NOIDA: What does it take to raze 30-storey buildings rising over a cluster of societies with pinpoint accuracy? A study of the structures, their distinct features, a calibrated use of explosives and painstaking preparations for months to make sure the entire exercise was backed by science and was ultimately safe.
The masterminds of the demolition told TOI on Sunday that the biggest challenge for them was to bring down the towers without damaging the nearby apartments, the nearest being just 9 metres away. The recognition that thousands of houses were at stake was what drove the implosion blueprint, said Joe Brinkmann, the director of Jet Demolition and architect of the blast design.
First, the experts analysed the buildings and realised they were stronger than 30-storey structures would typically be — partly because construction in an earthquake-prone zone (Noida is a Seismic zone 4) requires the foundations to be sturdy, and also because the towers were originally planned to be 40 storeys high.

“Every building is different. Our technical team here studied every aspect of the buildings and where they were standing. The towers were robust,” Brinkmann said.

A test blast in April also gave them an idea of the strength of the columns in the towers, Apex and Ceyane. A decision was taken at that time to use an additional quantity of explosives, and change the blast design, now including more floors where the incendiaries had to be strapped.
And so, the quantity was finalised at 3,700kg of explosives across 9,642 holes in the columns of both the towers.
In pics: Noida’s twin towers reduced to dust cloud
“It was important to direct the collapse away from the next-door buildings in a controlled manner. We didn’t want it to fall straight as the debris would have flown on all sides. We also didn’t want the towers to go down at once. The blast design was such that the floors capitulated inwards, like a waterfall, to reduce ground vibrations,” Brinkmann said.

The nature of explosives and their placement, too, was crucial. “Primarily, we used PETN, a chemical compound that is also used for explosives in mines. We used the shock tube system, emulsions and non-electric detonators before placing them in holes. A series of detonations were timed perfectly to bring the desired disruption and subsequent the fall of the buildings,” said Kevin Smit, the senior site manager who oversaw and monitored implementation of the blast design on the ground.

To this, Brinkmann explained that PETN was strategically used on the upper floors, while emulsion-based explosives were added to it on the lower ones. “The columns are stronger as you go down the buildings. There are more reinforcements and more concrete is used. We drilled holes of specific sizes and loaded them with a specific amount of explosives, depending on the density of the reinforcements and strength of the column,” the “master-blaster” added.

To get the cascading effect, the detonations were also delayed, between 17 milliseconds and 200 milliseconds, officials said, adding that it was similar to how they brought down the Maradu apartments in Kochi two years ago. Jet Demolition and Edifice Engineering had partnered in the January 2020 project as well.

“There were two types of delays — one is surface delay and another is down the line. We had a lot of room to play with the delays to execute the waterfall implosion. This was the same system and the same explosives that were used in the demolition of Maradu apartments,” Smit said.
Edifice Engineering, the Mumbai-based company that was responsible for the entire operation, said everything went according to plan.
“There was no damage to the nearby buildings as the towers fell according to our predictions. Some windows in neighbouring buildings cracked, but this was expected,” said Mayur Mehta, project manager at Edifice.