rising main and new sewage pumping station in the second half of 2014.

This project is part of the $A680 million capital works program Unitywater is rolling out over the next five years to increase the network capacity and cater for future population growth in the Sunshine Coast and Moreton Bay regions.

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