Geologically, India is a huge plate that is going northward at a pace of about 50 millimetre every year. Indian plate boundaries are capable of producing moderate to mega earthquakes. No wonder, by area, more than half of India is vulnerable to earthquakes, making the lives of about 200 million city dwellers more risky. Buildings that can withstand the jolts during an earthquake can go a long way in saving lives.
Motivated by this, a team of civil engineers from the Indian Institute of Science studied if tyre crumb can be used to construct buildings that can withstand earthquakes. A tyre crumb is a granular material recovered from recycled waste tyres. Studies revealed that a mixture of tyre crumb and sand, when placed beneath and around a building foundation, can help buildings resist the jolt.
“When rubber tyres are filled with small stones (rock aggregates), they can absorb up to 70% of the earthquake’s forces”, explains Anbazhagan, Assistant Professor at the Department of Civil Engineering, Indian Institute of Science. His team is focussing on methods to reduce an earthquake’s impact, and using tyres for the purpose.
They found that the mixture of sand and tyre crumb served as cushions, absorbing the sliding forces parallel to the ground.
Interestingly, imparting flexibility to the structure due to the cushioning action of tyre crumb sand layer not only reduces the seismic load, but also reduces the permanent displacement of the structure.
The team conducted several experiments to come up with the right mixture of sand and tyre crumb and found that a combination of 75% tyre crumb and 25% sand to be the best composition. “Our studies show that the sand-rubber mixtures can reduce the earthquake impact by 40-50% in comparison with conventional soil fill for low to moderate-rise structures,” remarks Anbazhagan. The team hopes that this solution can withstand earthquakes of all magnitudes. At present, this idea is in its infancy.
Earthquake resistance aside, could this new technique possibly pollute the soil and ground water? “Not likely”, Anbazhagan says. “Evidence shows that rubber present above ground water table does not contaminate the water table. In this study, we propose a geotechnical isolation system using rubber-sand mixtures. This rests above the ground water table”, he explains.
This is definitely a cost-effective means to save lives and economic loss in the event of earthquakes, in addition to achieving a cleaner environment. Anbazhagan’s team has taken a step towards a cleaner and safer future.
