WHAT ARE thought to be the longest tubular steel piles to be driven in the UK have been installed as part of the £94M Cardiff Bay barrage project in South Wales.
Aarsleff Piling, the UK subsidiary of Danish Contractor Per Aarsleff drove the 610mm diameter up to 33m long piles in single lengths using a leader rig. The piles were installed vertically and with a rake of 1 and 4 through up to 32m of fill, clay and into underlying mudstone for the sluice training wall, which channels water into the barrage locks.
Aarsleff carried out the work for barrage main joint venture contractor Balfour Beatty/ Costain, using an in-house designed rig based on a Hitachi KH180-3GLS hydraulic crawler crane. The rig weighs 66t and has a 38m high mast, which allowed it to drive the up to 33m long, 9t piles. It was fitted with an ICE 815 hydraulic vibrator and Junttan HHK9a hydraulic piling hammer.
The vibrator was used to initially toe in the 42 piles in the correct position and pitch and then the Junttan hammer completed the drive. All the piles were driven to a toe depth of 23m below Ordnance datum as specified by project design engineer Sir Alexander Gibb & Partners for client Cardiff Bay Development Corporation.
The Junttan hammer hydraulically accelerated the 9t ram weight during the fall, boosting the impact energy and increasing the efficiency by up to 20% over a conventional free fall hammer of the same weight.