Steel Tubes
Aarsleff Signs On
Aarsleff Piling worked closely with civils contractor Costain installing an alternative tubular steel piled foundation support system for new sign and signal gantries on a section of the M62 motorway near Warrington, Cheshire. Aarsleff Piling drove clusters of long steel tubes into the embankment and central reservation in place of the bored cast in-situ reinforced concrete piles originally favoured to support the gantries.
Main contractor Costain constructed a new junction, junction 8, and widened the M62 between the new junction and junction 9 and carryied out other associated improvements, including the installation of new sign and signal gantries, on its £19.4M contract for the Highways Agency. The improvements were designed by the Highways Agency’s consulting engineers WS Atkins and included bored cast in-situ piles for the sign and signal gantry foundations. However in association with, consulting engineer Webber Associates, and Ove Arup, Costain suggested using steel tubes instead of the original concrete piled option. Costain adopted the steel alternative with Aarsleff Piling assisting in pile design.
Aarsleff’s approximate £170,000 sub-contract to Costain to supply, handle, pitch and drive 139 tubular steel piles was completed during four to five visits to the site. The company’s Banut 500 self-erecting fixed leader rig, equipped with a 5t hydraulic drop hammer, was ideally suited to the task as it was ready for work within just a few minutes of offloading from a low loader.
Aarsleff drove the tubes in clusters of 4 or 6 piles through approximately 6m of made ground into clay or granular glacial till and in the majority of cases to toe into rock. All the piles were 508mm diameter and varied between 7.8m and 20.5m long, with a number driven in two halves. When piles need to be extended Aarsleff initially drove the under piles, which could be up to a maximum 16m long, in each location. Costain then followed on behind butt-welding on the over piles before Aarsleff Piling returned to drive the extended tubes to full depth. After driving Costain cut off the tubes to level, and in-situ cast the reinforced concrete pile cap foundation.
Concerns over potential vibration and noise arising from the change from bored to driven piles were allayed by close monitoring and liaison with the local Environmental Health Officer. In the event all were satisfied that there is no cause for concern.
We installed all the piles and completed a gantry in a single shift when extensions were not required. We then finished off by testing the piles the next morning, this offered considerable advantages in terms of programme and confidence over a conventional bored pile which would require a minimum of 2 shifts to complete the works and a further 7 days before testing could be carried out. The fact that all piles are “pre-formed” gave greater confidence to the performance, integrity and quality of the piles.
Aarsleff Piling is able to offer its varied clients a comprehensive range of foundation project services, including design and installation of precast piles, steel sheet piles, steel bearing piles, timber piles, tubes and ground beams. Piles are installed using the company’s own extensive and modern fleet of self erecting fixed leader hydraulic piling rigs, including the largest in the UK capable of pitching and driving up to 32m long steel sections in a single piece.
