Less than 6 weeks after we saw the Tank Bay demolition, shortly after 10am on Saturday 27th February 2021, we saw the planned collapse of the Boiler Bay, initiated once again using explosives by leading UK demolition contractor; Demolition Services, led by CEO Jenna Romani.
Demolition Services are now considered to have concluded the Boiler House demolition at Ironbridge Power Station with the Boiler Bay being the 3rd and final explosive demolition event we have seen on the structure. In July 2020 we had initially seen the Bunker Bay collapse weighing in at 6,000 tonnes and earlier this year, the Tank Bay around 5,000 tonnes.
This final structure stood at 58m tall and 112m wide, housing two of the stations former boilers. Its demolition is expected to generate 20,000 tonnes of recyclable material. A considerably larger structure that we have seen so far on the site, further constrained with the location of the live 400kv substation less than 40m away.
While the demolition itself appears to be a mere number of weeks after the Tank Bay, it is clear that its planning has been ongoing for some time and is testament to the project management team ability to facilitate this dual planning process.
The pre-weakening design of the boiler house was one of the most complex challenges to be overcome on the site so far and the Engineers worked tirelessly to ensure its design stood up to independent checking and external critique.
The risk of premature collapse was always at the forefront of everyone’s mind and the extent of this scrutiny and rigorous check process provided an element of assurance for all involved.
One thing that became apparent during the design checking process was the obvious desire to design out any risk of premature collapse as the industry strives for improvement.
As the Engineers worked to meet this natural desire and having made a number of suggestions it became clear that although the pre-weaking design had long improved from those historically seen and those of its competitors, ultimately, whilst the risk could be reduced, it was not considered possible to eliminate the risk entirely through design.
Recognising that the risk of premature collapse could not be eliminated by design, the team identified that the quality of workmanship was of paramount importance, in reducing the likelihood of any premature collapse and went about exploring the parameters and tolerances, that could have later been applied to the quality assurance checks carried out on each of the cuts.
Following lengthy discussions, the team concluded that it was not considered possible to measure the accuracy of a cut using a numerical value, series of values, using a measuring gauge and or by applying a series of numerical parameters.
The common outcome when executing the accuracy of the horizontal flange cuts however was to achieve even bearing on the shims. It is this even bearing, that contributes to the stability of the structure in its pre-weakening state.
With the best pre-weaking design, cut detail or marking up system, even bearing could only ever be achieved through cut accuracy which came from the skill of the burner and the workmanship during the works.
Having explored this in more detail, having allowable tolerances, pre-determined for the cut itself, did not alter the quality of workmanship required as there was little opportunity for change once the cut has been completed.
Experience is therefore unquestionable, more so when in doing the blast cuts and a dynamic assessment is continually being made to ensure that sufficient and even bearing has been achieved with the cuts and how the building is reacting in its pre-weakened state.
Offering the ultimate layer of protection in carrying out the pre-weakening works, Demolition Services had in place a ‘stop the job’ policy. This meant that ANYONE could exercise the right to stop the job if they consider themselves or anyone else to have been at risk. This concern could arise from an opinion or measurement over the accuracy of cuts being carried out or simply a gut feeling.
DSL have confirmed that their Quality Management Plan meant that any ‘stop the job’ request, irrespective of its reason would be fully investigated by DSL and only following satisfactory sign off would work be permitted to recommence.
Demolition Services established a robust Quality Management Plan ahead of the Bunker Bay demolition which saw each and every cut being allocated a unique number, later referred to as the cut number. As ambassadors for ‘knowledge share’ within the industry, they go on to confirm that, this cut number was tracked through the works as time and date stamped photographs were taken once each and every pre-weakening cut was physically marked up on the steelwork through to evidencing the completion of the cut.
The process of pre-weaking relies therefore heavily on skill, experience and knowledge and Demolition Services, using competent burners had previously demonstrated the degree of accuracy needed already at Ironbridge Power Station of which resulted in the successful collapse of both the Tank Bay and the Bunker Bay.
Whilst Demolition Services have adopted a cautious approach, going above and beyond in ensuring the successful demolition of the Boiler Bay, it is clear that they have a desire to improve the demolition industry as a whole by encouraging and participating in knowledge share whilst offering guidance on future pre-weakening projects.
Demolition Services recognise the expertise and contributions made by Structural Engineer; Rob Clarke of Richter Associates, Explosives Engineer; Ian Beasley of SES and Structural Burner; Tim Arnold, at Demolition Services that we can celebrate the success of completing the demolition of the Ironbridge Power Station, not forgetting the many more team members that make such an event possible.
The ability to complete the demolition of a power station is unquestionably a niche in what is already a specialised industry and Demolition Services have without a doubt, surpassed all expectations.