Tire Soil Mixture Can Protect Buildings From Quakes

Researchers in Hong Kong and India are working on mixtures made of tire rubber crumb and soil/sand that when placed beneath and around a building foundation, can help the structure resist earthquake tremors.

In a study by the Indian Institute of Science (IISc), a team of researchers conducted several experiments to come up with the right mixture of sand and tire crumb. So far the study a found a combination of 75 per cent tire crumb and 25 per cent sand to be effective in reducing vibrations of seismic waves and mitigate the seismic impact.

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“Our studies show that the sand-rubber mixtures can reduce the earthquake impact by 40-50 per cent in comparison with conventional soil fill for low to moderate rise structure,” Anbazhagan, an assistant professor at Department of Civil Engineering at IISc, said.

However researchers, worried that 75 percent tire rubber content might affect the stability of the building, are considering adding reinforcements and altering the composite material, Anbazhagan said.

The study found that the mixture of sand and tire crumb act as cushions, absorbing the sliding forces parallel to the ground. Imparting flexibility to the structure due to cushioning action of tire crumb sand layer, not only reduces the seismic load, but also reduces the permanent displacement of the structure, the study said.

As part of the study, IISc researchers also propose a geotechnical isolation system using rubber-sand mixtures, that rests above the ground water table.

“Evidence shows that rubber present above ground water table does not contaminate the water table, Anbazhagan said.

Civil engineers at IISc said this new technology, when developed, will have two important benefits: build earthquake resistant buildings that can potentially save lives during a disaster and provide an alternative use for tire derived crumb rubber.

Geologically, India is a huge plate that is going northward at a pace of about 50 millimeters every year. Indian plate boundaries are capable of producing moderate to mega earthquakes, making more than half of India, by area, vulnerable to earthquakes, according to geologists.

Hong Kong Also Working on Earthquake Cushion

In Hong Kong, researchers at the University of Hong Kong have developed a low-cost earthquake “cushion” made of soil and tire chips that form a layer below and around a building’s foundation and reduce earthquake shaking by 50 percent on average, according to the university’s in-house computer simulations.

Recently named a finalist in the Asian Innovation Awards, the Earthquake Cushion acts as a buffer between earthquake waves and a building. The rubber in the cushion attracts seismic waves and damps them. Rubber, known for its energy absorption, is often used for vibration control and to dampen automotive components, the researchers said.

“It’s a lot like the airbag in a vehicle, which prevents occupants from striking the interior objects,” Dr. Hing-Ho Tsang, principal investigator behind the cushion, also called the “Geotechnical Seismic Isolation System,” said.The cushion dissipates seismic energy before the waves reach a building’s foundation.

“This differs from the traditional earthquake proofing-like laminated rubber bearings-which are installed between a building and its foundation. As a result, the bearings are a part of the structure and seismic waves can still potentially damage a building before they are dissipated, Dr. Tsang said.

The earthquake cushion is still going through preliminary tests to gauge its effectiveness and safety before it is used on buildings.

To date, the university has run computer simulations that track the cushion’s performance against actual earthquake models, including the 7.8-magnitude earthquake that struck Chile in 1985. Researchers varied the number of building stories and width of the cushion. In all cases the cushion effectively reduced both horizontal and vertical ground motion by 40-60 percent.

Hong Kong University researchers found the cushion is most effective when it is at least 5 meters thick and used for medium-rise buildings between five and 20 stories. They have not done simulations on buildings taller than this so have not confirmed if there is any limit, Dr. Tsang said.

In 2009, the University of Hong Kong lined up with a research group at Central South University in China to conduct a small-scale shaking table test, simulating the weight of one and two story houses respectively, which confirmed the computer-based results.

The next challenge: conducting enough successful experiments to get the “skeptical construction industry” to accept the innovation, Dr. Tsang said.

© Scrap Tire News, December 2015