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“When the 3,700 kg of explosives went off, I said ‘thank you, lord’. We are all very emotional right now… Placing different explosives at different places, deciding magnitude and mass of these — all done to minimise damage… it was challenging,” said Jet Demolition managing director Joe Brinkmann about the Supertech twin towers demolition on Sunday. Over 3,700 kg of explosives was used, and the explosion was carried out with the waterfall implosion technique.
“We can’t blast everything thumbs down. It has to be in a way that all rubble falls a bit distant from each other. If we dropped everything straight down, the rubble would have fallen at much more distance, impacting buildings and lives. Also, there would have been a higher ground vibration and higher air blast,” said Joe.
For the South-African company, the Supertech towers is their second biggest project (in terms of the height of the building). The biggest demolition was the one in Johannesburg in 2019 — the company demolished the Bank of Lisbon, a 108-metre-high building, in less than 30 seconds. However, Joe and his team had much more difficulty demolishing the Supertech towers that are nearly 100 metres tall. “It’s weird because the closest building to the bank was hardly 7.8 metres. In Noida, the closest building was 9 metres but it was still a difficult task. Here, we have a robust concrete structure filled with steel reinforcement,” said Joe.
The company worked closely with Edifice Engineering, the firm in charge of the project. Edifice’s partner Utkarsh Mehta called the explosion ‘a planned fall’. “We were apprehensive that rubble will touch the ATS tower compound wall as the twin towers are oblong shaped. The wall was damaged but that was it. The closest building being 9 metres away from the towers was not damaged. We had anticipated the rubble will fall towards ATS and on the roadside, and the results were the same. The ATS building is safe. From tomorrow, excavators will be used to remove debris. Two are already in place. Since the size of the rubble is big, it will be first broken down into smaller pieces. It will then be segregated. Pure concrete will be sent to one plant and steel to another. Over 100 workers will be deployed every day,” he said.
The explosives used
Officials said different types of explosives with different masses were placed in the towers. “As per our calculations, we placed them differently and strategically. Mainly, PETN and emulsion explosive were used. We need to match explosives with the breaking effect. In some special areas, the emulsion was used. In the building, lower floors have more reinforcement. As we are drilling specific holes, so usually PETN is used, but emulsion is also used to fill holes better in lower floors,” said Jet Demolition managing director Joe Brinkmann. Similarly, explosives with more mass were placed on the lower floors as those have stronger columns. On the upper floors, fewer mass explosives were placed. Other types of explosives used were Solar coal. Electric detonates and shock tubes were also used. The tubes were placed in a way that some had a 0.5-millisecond explosion capacity, while others had a 7,000-millisecond capacity.
Edifice claimed 9 metres of the boundary wall was damaged at ATS. Nearly, 900 bricks and several windows were also damaged. Edifice will be working with the Ramky Group for debris management. The latter has a plant at Noida Sector 18, where all debris will be collected and processed to make blocks, bricks or slabs.
“When 60% of Ceyane tower was down, Apex building started crumbling. Everything happened in 10-12 seconds. The debris is not even two floors tall as it is scattered. None of the parks or residential areas were damaged,” said Mehta.
His team put over 10 black boxes and 70-80 crack gauges to study the damage on Emerald Court and other buildings. “We have analysed three crack gauges, and the cracks which were there before and today were almost the same. Since no debris went there, there can’t be damage,” added Mehta.
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