Military robots and 250 kg of plastic explosives have been used to bring down the remainder of the boiler house at Didcot A Power Station.
Alford Techologies acted as principal contractor on the RWE site for the explosive demolition work. The firm brought down the remaining structure at 6am on Sunday.
The company was brought in to work on the project in March, following the partial collapse in February.
Speaking to Construction News, managing director Roland Alford said his firm had been tasked specifically with developing a method to demolish the structure remotely.
He said: “To my knowledge, it’s never been attempted anywhere ever before, so we really had to start from the ground up when working out how to do it.”
The company spent months developing its plan for the explosive demolition and has invented a number of new explosive charges and connectors for use at Didcot.
It has also trained operatives to use its 10 robots to plant charges at the site.
The group received the green light to start work from the multi-agency strategic co-ordination group on Monday this week.
Plastic explosives were imported from Finland for the operation.
The robots have been made by Irish company Reamda and British firm AB Precision, with the team also using Brokk remote-controlled demolition machines and lightweight tractors supplied by the army.
Alford Technologies used the robots to carry out laser scans of the existing structure to determine its condition, before carrying and planting explosive charges onto the columns holding it up.
Different-sized robots were used in tandem to place the charges precisely.
Mr Alford said: “We used the lightweight tractor to carry the medium-sized robots, strapped onto a pallet onto site. These weigh 300-400 kg.
“The medium robot carries one of our charges, a special C-shaped charge, that it places over a girder to cut it.
“And we had a small robot on the side giving us a good perspective of that so we could get the placement accurate.
“This has really been pushing the boundaries of what’s possible and what’s been done in the past.”
The remaining structure consisted of two boiler units, which are effectively two separate, but linked, buildings.
There were six columns in total holding up the structure, in three rows of two. Speaking ahead of yesterday’s demolition, Mr Alford said the explosives would cut and kick out the middle two legs first before quickly doing the same to the outer legs on the south side of the structure.
“That will drop the building and the boiler will start moving. The building will actually hinge over the northern stanchions,” he said.
“Then there’s only one direction it can collapse in, so there’s no chance of it skewing sideways or falling towards the debris pile, which is obviously totally unacceptable.
“The whole purpose of being here is to facilitate the recovery of the three guys.”
The bodies of three Coleman & Co employees – Ken Cresswell, John Shaw and Chris Huxtable – remain trapped under the collapsed portion of the boiler house.
Another worker, Michael Collings, was found dead shortly after the collapse on 23 February.
Mr Alford also said the vast majority of his team are ex-military personnel with a “built-in understanding of grief and loss”, which has helped when keeping the families of the missing men informed of progress.
“When the families first came here they were very upset about the delays,” he said.
“When they started talking to our guys, they said they trusted us and that they believed us, because they realised that our guys take it very personally.
“For a long time we were operating in the shadows and no-one was aware of what we were doing, so it didn’t look like much was happening.
“But actually an awful lot was [being done], we were doing lots of testing and development of the charges, and our training.
“No-one’s sitting there wondering what to do – we’ve been working flat out for months now. Everyone’s just totally motivated to make this a success and do it as quickly as possible.”
RWE had written to local residents earlier this week to tell them that demolition was scheduled to take place on Sunday.
Brown and Mason will oversee the removal of material following the demolition.