Griffith Uni’s Dong-Sheng Jeng keeps ocean structures safe

From the moment pipelines began snaking their way between continents under the ocean and oil companies punched pylons through seabeds and topped them with giant platforms, engineers such as Dong-Sheng Jeng have had their work cut out for them.

The professor in Griffith University’s school of engineering and built environment is part of the worldwide effort to protect submarine structures, including infrastructure such as power transmission cables, that are subject to natural marine geo-hazards such as earthquakes, seabed movement, wind and wave loadings.

Apparently the challenge is simple. “Nowadays, the structure above the water can withstand environmental loading with current civil engineering technique, but without that stability in the seabed, they can fall down,” says Jeng, who is named as Australia’s top researcher in ocean and marine engineering in The Australian’s 2021 Research magazine.

However, the answers are complex, and Jeng’s research in the field has taken him into directions that include studies of porous flow, offshore geotechnics, ocean and coastal engineering, groundwater and offshore wind energy.

Geopolitical tensions are part of the reason many countries are funding this area of research, especially when it comes to the North Sea and the South China Sea.

“Whichever country can control the ocean resources will become the top country,” he says.

“Many countries are trying to do that in South China Sea recently. My research team don’t get involved in political issues, we just try to find a way to protect our marine environment.”

Controlling the resources means establishing and protecting reliable infrastructure – and vigilant maintenance. “The foundations can cause problems for the whole structure over time.Earthquakes are one main concern that can cause structural and foundational damage, but another is ocean wave loading. Waves generate pressure and that causes problems.”

How long it takes for the stability to erode varies greatly, but “wave loading just keeps going, it depends on the seabed condition and also on the size of the wave,” he says.

“If there is a storm – say a cyclone – huge waves generate wave pressure on the seabed and the foundations can develop problems immediately. However, if there are small waves, sometimes it takes years because they change the soil condition gradually.”

Water depth is also an issue. “In shallow water the waves will dominate a system; in deep water – over 100m – surface waves may not be a problem, although even steady wave pressure can create huge pressure beneath. In deep water, currents will be more important than wave pressure.”

Engineers like him design foundations taking into account the possibility of “20 year” storms with additional safety factors. “But there are still the unknowns, that’s why we are still doing research,” he says.

A recent project he is involved with is the Blue Economy Cooperative Research Centre’s 10-year effort to increase seafood and renewable energy production, specifically through the offshore technology program led by the University of Queensland’s Chien Ming Wang. “I am working on the mooring system and the anchors and associated foundation problems for the offshore aquaculture pens,” he says.

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