Drilling success on the Replacement Flows Project

Contracted by McConnell Dowell over a period of 13 months from November 2008 to December 2009, UEA installed high-density polyethylene (HDPE) mains in varying pipe diameters including 355 mm, 400 mm and 560 mm.

The Replacement Flows Project is part of the Western Sydney Recycled Water Initiative that consists of a joint venture between McConnell Dowell, United Group Infrastructure and General Electric (Deerubbin Water Futures), with Sydney Water as the principal client. The concept of the Replacement Flows Project is to transport tertiary-treated effluent from the existing sewage treatment plants at Quakers Hill, St Marys and Penrith, for further treatment in an advanced water treatment plant (AWTP). The AWTP will produce highly treated recycled water to be discharged into the Hawkesbury-Nepean River to replace flows of drinking water from the Warragamba Dam. The St Marys plant will produce up to 18 billion litres of recycled water a year.

The project’s objective is to save drinking water in the Warragamba Dam while maintaining the health of the Hawkesbury-Nepean River. Concentrate from the reverse osmosis process of the AWTP will be discharged to the Northern Suburbs Ocean Outfall Sewer at Dundas. The wastewater will then be treated at Sydney Water’s sewage treatment plant at North Head. To complete the upgrade, 55 km of pipeline was installed and divided into five different operating lines.

Although provided with initial designs and required invert levels to meet trenched sections, UEA was responsible for generating suitable bore designs not only to complete each crossing, but to maintain required grades, alignments, tolerances and depth of cover. The design aspect of the project enabled UEA to provide solutions that reduced restoration, minimised impacts to sensitive Cumberland Plain Woodland, and avoided trenching through areas of indigenous significance.

Trenchless technology in the works

UEA operates and maintains a fleet of Vermeer horizontal directional drilling (HDD) rigs. UEA’s assortment of drilling rigs utilised on the project included D36x50, D50x100, D100x120 and D300x500, ranging from 18 tonne to 136 tonne in pull back capability.

Working closely with McConnell Dowell and Sydney Water, UEA constructed the majority of trenchless crossings on the Replacement Flows Project via HDD.

Due to exacting grades, difficult access, busy arterial roads and requirements of pinpoint accuracy, the use of Paratrack HDD guidance technology was required on four crossings. The use of the Paratrack 2 system with Beacon Tracking enabled successful boring underneath the new M7 motorway, the intersection of Old Windsor Road and Powers Road, Prospect Highway from Seven Hills train station to Powers Road, and a crossing of James Ruse Drive exiting parallel to the Caltex multi-products pipeline.

The M7 Motorway crossing

One of the fundamental achievements of the project was the installation of the parallel dual lines under the M7 Motorway. Challenges of the project included setting up the D300x500 drilling rig within the Cumberland Plain Woodland, access into the parklands, exacting grades and limited pipe stringing options.

Pilot boring began from the M7 construction compound at a constant positive grade of 2.245 per cent, rising to 10.017 per cent. Once the pilot bore was completed, reaming was completed for the 560 mm before remobilising the drill rig to pull pipe. The process was repeated for the 355 mm bore line with pipe again installed after relocating the drill rig. After successful pressure testing of the bore, connections were made to the trenched pipeline

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