THE PROJECT
Owned by Rio Tinto Alcan and located 10 km north-west of Gladstone, the Yarwun alumina refinery produces more than 1.4 million tonnes of alumina a year. The caustic storage facility is a critical component of the refinery operation. The refinery uses the Bayer process to extract alumina from bauxite, which is subsequently used in the production of aluminium.
PSM was engaged to provide a detailed design for two storage tanks, each with a capacity of 58,000 tonnes to store a 50% solution of sodium hydroxide (caustic).
OPPORTUNITIES
The project was completed on poor ground conditions consisting of uncontrolled fill overlying soft marine clay and a site comprising a reclaimed peninsula that was previously tidal mudflats and mangroves.
Engineering and technical opportunities included:
- Differential settlement due to variable ground conditions
- Settlement-sensitive hydraulic structures
- Embankment stability and integrity of inlet structure, outlet pipe, leak detection system and HDPE liner
- High velocity flow at inlet with a potential to damage the HDPE liner.
APPROACH AND INNOVATION
Following rigorous assessment and modelling, PSM’s tailored approach included:
- Design of tanks to store 50% solution of sodium hydroxide (caustic) with engineered fill construction incorporating multiple geo-synthetic and clay liners
- Development of inlet and outlet structures and a leak detection system
- Extensive use of cone penetrometer testing (CPT) to delineate soft soil layers
- Completion of ground improvement works using pre-loading combined with settlement monitoring
- Physical modelling of inlet structure to verify suitability of the design to protect the HDPE lining
- Assessment of lining deformation due to settlement caused by both embankment and caustic loading.
OUTCOMES
PSM designed storage facilities with an engineered fill construction that incorporated multiple geo-synthetic and clay liners. The design of the storage facility included ground improvement works, inlet and outlet structures and a leak detection system.
The success of the storage facility led to PSM undertaking design of similar caustic storage tanks for Orica on a site next to the original structures.
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