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No picnic in the park


ROGER BULLIVANT has used its Quiet Hammer to drive piles in the tranquil setting of St James's Park in central London.

Ground engineering for the Cake House project, a restaurant beside the lake, was not allowed to disturb park visitors or office workers in nearby Whitehall.

Designed to reduce noise levels when the hammer and anvil make contact, the Quiet Hammer drives piles into the ground at up to 12db less than a standard hammer.

'The damping mechanism is designed to suppress noise along with the associated perception of vibration, ' says Bullivant site engineer Matt Smith. 'In St James's Park it drove up to 35 piles a day into the underlying London Clay.' Bullivant, working for main contractor Ashe Construction, drove 105 precast concrete piles using its 5006-Q rig.

The 300mm diameter precast piles were 14m long, each comprising two, 4m long sections with a single reinforcing bar joined to a 6m long top section with a four bar reinforcing cage designed to accommodate lateral loadings.

Piles were installed at 900mm centres to support the reinforced concrete frame of the restaurant and finished off with pile caps.

Smith says the Quiet Hammer was preferred to CFA not just because of stringent noise controls, but because of restrictions on material deliveries.

'Deliveries were not allowed to be made between 10am and noon because of the changing of the guard at Horse Guards Parade.

'Bringing concrete to site would have caused added disruption to traffic and pedestrians around the Mall, ' he says. The lack of spoil produced by driven piles was an added advantage.

A test pile was installed before Bullivant's three-day contract and loaded up to three times working load to confirm the piles would accommodate the loads.

Pile caps and ground beams were cast by Ashe Construction.

A ground slab will be placed before the restaurant's concrete frame is erected.

The Cake House is being built for client the Royal Parks and will open next summer.

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