Demolition in the 21st century tends to be a more refined process than it was in the past. Safety and the desire to salvage materials for recycling mean that careful dismantling is now the norm rather than the popular image of blowing things up or smashing them to pieces with a wrecking ball.
That鈥檚 not to say that explosives are no longer used. In fact, as a recent contract demonstrated, explosive demolition not only still has a role but it can also demonstrate a surprising degree of precision and finesse.
In July a team of demolition specialists carried out a complex operation to take down the main production building (MPB) at the 100-acre Avlon Works pharmaceutical processing site at Avonmouth, near Bristol.
Avlon Works was originally built by British chemicals group ICI and was operational for 50 years, from 1969 to 2019. In 2016 then-owner AstraZeneca sold the site to Avara Pharmaceutical in the hope of securing the operation鈥檚 future, but Avara fell into administration and the entire site was put up for sale.
Maynards, a Canadian specialist in industrial auctions and liquidations, is now working in joint venture with demolition consultant Divestiture to clear the site on behalf of Vancouver-based property firm Epta Development Corporation (EDC).
As Daniel Gray, managing director of Maynards Europe, explains: 鈥淲e are demolishing and recycling every brick, every building, every piece of steel, every piece of metal, every kerbstone, every road. There are 10,000 assets to sell and the ultimate aim of the project is to provide a developable platform for our partner EDC.鈥�
There are 鈥� or were 鈥� 29 buildings on the site but the biggest and most challenging from a demolition point of view was the MPB. This four-storey building was designed as a seismic structure and built to be blast-proof.
鈥淎lthough it鈥檚 only four storeys it weighed about 2,500 tonnes 鈥� it was a very tough structure,鈥� says Darren Palin, director of Divestiture.
鈥淎ll the columns were heavy steel encased in concrete. That posed a problem: did we treat them as concrete columns or steel columns? There are different methods for different materials,鈥� he adds.
These days, a four-storey industrial building would usually be taken apart piece by piece using high-reach demolition excavators equipped with a toolkit of attachments such as breakers, shears and crunchers. But the Avlon Works MPB warranted more forceful treatment.
鈥淒ismantling with excavators was an option, but it would have been much slower and far more expensive,鈥� says Palin. It was therefore decided to bring the building down with explosives and then use excavators to pick over the pieces.
The MPB was as wide as it was tall, which posed another conundrum for the team. 鈥淚f we鈥檇 simply dropped it, it would have just flat-packed like a box and compacted,鈥� says Palin. So he proposed cutting the building in half down the middle so that it collapsed outwards over a wider area.
Divestiture physically saw-cut through the roof and all the floors from one end of the building to the other, leaving a 500mm gap to ensure a clean separation between the two halves. 鈥淭he floors were steel profile decking with concrete on top 鈥� really tough 鈥� so we had to use road-saws to cut through them,鈥� says Palin.
To prevent a premature uncontrolled collapse, Divestiture fixed 拢25,000-worth of temporary steelwork to prop the building up. It then set about pre-weakening the supporting columns.
鈥淲e used demolition robots fitted with breakers to remove the concrete from the steel columns and then used torches to cut partly through the steel,鈥� says Palin. 鈥淚t was a very surgical operation.鈥�
At last, the building was ready for the final, explosive, phase of the demolition. This was carried out by Sheffield-based Precision Demolition Company (PDC) using what Palin believes was a pioneering technique.
Instead of fixing charges directly to the exposed steelwork, PDC placed a 1,000-litre water-filled IBC tank alongside each of the 44 main columns with the explosives placed inside the IBCs. A total of 300kg of explosive was used.
This set-up had two effects: first the explosion instantly vapourised the water in the tanks, capturing nearly all the dust. Secondly, the hydraulic action of the water concentrated the force of the blast onto the steel columns.
鈥淚t allowed us to reduce the amount of explosive required,鈥� says Palin. 鈥淭his is the first time this method鈥檚 been used 鈥� as far as we know 鈥� but it鈥檚 something the team is going to do more often. Reducing the amount of explosive is very beneficial.鈥�
Palin acknowledges that mechanical methods are now generally preferred to explosive demolition. 鈥淪eventy-five to eighty percent of tower blocks are now demolished with high-reach excavators. These days they can reach up to 65m. We used to always blast them.
鈥淎nd although Avonmouth could have been done with excavators, it didn鈥檛 make sense. It took us about six weeks of preparation leading up to the blast but we estimate it would have taken about 24 weeks to achieve the same result with excavators.
鈥淪ome of the steel was just too big to cut with shears; we would have had to use manual cutting methods working from man-baskets. And that鈥檚 more dangerous,鈥� he adds.
Explosive demolition was the ideal solution on this site but, as Palin admits, it might not be so attractive on a site that doesn鈥檛 have the luxury of a hundred acres of space.
The demolition of the MPB was the climax of the project for Maynards and Divestiture. At the time of writing four auctions had already been held and a fifth is scheduled for the end of this month (September).
The project is so large that Maynards鈥� asset list runs to 144 pages and comprises more than 10,000 items; the spares inventory alone is valued at more than 拢2.5m, says Daniel Gray.
With the site cleared and all the assets disposed of, Maynards will hand the site over to its client, EDC, which plans to build a new logistics park with four warehouses totalling 1.85 million square feet of space.
Who鈥檚 behind Divestiture?
If you haven鈥檛 heard of Divestiture before, you might be more familiar with the name of the man behind the business, Darren Palin.
Palin spent seven years, from 1999 to 2006, at the helm of Controlled Demolition 鈥� at one time arguably the UK鈥檚 best-known demolition specialist.
Controlled Demolition finally went under in 2010 following a failed management buyout.
By that time, however, Palin had left to run Euro Decommissioning Solutions until that business was sold to Silverdell. When Silverdell went into administration in 2014 the EDS business was sold off and has since become part of Eless Decommissioning Services.
Palin launched Divestiture straight afterwards to focus on dismantling and recycling. 鈥淲e鈥檙e not 鈥榩ure鈥� demolition in the old sense,鈥� he says. 鈥淎s the company name suggests, we basically 鈥榙isinvest鈥� on behalf of our clients; we go in there and close the site down for them.鈥�
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