Page 26 - W M Donald Newsletter - Edition Twelve

Effective construction and safety: the critical importance of temporary works
Scott Dickie is W M Donald’s Senior Technical Engineer. In this article, Scott explains why temporary works are fundamental to both the successful completion of projects and the safety of those working on them.
During summer 2020, W M Donald completed a major project at RAF Lossiemouth which included the installation of seven large interceptor tanks up to 30m long. Sheet piles were driven into the ground using an excavator mounted Movax side clutch vibrating hammer to create a cofferdam. The top waler brace was installed just below ground level and the inside of the cofferdam excavated to a depth of 7m. A second waler brace was installed at an intermediate depth and finally a concrete plug was poured once the cofferdam had been excavated to the required depth. The concrete plug seals off the bottom of the excavation and holds the toe of the piles. The tanks were lowered and secured in position on the concrete plug using tie down straps. The entire cofferdam was then flooded with concrete and the tanks ballasted with water at the same time to prevent flotation and crushing of tank walls.
More recently, W M Donald installed an IDS package pumping station at Ness Side for Tulloch Homes. The ground conditions comprised rounded cobbles (shingle). A 7m deep excavation was required and the cofferdam was created using sheet piles and waler frames.
The waler frame and sheet piling used to create the cofferdams on these projects are known as ‘temporary works’. The specification of equipment and the installation process to construct a cofferdam is known as the ‘temporary works design’.
Temporary works is a catch-all term for anything that isn’t permanent. BS5975:2019, the British Standard for temporary works, defines them as ‘...those parts of the works that allow or enable construction of, protect, support or provide access to, the permanent works and which might or might not remain in place at the completion of the works’. On W M Donald projects, temporary works are most likely to include earthworks (e.g. trench support), structures (e.g. concrete formwork), and special earthworks (e.g. crane platform).
Temporary works even include signage, temporary security fence support and site offices.
At W M Donald temporary works are first considered when quoting for a project. At this stage the significant elements of temporary works are identified and costed. On acceptance, the temporary works requirement is reviewed, and a design brief prepared for each element. A design for each element is subsequently developed, checked and signed off following an established process. Throughout the life of a project the temporary work elements are logged on the ‘temporary works register’ which is maintained and updated with additional temporary works elements identified as the project progresses.
Every W M Donald site has a Temporary Works Co-ordinator (TWC) responsible for managing temporary works and maintaining the temporary works register for their sites.
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