Countdown begins for Supertech towers: Anatomy of an implosion
NOIDA: The two 32-storey towers of Supertech Emerald Court (Apex and Ceyane) in Noida will be the tallest ones to be demolished in the country so far.
Experts say that the country is fairly new to the concept of highrises and there is little expertise or experience in their demolition. While there are a few different techniques for demolition, the technique of “implosion” is most used and best suited for demolition of such tall structures in a densely populated area. In this technique, small explosive devices are placed at multiple locations in the building in a manner that the debris falls within the premises.
After being admonished by the Supreme Court regarding delays, the builder and Noida Authority have finally assigned the task of demolition to Edifice Engineering earlier this week. HT speaks to partner, Edifice Engineering, about how this piece of history will unfold.
Uttkarsh Mehta, So, when are the buildings coming down?
According to the action plan that we have submitted to the authority and the builder, once we have the work order and all the paperwork is complete, we will start our survey on the ground and the preparation will take about three months. We are hoping that the day will be sometime around mid-May. After the blast, it will take around three months for us to clear the debris.
What are the preparations that you need to do now?
There are two kinds of preparations – one is preparing the building or structure itself and the other preparation is for the neighbouring buildings or to the surroundings.
We also need No Objections Certificates (NOCs) from all involved authorities like the DM, police, fire department. We also need a clearance from Petroleum and Explosives Safety Organisation (PESO) in Agra to transport and use the explosives. Additionally, we have to run a campaign to inform all the people in the neighbourhood about Dos and Don’ts during the blast. We will also have continuous meetings with all government departments to prepare an evacuation plan for all those living within 50 metres radius and for the halting of traffic in 250 metres’ radius for the blast duration... All this will be done in consultation with Central Building Research Institute.
What does the blast involve?
After the survey, our expert will prepare a “blast design” for the structure to fall from all perspectives such as safety, vibration and other factors. The design will answer questions like which columns have to be blasted? Which walls have to be removed beforehand? At what floors the explosives will be placed? What will be the diameter and depth of the hole (in which they are placed)? What is the quantity of explosives needed? The building has to fall straight down like a pack of cards with minimum flying debris. That’s our biggest challenge.
Maybe after a month of starting the survey, we will be able to decide on a blast date in concurrence with all authorities. Prestructural analysis of all building in the radius of 50m will be done. We will survey for any existing damage to any of the structures and we will be checking them after as well to see if there was any impact of the blast.
There are apprehensions among people who live close by, especially in Emerald Court that is about 9m from the twin towers. What will be done to ensure safety?
From our initial analysis of the location, we will have to build a passage between the twin towers and Emerald Court to avoid any flying debris. When we saw the site, there is a driveway between the two buildings that is already weakened. It has cracks and exposed reinforcement. We may have to remove the driveway entirely so that the debris falls straight in the basement. The driveway will then have to be reconstructed later... Additionally, we will use empty containers anchored to the ground and stacked up to the height of three floors as an additional safety layer to protect the Emerald Court buildings from any flying debris.
What other safety measures will be followed?
We use at least four layers of geo-textile fabric or cloth to cover the entire building so that there is no flying debris. Every part of the building to be blasted will be covered with wire mesh and then with geo-textile fabric... A layer of the cloth will also be placed to cover the entire building.
For ATS and other buildings in the surroundings, we will cover them with geo-textile fabric as well, which is mostly for dust control. Our assessment is that there will hardly be any flying debris that will leave the compound.
During such implosions there is a large dust cloud. Is there a way to control dust?
Yes, there is a dust cloud and it is the only negative thing about this technology. While doing an inward blast there is a huge dust cloud and it usually dissipates in 6-7 minutes. How much time it will take to dissipate and how far it will go also depends on the wind speed and wind direction at the time of the blast.
However, there is no way to control or minimise it from our practical experience. Fire tenders, mist guns and other solutions have been tried but have only been about 10% successful.
We will ask the Noida Authority to be ready with mechanical sweeping machines. While sending advisory to neighbouring residents, we will mention that they should keep all doors and windows closed, switch off their ACs and keep the external unit of their ACs covered if possible so that the dust is not sucked in.