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World record: ring net stops 16-tonne concrete block
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Geobrugg celebrates a new world record.
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Geobrugg has tested its new RXI-500 high-energy ring net rockfall barrier, constructed to withstand impact energies of up to 5000 kJ, in Walenstadt. To generate an impact energy of 5000 kJ, a concrete block 1.90 metres long and weighing 16 tonnes had to be dropped in freefall onto the rockfall barrier from a height of 32 metres. This event was the ’acid test’ in the certification procedure of 25 October 2006, undertaken by the EKLS Federal Expert Commission on Avalanches and Rockfalls.
The boulder, painted yellow and black, was released, and fell straight down towards the ground in what seemed like slow motion. It reached 90 km/h during its 32-metre fall. For a split second it came to a dead stop, then the concrete colossus landed safely in the net. The steel weaving (ring net) had held. The success was a world premiere. The previous heaviest stone that had been caught by a ring net was considerably smaller, weighing ’only’ 9,640 kg.
Werner Gerber, project manager at the Federal Research Institute for Forests, Snow and Countryside, photographed the flight and the collision. The cameras he used shot pictures at a rate of 250 per second. The 13 load cells installed between the ring net and the cliff provided him with 30,000 measurement readings per second. When he finished his calculations he knew exactly how long the stopping distance was, where the forces were particularly strong and how much energy was absorbed by the ring net.
The 16-tonne block stretched the ring net a good seven metres downwards – Gerber is satisfied. He will return to Walenstadt once again to award the system its certification.
(the system was officially certified in October 2006.)
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