FORESTS OF piles mark out the new road bridge across the River Tees at Stockton-on-Tees in Cleveland, installed recently by foundation contractor Aarsleff Piling.
The firm drove 84 steel H-section piles on each bank of the river in areas of just 27m by 7m for the abutments and approach embankments of the bridge. The structure forms an integral part of the £8. 9M South Stockton link road being built by main contractor Birse Construction.
Starting on the south bank, Aarsleff used one of its Banut 700 rigs equipped with a Banut 6t hydraulic free-falling drop hammer to drive the piles through soft to stiff clay into the underlying sandstone to achieve a set of 20mm with a 1m drop of the hammer.
Piles were installed in three rows of 11 for the bridge abutments. The first row, closest to the river, was driven at a rake of 1:4, the second at a rake of 1:8 and the third row vertically. A further 50 vertical piles form the approach embankment foundations behind.
The steel H piles, up to 24m long, were driven in two halves. After the first sections were pitched and partly driven, the upper sections were welded on and the piles driven to depth. An average of 14 half sections or seven complete piles were installed every day. Once piling on the south bank was finished, the rig was transported 20km around to the north bank, for a repeat operation.
Another contractor will install steel tube foundations for the bridge's central piers. Aarsleff installed a 914mm diameter steel tube test pile with an IHC S90 Hydrohammer on the north bank, which was later statically tested to 500t.
Pile testing firm Precision Monitoring & Control dynamically tested three piles on each bank to working loads of 4,000kN and 2,000kN, using a Banut 7t hammer to strike the test piles a day after driving.
Accelerometers and transducers on the piles were linked to a Pile Dynamics pile driving analyser which gave an instant readout of capacity.
The £170,000 piling contract took just eight weeks. Aarsleff is to return soon to install a 150m long line of steel sheet piling next to the south abutment.