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Lifeboat station braced for stormy weather

DEW CONSTRUCTION had to cope with gale force winds, a 10m tidal range, the stormy Irish Sea and difficult ground conditions while building a new lifeboat station on the Cumbrian coast.

The Royal National Lifeboat Institution's station at Roa Island, near Barrow-in-Furness, had to be replaced to accommodate a new generation of lifeboats.

Dew Construction's £3M contract for the RNLI involved building not only the station, but a 110m long elevated walkway and a 75m long slipway with its toe permanently under water.

The original plan was to use cast insitu pad foundations for the walkway but because of the difficulty of forming concrete between tides, Dew decided to partially precast the units on land. These were positioned on concrete blinding using a crawler crane, with reinforcement and shuttering fixed and the infill sections concreted.

Driven tubular piles support the slipway, driven into the seabed and cut off to form the 5.5degrees slope. Toe construction was carried out in a sheet pile cofferdam infilled with mass concrete and included a steel keelway providing the interface between the slipway and the seabed. A temporary 'half tide' cofferdam provided access to the permanent cofferdam.

All piling and crane work was carried out from a temporary stone causeway parallel to the main structure but even so, the 10m tidal range meant progress had to bow to the tides.

The 700sq m lifeboat station stands 10m above the foreshore on an 800mm concrete slab mounted on 31, 750mm diameter concrete columns. During construction the slab was supported by temporary tubular piles, which were braced to prevent deflection.

The lifeboat station is now operational following launch tests at the end of last year.

Complex basement construction is nearly finished for the largest Marks & Spencer store in London.

Foundation contractor Bachy Soletanche had to pile through underground structures to form the deep basement and piled foundations for the new eightfloor building on a restricted corner site at Fenchurch Street in the centre of the City (Ground Engineering August 1999).

Although the previous building had been demolished before piling began, the 7m deep basement had to be left in the ground until the new, deeper basement structure had been built, because its two floor slabs acted as props for the surrounding streets.

This meant Bachy had to pile through slots cut in the slabs. The new basement is almost twice as deep and was formed by 304,31m long secant piles installed tight against the existing basement walls. Once in place, the two floor slabs could be removed.

The firm also installed 37,23m long,1800mm diameter bored concrete piles with steel plunge columns and 12,900mm diameter bored piles with 3m diameter under-reams for the steel frame of the new store.

Excavation for the deeper basements is now complete and new underground slabs have been constructed to provide M&S with four levels of underground storage and plant area. The exposed secant pile walls are being fronted with blockwork and the department store is due to open later this year.

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