Groundworks specialist Mabey Hire has just completed its largest ever excavation support project, delivering 450 tonnes of its proprietary waling beam and propping equipment, to be installed on five levels into a 9,000 cubic metre excavation. The excavation forms part of the £145M Derby Derbyshire Waste Treatment Centre being built at Sinfin, Derbyshire, and measures 39 metres long, over 19 metres wide and, at 12 metres deep, also represents Mabey Hire's deepest ever excavation support project. When the facility is completed in 2017, the centre will accept waste into this large reception pit, where it will be held before being sorted, processed and used to generate power for 14,000 homes.
The pit was constructed using the cofferdam technique of sinking sheet piles into the ground before beginning excavation, and this process was planned by Interserve construction with Mabey Hire engineers working collaboratively. The pit was excavated by Clumber Civil Engineering as Mabey Hire began to install a combination of Super Shaftbrace and Supershaft Plus waling beams and Super Bracing 400 and 600 struts. The Mabey Hire waling beam and propping solution was able to provide greater working room within the excavation thanks to the Super Bracing Struts which can be used to create unsupported spans of up to 31 metres. The choice of a sheet piled cofferdam solution, supported by as few frames as possible was the most economical and sustainable solution available, as the equipment has been removed and will be reused elsewhere, in contrast to a fabricated steel frame solution or other secant/pile walling method.
In total, Mabey Hire supplied 450 tonnes of equipment to support the excavation – the largest amount it has ever supplied to a single project. Every frame was colour coded and every component numbered to ensure the teams installing them knew exactly where on site they were required. In order to maximise efficiency and minimise environmental impact, every delivery of equipment was precisely timed to fit with crane availability, and the equipment was single handled straight into the excavation.
Mabey Hire's excavation support scheme, and involvement in the design and planning process, yielded further advantages after the excavation was complete and it was time to pour the concrete pit base. The design of Mabey Hire's system allowed the three lower frames to be removed after the base had been cast, allowing complete freedom from obstructions at the working level. Mabey Hire also created a complete building information modelling (BIM) model of the excavation support system using its in-house Revit library of components, even though there was no mandatory requirement for the works to be BIM compliant. This allowed teams to preview the complex installation and removal sequence of support frames around the excavation, concrete construction and backfill operations, and identify any possible problems before they became reality.
Mabey Hire's project sequencing drawings were printed out on large laminated sheets and posted around the excavation perimeter which aided the health and safety of the scheme, ensuring all site operatives were aware of the sequence, design and purpose of the whole project. The drawings also served to highlight construction constraints, and stimulated constructive engagement with all levels of the site team.
The Derby and Derbyshire Waste Treatment Centre is scheduled to be completed in April 2017 and, when operational, will significantly increase Derbyshire and Derby Councils' recycling rates, and reduce the amount that both councils send to landfill.
View the time-lapse installation video here.
Engineers from Mabey Hire worked closely with Interserve's temporary works team to the benefit of the whole project, as Rhys Jones, Interserve's constructability manager explained,
“There was a collaborative approach from the outset between Mabey Hire's engineers and our technical services department. This allowed Mabey Hire to fully understand the project requirements, which led to a more economical outcome during the detailed design phase.”
