Credit: University of Western Australia
Sediment on the seabed can behave in unexpected, peculiar ways. This makes the building of durable offshore platforms and pipelines for oil and gas extraction a major challenge. Coming up with engineering solutions to solve this problem is Dave White's job, as a geotechnical engineer based at the University of Western Australia (UWA) in Perth.
One of the weird phenomena that White and his group have investigated is the 'walking' of pipelines along the seabed like a caterpillar. Some movement is expected, but an excessive amount can damage the end connections of the pipeline. The researchers knew that as the pipelines are switched on and off, they expand and contract by a few microns each second.
What they didn’t realise, until looking more closely, was that these slow movements are enough for water pressure to build up between the pipe and the seabed. As the pipe slides along the seabed, it creates a cushion of fluid which lowers friction between the two surfaces. Consequently, the pipes are free to go a-wandering.
Anchoring pipes to the seafloor is one solution to the problem. "We are also working on general models which will help designers to assess what changes in water pressure are likely for a given pipeline and a given sediment type, allowing them to choose safe design values of seabed friction," said White.
White's research includes experimental work, numerical simulations and collection of data in the field, all of which are used to develop methods to predict the behaviour of seabed sediments and the structures that rest upon them.
His experimental techniques include spinning sediments from the seabed in the two large centrifuges at UWA. The centrifuges are larger versions of what you’d see on most lab benchtops, measuring 4 m and 1.2 m in diameter. The group are also about to take delivery of a government-funded 10 m diameter centrifuge, the largest in the Southern Hemisphere. The centrifuges simulate the high stresses that occur tens of metres beneath the bottom of the ocean. The experimental findings are then used to calibrate numerical models of sediment behaviour and the response of man-made structures that sit in the sediment.
White moved to UWA from the University of Cambridge in 2007, becoming UWA's youngest professor in the process. He has won several awards for his achievements; most recently he was named the 2011 Early Career Scientist of the Year at the Western Australia Science Awards. In moving to Australia, he has switched his attention from the seabed of the North Sea to the more challenging environments found off Australia's west coast.
As the oil and gas industry explore more demanding environments, White and his co-workers face new engineering challenges. "Planned developments offshore Western Australia are moving into deeper water, where the sediments are different, and new engineering challenges are emerging. I expect that the industry will throw up enough new problems that need new research to keep our group busy for the rest of my career."
