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Microtunnelling under Deebing Creek

Queensland Urban Utilites recently co-ordinated a site visit at the Deebing Creek Project in Ipswitch, Queensland, demonstrating the microtunnelling of a 500 m gravity sewer main with Rob Carr slurry microtunnelling machines.

Project proponent Queensland Urban Utilites (QUU) contracted Rob Carr for both the design and construction of the Deebing Creek Project. The project involves construction of a new trunk sewer main and a new pump station, which will prepare the Deebing Creek and Ripley Valley areas for additional supply demand created by population growth.

As part of the Deebing Creek catchment, the existing users in Booval, Silkstone, Eastern Heights and Raceview will gain additional capacity from the construction of the new trunk sewer main. The works will meet the flow capacities required by future population growth and the associated increased supply demand from the Deebing Creek and Ripley Valley areas.

The works are categorised as temporary, with a five-year design life. The construction has incorporated the need for future upgrades beyond this timeframe, including two manholes throughout the new trunk sewer main for ease of future connections.

The project is part of a record $A3.2 billion ten-year capital works investment from QUU to support growth and maintain water and sewerage services.

Major project components:

    Over 500 m of microtunnelling from DN400 to DN1,000

  • 60 m of open trench pipe installation
  • Construction of seven manholes from DN1,200 to DN3,000, four of which are HDPE lined
  • Construction of a new pump station inclusive of two concrete cast in-situ caissons of 3.2 m and 3.6 m to depths of 14 m and 16 m respectively
  • Associated diversions and live connections
  • Microtunnelling to reduce project costs

The original client concept design included a new pump station, eleven new manholes and 14 new pipelines totalling 676 m. When Rob Carr took responsibility for the project (including consultation, design, management and construction), the company amended the original designs for greater efficiency and resource use. Robb Carr’s designs provided the exact same functionality with only seven new manholes and eight new pipelines totalling 583 m, including the proposed pump station. This provided significant cost savings.

The project involves the construction by microtunnelling of two DN1,000 pipelines of over 180 m each, and the construction of a new pump station inclusive of two cast in-situ concrete caissons for the grit collector and wet well of the pump station, at 14 m and 16 m deep respectively.

The microtunnelling works include installation of DN400, DN600 and DN1,000 HOBAS pipe in varying ground conditions. Rob Carr utilised multiple machine types on these drives depending on the individual size and ground type to ensure successful construction of each individual line.

Project constraints ranged from:

  • Construction in a sensitive environmental area
  • Co-ordination and management of environmental controls
  • Co-ordination and management of community
  • Construction in wet silty and alluvial soils, as well as high strength rocks
  • High level of OHS&E management, planning and co-ordination
  • Decommissioning of existing infrastructure
  • Existing infrastructure and sewer diversions
  • Multiple bypassing, break-ins and connections to existing infrastructure
  • Land restrictions due to the project resting on a cultural heritage site for Indigenous Australians.

Rob Carr General Manager Angelo Soumboulidis said Rob Carr was able to provide a novel design solution to the land restrictions by extending individual pipeline lengths. This technique was able to provide the most cost efficient construction method for QUU.

Construction works are expected to be completed in October 2012, weather permitting.

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