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Dynamite or Excavator? Determining how to down edifices

By Peter Theuri | February 25th 2021

The building that was being demolished but came down faster than expected almost killing one person in Kasarani, Nairobi. [Jenipher Wachie, Standard]

On Tuesday, February 17, Trump Plaza Hotel and Casino went crashing in a sea of dust and debris, a loud staccato of explosions tearing into the cold morning air as a small crowd cheered.

3, 800 sticks of diamond exploded and in under 20 seconds, the Atlantic edifice, once owned by former United States’ President Donald Trump, was a pile of rubble.

This is called controlled demolition, where explosives are let loose to perform final rites on a building which has outlived its usefulness.

The video of the demolition that was circulated on social media was short, barely thirty seconds, but it went truly viral, especially on twitter. To some, it was because of the popularity of the building’s former owner. To others, it was purely because of how the demolition unfolded.

It was smooth. It was professional. And apart from the materials that were used to construct the tower and probably the building’s irate owners, there were clearly no accidents, no unintended casualties.

Kenya has had its fair share of famous demolitions in the past few years, the last occurring some three years ago.

 In 2018, there was planned a raft of demolitions that would affect up to 4, 000 buildings built on riparian land in Nairobi alone.

According to a task force appointed by President Uhuru Kenyatta to clean and reclaim Nairobi River, among other rivers, the buildings would be pulled down within just a short time.

The Nairobi Regeneration Team took some prime establishments as their first casualties, including Southend Mall along Lang’ata Road. Shell petrol station in Kileleshwa, along with the popular Java restaurant, a tenant of the station, were also brought to their knees.

But unlike what happened in the United States, where critics of former President Trump booked front row seats to watch Trump Plaza Hotel collapse within seconds, the Kenyan authorities mowed down the houses using bulldozers and excavators.

Pushing at walls, tugging, and knocking, the demolition was a noisy affair, less spectacular than what the explosion using dynamite was. And although the demolitions are not particularly very lovely affairs, they can look extremely shambolic. Sometimes, here, they did look just that.

Just a year later, in 2019, Principal Secretary in the State Department of Public Works, Housing and Infrastructure Paul Maringa said that Nairobi and Mombasa faced a serious threat of substandard houses.

''Many of these houses that have been audited are not fit for human habitation,'' he insisted, paving way for further demolitions.

The PS observed that a total of 12,185 houses in different parts of the country had been audited to ascertain their suitability for habitation, with over 7, 300 put up on road reserves and railway reserves now fresh in the sights of demolishers.

If this indeed happens, we might have the same machines we have previously had doing the dishonourable honours of demolishment, as Tom Oketch, the Chairman of the Institution of Construction Project Managers of Kenya says that we are “not yet there” technologically.

“We do not have the capacity. We are not yet at the level of using explosives. We lack the contractors to do so and the technology to enable this,” he says.

Silvano Inyangala, a project manager at Superior Homes Kenya, agrees with Dr Oketch, saying that controlled demolition’s lack of adoption in the country could be as a result of a lack of local expertise.

“This technology seems not to be available in Kenya, or probably local expertise on how to use it is not sufficient.”

But perhaps, says Mr Inyangala, standalone buildings could make do with this new technology in the near future, which is faster and safer, as we tap into the technologies others have succeeded in.

“For standalone buildings with neighbouring properties at far away distances, the dynamite implosion mechanism seems safe”

Controlled demolition employs a series of small explosions, strategically placed within a structure and progressively detonated, encouraging a collapse by weakening or removing critical supports.

“Explosives on the lower floors then initiate a controlled collapse and the building fails under its own weight, succumbing to gravity,” writes Hughes and Salvidge, a UK decommissioning companies who “demolish, crush, and recycle”.

Kevin Maina, an assistant engineer at Losai Management Limited, says that the process of setting up the explosives for the systematic implosion of buildings is time consuming, one of the reasons why it is not a very popular method locally.

“Although the actual demolition is quick, preparing the condemned structure

for building implosion can be extremely time consuming, with larger structures taking as long as six months to prepare as highlighted above. Therefore, implosion demolition is not a feasible method for demolishing residential structures and can optimized for larger structures like smokestacks, stadiums and skyscrapers.”

The local method, the one we are used to, is mechanical demolition, described as any demolition work that uses powered mobile plant (such as excavators, cranes, loaders and bulldozers). This method is typically used on buildings reaching a height of about 66 feet (8-storey building).

“The machine systematically knocks down the building from top down while another ground crew removes the rubble while spraying the site with water to control dust. This method is quick, efficient and relatively tidy when performed by a skilled operator,” says Engineer Maina. .

This mechanical demolition involves a base machine, excavator, equipped with a long telescopic boom for demolition where a demolition tool, hammer, is fitted to the arm-end and is used to break up the structure from top down while another ground crew sorts out the debris for disposal.

“A successful demolition takes into account factors such as space availability to accommodate loose debris pile, and usage of the minimum charge weight of explosives. The process should also take into consideration the containment of the fragmentation to avoid negative effects on the adjoining structures, and should as well consider dust control measures,” he says.

Engineers first determine whether the building will collapse via implosion or mechanical means after structural analysis.  They then ensure that the demolition method adopted proves to be more economical and safer.

Perhaps we will be seeing more of controlled demolitions locally, especially as most of the 4, 000 buildings reportedly earmarked for demolition in 2018 remain standing. Or maybe we are still not yet there and our bulldozers, cranes and excavators will have some nudging to do to flatten buildings that have to come down in the future.

Striking a balance between cost and safety, and maybe time, is most crucial in demolition. All the difference there is between a spectacular and a not too safe demolition.

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