A NOVEL approach has been used to extend the basement foundation of an underground car park in Manchester, for what will be the largest Marks & Spencer store in the world.
On 15 June 1996, a 1.5t IRA bomb ripped through Manchester city centre. The extent of the damage to the old M&S store, which was close to the centre of the blast, was so great that the company decided to reconstruct its Manchester operation as a flagship store.
The new development will comprise 23,000m2 of retail space on four floors, with sub-basement car parking allowing direct access to the store. Bovis is management contractor for the job.
One of the first tasks was deepening the destroyed store's underground car park by another floor. Due to project programming constraints the walls of the car park had first to be extended downwards, enabling the basement floor level to be lowered, before the existing car park was demolished. Most of the excavation was in sandstone.
Bovis enlisted foundation and underpinning contractor Van Elle for its knowledge of restricted access geotechnical work, to devise a solution. Traditional excavation techniques would have been too slow and expensive, so the company suggested an innovative solution using a rotating rock cutter, fitted on a 35t excavator.
On site, the cutter proved efficient enough to cut two and a half weeks off the eight-week programme. Some 130m of wall has been excavated by up to 3.5m using the rock cutter.
The project was carried out in close liaison with the demolition contractors and casting of the concrete panels was done in a strict sequence to maintain the structure's stability.
Success has won Van Elle a further contract at the site, to build another 120m of 4m-deep diaphragm wall, using the same rock cutter. Managing director Robert Thompson says the development of the method has secured the company over £250,000 of work on this contract alone and there is a potential for more.
Van Elle is expected to finish by the end of May. The store itself is due to open in autumn 1999, when it will form the focal point of the £1bn Manchester Millennium rebuilding project.