Mathematical model for construction in erosion-prone areas

Designs for constructing buildings in erosion-prone areas may be simplified for engineers and technicians with a new mathematical model that can be used on a tablet.

Wei-Dong Guo, Associate Professor from the University of Wollongong’s Faculty of Engineering and Information Sciences (EIS), has spent three years trying to understand how to design foundation piles that resist soil movement in even extreme situations such as earthquakes and tsunamis.

On ground where there is the threat of erosion or the surface soil is soft, engineers may use piles, steel or concrete shafts to provide a firm support to build on. This technique is often used on coastal buildings or bridges and offshore structures that are built with foundations under water.

“At present, an engineer will apply a different theory to come up with solutions for each job, but my new model and solutions can readily resolve all problems for piles using the same parameters,” Guo said.

Using the model, a builder can choose basic parameters based on information contained in a geological report to calculate the depth, size and spacing of the piles needed.

“I envisage that one day, anyone can do the complicated design by using a portable iPad and keying a few parameters and pressing enter,” said Guo.

“A technician can do it. It will save large amounts of money and time on otherwise costly engineering design.”

The model can be used in the design phase or on existing buildings to provide a prediction about the structure’s safety against erosion and slipping soil.

Offshore wind turbine farms, such as those in Europe and China, are generally built by driving a single pile into the seabed, but it is hard to predict the force of water on the structure and the effects of erosion around the base.

Works to counter the erosion and prevent the wind turbine collapsing can cost upwards of $200,000 for each foundation. Guo said although more research is needed, the model and solutions can be applied to design the piles and predict their safety based on erosion depth.

He said the safety of existing buildings supported by piles that are constructed near deep excavations has been an issue in many metropolitan areas, such as New York, London, Taipei and Shanghai.

“The safety essentially depends on the force and bending induced in existing piles by soil movement; this can also be predicted using the same math model. For example, if a person builds a house by the waterfront they may experience the situation where the embankment can slide.

“The damage can cost about $10,000 per metre to repair, which is very expensive for the home owner. It would be much better to be able to design a cost-effective solution to avoid those costly repairs in the first place,” he added.

Guo, who works with the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering, said the work will also help develop new types of piles that could further reduce construction costs by as much as two-thirds.

“When the large tsunami struck Japan in 2011 the force of the waves lifted the protective coastal rock walls and they floated away,” he said.

“Anything in their path, including people’s houses, was smashed by these floating concrete projectiles.

“During the Christchurch earthquakes a major problem was the soil that tuned to liquid, what we call liquefaction, and the fast flow of liquefaction erodes the soil under foundations supporting buildings and bridges, causing them to collapse.

“In both cases we can use the model to predict the force and design piles strong enough to resist collapse.”