The multi-storey car park in Osborn Road, Fareham, constructed in 1970, using lift slab construction has presented its challenges over the course of the demolition project for HWM Group. All were foreseen, scrupulously identified and mitigated through modelling and calculation scenarios with specialist engineers.
Demolishing multi-storey car parks constructed using the lift slab method presents unique challenges compared to traditional construction techniques. Lift slab construction involves assembling precast concrete panels on the ground, then lifting them into place using hydraulic jacks onto columns to create the building's structure. While this method offers efficiency during construction, it introduces weakness and instability complexities during demolition.
Here are some key challenges:
Structural Integrity: Lift slab structures rely on the interconnection of precast panels and temporary supports during construction. The concrete is generally heavily reinforced with rebar. Demolishing these structures requires careful planning to maintain structural integrity and prevent premature and uncontrolled collapse. Disassembling the lift slab components including the support columns in the correct sequence is essential to avoid compromising the stability of the remaining structure. Normally, the strongest part of the building is located in the middle, however, with the Fareham MCP the strongest points were located in other areas such as lift shafts and stairwells located at the side of the building, leaving the weaker points more vulnerable as demolition got under way.
Noise and Disruption: Demolition of multi-storey car parks generates significant noise, vibration and dust impacting surrounding businesses, residences, and public spaces. Behind the Fareham car park is a large shopping centre with retail unit delivery access via a service road at the side of the demolition site. There is a well-used public library and a construction site adjacent to the multi-storey demolition site, together with access roads and residential properties opposite.
HWM Group’s planned approach was to enter from the front of the car park facing the main road and demolish column sections from the inside-out in a horseshoe shape. Using pulveriser attachments with rebar cutters and a Komatsu PC390 high reach excavator, the concrete slabs were effectively ‘munched’ away from the columns in sections to ensure that the perimeter walls of the car park remained sturdy during the works. This approach had the additional benefits of containing and reducing both dust and noise emanating from the site.
Debris & Environmental Impact Management: Lift slab construction produces large quantities of concrete debris, precast components and metals that require careful handling and disposal. Efficient debris management strategies, such as crushing on-site and repurposing concrete aggregates were used along with our own waste handling division for scrap metals, wiring and plastics. Around 97% of all materials were recycled.
Repurposing the concrete materials and segregating hazardous waste helped minimise disposal costs and significantly reduced the environmental impact of more vehicle movements to and from the site.
Demolition activities on this scale can’t escape the release of dust, debris, and pollutants into the air and whilst contained within the outer structure for most of the demolition, effective dust suppression measures were deployed throughout to further reduce the impact on business users, shoppers and local residents.
Summary: In navigating these challenges, HWM Group worked closely with Fareham Borough Council and their client Neilcott Construction collaborating in the planning and strict adherence to safety and environmental regulations. Demolition teams must collaborate closely with engineers, environmental consultants, and regulatory agencies to ensure the safe and successful demolition of multi-storey car parks constructed using the lift slab method.
HWM Group Director, Adam Blake, said, “The decommissioning approach taken by HWM Group for this multi-storey car park demolition stands as testament to HWM Group's expertise, commitment to sustainability and dedication to minimising the impact on the local community. As Fareham town centre undergoes transformation, this project sets a benchmark for responsible and efficient urban decommissioning of lift slab multi-storey car parks and the safe future development to enhance public spaces and services for the future.”