The demolition methodology involving the use of explosives to cause the deliberate collapse of a structure is typically referred to as a ‘blow down’
An advantage of using a blow down demolition methodology is that effective use can significantly shorten project timelines compared to progressive or top down demolition.
A potential limitation to the use of this methodology is the requirement for sufficient space around the structure.
This method is common on large disused industrial demolition projects where there is a large site footprint.. Andun have provided demolition engineering support on blow down demolition projects including power stations and Steelworks.
Blow Down Demolition Methodologies
A common misconception is that the use of explosives in demolition actually blows the structure apart.
For blow down demolition, the explosive is used to trigger the collapse of the structure by weakening or removal of key structural elements, allowing gravity to do the rest.
Planning the deliberate collapse of a structure requires a strong understanding of the structure and experience of how structures behave in extreme conditions. The approach for steel and concrete structures is different.
Steel structure Blow Down
The first step is to pre-weaken the structure
This can include cutting out bracing and secondary beams. Sit cuts and hinge cuts will be formed in the column sections to ensure that the structure collapses as required. The final cuts should be made only when everything is ready.
Explosive is then used to provide the trigger to cause the structure to collapse, generally by knocking out columns. These works need careful planning to minimise the risks of working in a weakened structure.
However, the use of cutting charges (shaped charges) is becoming more commonplace, reducing the risk of undertaking the final cuts.
Concrete Structures Blow Down
To prepare concrete structures key structural elements are weakened.
Explosives are typically placed in holes pre-drilled into the key elements that are to be fragmented. Once detonated the solid explosive converts instantly to a gas of much higher volume which effectively blows the concrete off the reinforcement and gravity does the rest.
Andun have provided demolition engineering support for a wide range of projects including a number of structures at the decommissioned Eggborough Power Station which have been covered by local and national media outlets.
Blow Down Case Studies
The following case studies are available on our website