GLNG Narrows Crossing Design

Benefits

GLNG utilised specialist expertise from Atteris to successfully and cost-effectively deliver a major waterway crossing for a 42-inch gas transmission pipeline. This project has set a benchmark for the industry, with the same engineering concept now being used gobally for major waterway crossings in onshore pipeline routes.

Background

GLNG incorporates the development of CSG resources in the Surat and Bowen Basins in south-east Queensland, a 420 kilometre underground gas transmission pipeline and a two-train liquefaction and storage facility on Curtis Island, Gladstone, Queensland.

When planning the pipeline, GLNG faced a very challenging waterway crossing named “The Narrows”, between mainland Australia and Curtis Island.

Work Performed by Atteris

GLNG engaged Atteris to undertake FEED and support the Detail Design and Construction phases for the Narrows Crossing. The selected concept for the crossing involved a 4.4 km long, 3.4 m diameter segmental lined concrete tunnel to serve as a conduit for the 42 inch diameter pipeline and accompanying fibre optic cable (FOC).

Atteris performed the following work on this project:

  • Concept development of the waterway and mudflat crossing, by assessing crossing concepts including open cut and cover, horizontal directional drilling and tunnelling; tunnelling was selected as the most cost-effective option for this crossing
  • FEED of the 4.4 km long and 3.4 m diameter concrete tunnel and 42-inch diameter gas transmission pipeline through the tunnel, including addressing complex engineering aspects such as
    • pipeline material corrosion protection (including CP design)
    • flooded, grouted or air-filled tunnel
    • design of tie-ins to overland pipeline
    • pipeline installation concept development
  • Detail design, including CP system, tie-in spools; and provision of owners engineering to the GLNG team for construction engineering and on-site construction supervision
  • The spool design was optimised to ensure adequate allowance was made for the spool to flex under expansion, pressure and thermal loading, while taking into account the uncertainties related to the foundation stiffness, and minimising the spool footprint required.