Demolition of 105m steel stack and supporting structure
Delta Group was contracted by BHP Billiton for the demolition of a 105m steel stack and its supporting ductwork structure at their redundant Hot Briquetted Iron Plant, Boodarie, Port Hedland, Western Australia.
Due to the close proximity of surrounding Alinta Gas Plant assets including transformers and gas turbines, Delta assessed the options of demolition and adopted the methods of felling, shearing and skidding as being the safest and most practical options, reducing the exposure to high risk activities.
For the 105m high, 11m diameter, 750t weighing steel stack Delta engineered a specialised steel bracing concept working along the fulcrum line, allowing for the even distribution of weight and a reduction in pulling capacity. The stack felling occurred on 29th October 2013 and was text book with below allowable levels of vibration.
Due to weight disruption of the ductwork the structure was spilt into two sections, front and back. The front section would be felled forward allowing an 87t excavator to shear the structure and the back section was to be skidded due to its vertical make up and off centre design.
For the front section of ductwork simulation engineering was used to predict the fell scenario from pull to landing and vibration impacts. Temporary bracing was installed to support the structure and to prevent premature movement. Delta separated the front and back section of the ductwork and supporting steel, and placed specially designed cuts throughout the structure. A pull cable was installed to the front of the structure and the front structure was felled in exact comparison to its simulation.
For the back section revolutionary engineered skids were designed and installed to the 75t each sections or structure. Transfer beams were bolted to the skids and welded to the support columns. Tow cables attached to the skids were attached to two 87t excavators. The support columns were cut below the transfer beams, freeing the structure from its concrete foundations. The two 87t excavators skidded the structure away from the Alinta area into an area where it could be safely felled and processed. The Boodarie Project was completed injury free.