Geotechnical advice, Darwin East Arm Wharf, Northern Territory, Australia

Opened in 2000, the East Arm Wharf is a 750 m long facility located in Darwin Port. The largest facility on Australia’s north coast, the facility is capable of accepting vessels up to 80,000 tonnes, with a maximum draft of 15 m. The Wharf comprises a bulk liquid berth, a common user facility, a container facility and a bulk loading berth. The container berth is served by a rail-mounted container crane with a heavy lifting capacity of 70 tonnes at 10 m outreach.

PSM was engaged to provide specialist advice on several complex geotechnical issues associated with wharf construction.

A huge tidal range of 7.8 m has resulted in a very high wharf face. Construction of the wharf structure on existing bund built from materials under water, makes it susceptible to deformation.

Other engineering and technical opportunities included:

• A range of in-situ material requiring detailed investigation and analyses
• Fill materials to backfill the wharf being limited to weathered rock requiring particular attention
• Assessment of the phyllite bedrock critical to the capacity of the structure.

PSM’s tailored approach included:

• Assessment of the lateral load capacity of the weathered phyllite bedrock into which the sheet piles were driven
• Assessment of deformation of the wharf structure and the effects on tension anchors
• Monitoring of completed wharf
• Provision of advice for Stage 2 regarding construction methodology for the backfilled wharf
• Development of a comprehensive geological and geotechnical model
• Analysis of interaction with sheet piles to assess risk to design from various potential failure mechanisms
• Inclusion in the design of structural pins at the base of sheet piles to improve strength
• Regular monitoring reviews to ensure appropriate performance.

PSM’s involvement enabled resolution of key technical challenges and completion of structure without incident. As a result of ongoing monitoring the client is able to manage risks relating to time-dependent deformation of the geotechnical materials used in the wharf’s construction.

Services: #Geological #Geotechnical #Phyllite bedrock