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Witnessing earthquake inspires young engineer to soil research

3 December 2015
According to postgraduate research student Wang Shengzhe from the University of Sydney’s School of Civil Engineering, our understanding of soils’ behaviour is still minimal

After living through a 6.5 magnitude earthquake in the New Zealand capital Wellington in 2013, 23-year-old Wang left his structural engineering role with a professional consultancy to take up a research degree into soil movement, in the hope of preventing future disasters.

Our safety could be dependent on understanding the behaviour of just a few grains of sand
Wang Shengzhe, postgraduate research

After thousands of years constructing massive buildings and monuments you would imagine scientists understood the behaviour of the ground we stand on.

 

“Our safety could be dependent on understanding the behaviour of just a few grains of sand,” says Wang.

“My research examines how soils respond under extreme conditions, such as earthquake, especially when this behavior is further complicated by the introduction of pore water.

Wang says soil strength can change under impacts from sources including heavy machinery operation, pile driving, explosions or earthquakes. This could have disastrous consequences such as the manifestation of soil liquefaction.

“Liquefaction is when wet soils completely lose their strength because of an excessive build-up of water pressure due to the ground shaking,” he explains.

“The 2011 Christchurch earthquake in New Zealand produced this type of phenomenon. The entire city saw widespread damage resulting from massive amounts of soil liquefaction.

“So it makes sense to avoid constructing buildings on ground with extensively saturated soil prone to liquefaction, or you must have plans for soil remediation such as draining the ground.

“By adequately understanding the liquefaction potential of soils when planning cities and suburbs, we will know exactly where and where not to construct our facilities and place our most critical infrastructure.

“This could potentially save lives and billions of dollars in repair costs,” he says.

A motivator for Wang’s research is his Wellington earthquake experience.

“I was on the 9th floor of the building at that time,” he says. “All of a sudden, the building swayed from side to side. I saw walls crack and books fall from the shelves. It was like drifting on a boat.”

The unnerving experience became the catalyst that encouraged him to pursue his earthquake-related research in Australia.

“I take a small soil sample and place it into a machine. I then subject the sample to a sudden impact,” Wang says. “This will allow sensors on the machine to feed me information which enables me to calculate the soil’s strength, or how much load it can support.”

In the experiments, Wang also made decisions about what types of soil to test, how much water to add, and what kinds of impact to subject on the material.

So far, Wang tested three types of porous material and will shortly conduct the final batch of experiments on the fourth.

Professor Luming Shen, Wang’s PhD supervisor says the team’s aim is to understand the interaction between water and soil particles and to highlight the need for the consideration of soil liquefaction in the building and design codes of countries with frequent earthquake activities, including China.

Wang’s research will be first of its kind to systematically investigate the effect of particle size distribution, particle shape and water content on the behaviours of porous media under impact loading.

This research will reveal the key factor that controls the particle-water interaction in wet porous media and thus help engineers understand the physics behind the liquefaction of soil in earthquakes.

Five fun facts about soil and sand 

 

  • Soil is a living system. There are more bacteria in a handful of soil than there are people on earth. That’s over 6 billion!

 

  • The total number of sand grains on earth is approximately equal to 20 per cent of all the stars among the 200 billion galaxies making up the observable universe.

 

  • The tallest sandcastle constructed measures 14 metres – about the height of a four storey building.

 

  • Up to 50,000 square kilometers of topsoil – an area around the size of Costa Rica – is lost every year mainly due to wind and water erosion.

 

  • Contrary to Hollywood movies, the density of the human body would make it impossible to sink in quicksand. We would actually float.

Victoria Hollick

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