Shore Approach and Shore Crossing Design – Pluto LNG Project

Background

Woodside Energy Ltd engaged Atteris in 2005 to design the shore approach and shore crossing for the Pluto Export Trunkline System, which comprises a 36-inch gas pipeline and a 4-inch MEG line.

Work Performed by Atteris

The early concept design considered several pipeline route options, and as the design progressed, a final route was selected in 2006, with a landfall at Holden Point on the Burrup Peninsula.

The shore approach design for the trunkline system included developing engineering solutions to deal with:

  • Rough seabeds with exposed limestone rock formations
  • Erodible calcareous seabed sections comprising silts and sands, including “glay soils”
  • Laying the Pluto Trunkline System close to the Pluto LNG Offloading Jetty under construction, two existing large diameter gas pipelines, a dredged material dumping ground
  • The crossing of the NWS shipping channel
  • A shoreline comprising igneous hard rock and a major heritage site.

The final design delivered by Atteris in 2008 was based on a conventional open-cut and cover solution for all area. The engineering work included detailed numerical analyses and physical model testing, in combination with cost, schedule and risk studies, and constructability assessments.

Interfacing was effectively and successfully undertaken by Atteris engineering staff with the Pluto Project onshore engineering team, Woodside’s environmental coordinators, Woodside’s survey group and Woodside’s Marine Group. Atteris also effectively managed a selective group of specialist sub-consultants to support the design engineering work.

Notable innovations included in the final design of the shore approach and shoreline crossing are:

  • A novel yet cost-effective solution to cross the NWS shipping channel
  • The use of locally sourced sand to backfill pre-dredged trenches for both hydrodynamic stability as well as for anchor drag protection, instead of quarry rock; this design was pioneered by Atteris on Woodside’s TSEP project in 2002, and improved on the Pluto Project
  • Significant optimisation of the trench depths by using sophisticated soil liquefaction analysis of trench backfill material, and scour studies.

Benefit

The shore approach and shore crossing design resulted in a very cost-effective solution from both a cost and schedule perspective, with manageable levels of risk and limited environmental impact.

The innovations contributed to the Pluto Project winning an Engineering Excellence Award by the Institution of Engineering WA in 2012.