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Demolition engineering and methodology for the removal of two chimneys at Scunthorpe Steelworks.
Due to their location and construction one chimney was demolished using a push down methodology and the other was demolished with a blow down methodology.
Demolition Contractor – Sam Evans and Son
Explosives Contractor – Specialist Explosive Services
Client – British Steel
Pull down and blow down methodologies are high risk but for a very short period of time. This risk can be managed with controls such as site exclusion zones.
The philosophy behind these methodologies is to get the structure on the ground as quickly as possible to be processed by heavy machinery at ground level. This methodology reduces the overall risk compared to methodologies that require working from height for prolonged periods.
Chimney 1 – Push Down
The first structure was a steel stack 5m in diameter and 56m tall with an outer shell and an inner liner with a significant change in diameter approximately 5.5m above the base.
The main site constraint for the push down was the proximity of an Ammonia tank (pictured) This was a principal risk, which meant the design concept had to ensure the structure fell away from the tank.
The design and check was based on the justification of pre-weakening and assuring that there was enough structure to resist destabilising forces such as wind loadings.
The structure was pushed down with an open grab atachment on the end of an excavator to ensure and accurate push and limit the risk of the attachment slipping on the curved surface of the chimney.
Chimney 2 – Blow Down
The second chimney was 78m tall and almost 1,000 tonnes in self weight.
The structure consisted of a concrete outer ring and a brick internal liner. There was also a large flue opening that had to be incorporated into the design and pre-weakening sequences.
The demolition methodology was to ensure that the chimney fell within the safe zone and away from live assets such as the British Steel converyor lines.
The design and check consisted of a review of each stage and checking the stability of the different sections until the final section was blasted out to induce a controlled collapse.