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Somersby Road collapse, Somersby, NSW, Australia

THe project

The Old Pacific Highway at Somersby collapsed during a major storm on 8 June 2007. The collapse occurred where culverts conveyed Piles Creek beneath the road embankment. Two adults and three children drowned when their car drove into the void created by the collapsed road.

PSM was engaged as the Road Transport Authority’s (RTA) technical expert for the Coronial Inquest.

engineering and technical opportunities

Identifying the cause of failure, after the collapsed structure had been washed away, presented a key challenge. There was also little factual data from the maintenance and inspection regime and an unusual failure mechanism which had previously been undocumented. The project presented an opportunity for multi-team collaboration.

Approach and innovation

PSM’s tailored approach included:

  • Rigorous assessment of the structure, maintenance records and eye witness accounts
  • Systematic and thorough inspection, testing and documentation of structure during deconstruction
  • Research of the literature on corrosion mechanisms
  • Inspection and evaluation of like structures to benchmark the inferred failure mechanism
  • Investigation and deconstruction of similar structures
  • Testing to assess in-situ material properties
  • Extensive liaison with interdisciplinary experts (e.g. corrosion and hydrology).


Technical findings submitted by PSM showed that the structure (culvert) had been satisfactorily built and maintained. The inquest found that the RTA was not responsible for the collapse. The technical evidence heightened understanding of the failure mechanism and informed future management of similar assets.

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