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Action station

Bam Nuttall is working to deliver a new lifeboat station for the Royal National Lifeboat Institution’s Lizard crew in Cornwall. Paul Thompson reports.

On the remote Lizard peninsula at the southern tip of Cornwall, contractor Bam Nuttall is building a new £7.5M lifeboat station for the Royal National Lifeboat Institution (RNLI). When complete it will house the latest “Tamar” class of lifeboat.

Access to the site is difficult as it is located at the foot of a 45m cliff which can only be reached by a single track lane.

Jack up barge

An 18m by 30m jack-up barge was used as a platform to carry out most of the work in the sea. Getting access for the land work was trickier. A local farmer let the team use his barn as a stock-holding point and materials had to be ferried to site on his tractor-borne trailer.

“We started the enabling works in May last year - streams were culverted and a small bridge strengthened so that it could carry some of the loads,” says Bam Nuttall site agent Lloyd Wickens.

The new station is shoe-horned into the cove with barely 1m separating the sides of the reinforced concrete slab that will become the station’s boat deck and the granite and schist walls.

“It wasn’t feasible to carry out large pours because of their complexity”

Lloyd Wickens, Bam Nuttall

The project uses the existing concrete slab and buttress by adding newly built extensions on either side.

“The existing wing wall is mass concrete around 1m thick. Tests were carried out on this concrete in 2008 and it was found that it was still in excellent structural condition,” says Royal Haskoning project manager Jonathon Kirkland.

“We assessed the capacity of the sample cores we took and found that they were very strong under axial loads but the lack of any steel reinforcement meant there was no performance against shear.”

Shear wall

To combat this the team has installed a shear wall at the front of the slab. This is fixed into the base of the cliff. A series of rib beams has also been cast into the buttress and a layer of compressible fill separates the original slab from the new 650mm thick slab which is heavily reinforced with steel reinforcement of up to 32mm diameter. Essentially the installation forms a sandwich of compressible fill between the new and the existing slab. This ensures boat winching loads and wind and wave shear loads are not transferred into the existing slab but through the new deck and into the newly placed piles.

“We used standard C40/50 concrete, supplied by Bardon Concrete at Redruth, for all the deck pours,” says Wickens. “It wasn’t feasible to carry out large pours because of their complexity thanks to the ribs, wing walls and buttress. There were no additions to it though, not even during the cold winter,” he adds.

Twenty seven 762mm diameter tubular steel piles have been installed, three to help support the new section of slab and 12 pairs to help support the slipway which falls toward the sea at a gradient of one in eight.

Hollow piles

These 20mm thick hollow section piles, installed by Bam Nuttall’s drilling arm Bam Ritchies using its down-the-hole hammer, are grouted from the bottom up at up to 10m depths.

Precast concrete transoms span the tops of the piles to form the base for the galvanised steel grillage slipway.

These are manufactured by local precaster Cornish Concrete, which used lightweight aggregate to combat any reach issues during placement.

The transoms, galvanised steel slipway and piles were all delivered to the jack-up barge from Falmouth. The lower sections did need the attention of a dive team to install.

Now with work on the slipway complete the Bam Nuttall site team is concentrating on building up the boathouse structure.

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