CMA Delta Group, in partnership with MB-Abbruchtechnik of Germany used computer modelling and custom built machinery to demolish a 140m high stack and boiler housings within the Verve Energy Kwinana Power Station, WA.
Scope of Work
First Part of the Kwinana Demolition
The stack was located inside the power station, which limited the demolition to a 100x70 metres area with a 50x60 metre exclusion zone around the base of the stack.
The design of the stack demolition was completed in house, and represents the only time this type of demolition has been completed in Australia.
To complete the project, CMA engineers designed a machine to demolish the stack from the top down. This was achieved in co-operation with the experienced German based company, MB-Abbruchtechnik.
The solution used was not only creative and innovative but also safer than explosives and reduced noise, dust and seismic disturbances.
The solution centred on a shear with a kibble slung from a tower crane attached to the side of the stack. The crane operator operated the shear which demolished the stack by taking bites from the top then dropping all debris into the kibble or down the centre of the stack.
This new technology enabled the stack to be demolished at a faster rate than normal, with zero impact to the power stations on-going operation.
Second Part of the Kwinana demolition
The second demolition Involved the removal of a housing structure containing redundant power station boilers K3 & K4. The demolition had to be completed within specific time constraints, area restrictions, and involved the removal of large amounts of friable asbestos scattered throughout the structure.
In accordance with CMA Delta Group policy, all of the asbestos in the structure was completely removed prior to the induced collapse taking place. To remove the asbestos the building was wrapped in plastic to ensure that no air borne asbestos particles could enter into the open atmosphere.
After the area was sealed off, those entering the "bubble zone" were equipped with respirators and a full body protective suit. By the end of the operation approximately 600 cubic metres of asbestos had been removed from the boiler house and surrounding area.
The Boiler House collapse was a partial demolition with the Boiler House being joined to the Turbine Hall Building. Verve requested that the Turbine Hall be retained for future use.
A temporary framework of columns and bracing was engineered to hold up the structure for the period of time before the drop.
CMA's structural engineers and experienced supervisors worked to develop a methodology for the drop, and to calculate the loads on the boiler house and the subsequent stress levels that each structural member would have to withstand.
Computer analysis was used to predict how the structure would behave in the initial stationary position and throughout the collapse. This type of analysis is the first of its kind to be undertaken in Australia.
After the design was completed the physical works began. Temporary footings were poured beneath the positions of the rear columns. These footings were completed early in the project to reduce the effect of settlements and soil consolidation.
Following this, the columns and cross braces were brought into the structure and welded in place. This required the coordination of some 20 tradesman working with boom lifts, cranes, excavators and under specific time restraints.
After the columns and cross braces were installed the new columns were raised to take the load of the boiler house and to remove any loading settlements in the footings.
On the 28th of February the final cuts were made and the structure was brought to the ground. This completed approximately 2 months of preparation work. Once the structure was in a stable position the customised demolition excavators processed the scrap and shipped approximately 3000 tons off site.
Site remediation included the removal of large volumes of contaminated soil from the site, which under-went further treatment before final disposal.
Throughout this process CMA worked closely with environmental engineers to ensure all remaining soil on the site was clean. The works consisted of removing footings under the boiler house and stack areas and excavation of the remaining site to a depth of 2.5m. This work was overseen by an on-site environmental engineer at all times.
Soil samples were continuously analysed for contaminates and removed from site for further treatment and replaced with clean soil. Following the removal of the contaminated soil the site was back filled and compacted to 95% Maximum Modified Dry Density (MMDD) with a 300mm thick layer of limestone used for the final finish.