A NEW concrete slab has been cast on top of piles driven through a Manchester road that was at risk of collapse into voids below.
Foundation contractor Aarsleff Piling won the contract to prop and support the slab for a 20m wide access road to the Royce Trading Estate next to the Trafford Park shopping complex.
Working for main civil engineering contractor Birse, Aarsleff installed precast concrete piles driven through holes cut through the old slab.
After driving, the piles were sawn off to the same level to act as simple props and support the new slab resting on top.
Built on the site of a factory containing asbestos, the road originally sat on a series of transverse brick walls about 2m apart, over ground containing voids ranging from 300mm to more than 2m deep.
To protect against the small risk of contamination from any asbestos residue in the voids, the piling team wore protective clothing and masks.
This safeguard was supported by Birse, which employed asbestos survey and removal firm Winsulate to constantly check and monitor for the presence of asbestos during the project.
TGA Building Consultancy was appointed project manager, planning supervisor and party wall surveyor in 2003 to explore the various options for reconstruction. Aarsleff carried out test piling for Birse at the end of 2003, with consultant Clarkebond then designing the new road slab and its support structure.
Aarsleff carried out main piling in two separate phases. To keep access to the trading estate open throughout the project, Birse decided to work on each carriageway in turn.
Work started on site last September, with Birse cutting square holes in the 200mm thick road slab at the pile locations.
Aarsleff's team then moved in.
Its Banut 700 rig, running on loadspreading Navvy mats, installed the 300mm and 350mm square, fully reinforced, precast concrete piles with a maximum working load of 1100kN.
Aarsleff's subsidiary Centrum Pile made piles in lengths between 8.5m and 9.5m. Site workers drove these to refusal, about 6m, on a 6m by 3.5m grid through sandy clay to toe into the underlying sandstone.
Once piling for the first carriageway was finished, Aarsleff left site and Birse sawed off all the driven piles to the same level, before casting the new 300mm thick slab on top. The road simply rests on the piles, without any tying-in.
Aarsleff returned to complete similar piling for the second carriageway. Birse was due to finish last month.