CONTRACTORS ARE reducing the number of columns in Unilever's new headquarters building in London by transferring loads to 14 concrete caissons.
These are arranged in clusters and will support cores which will enhance the building's load bearing capacity.
The enormous caissons, made of 600mm deep, 2.74m diameter precast concrete rings, are being jacked 20m into the ground from a fabricated steel reaction frame.
Ground conditions feature water-bearing sand, gravels and soft clays above London Clay.
Groups of four concrete caissons in the south west, north east and north west of the site are being filled with concrete and pile capped.
Three 10-storey concrete cores rest on the caisson clusters, giving the building lateral strength.
The three cores will reduce the need for internal columns in the refurbished building, increasing floor space.
Meanwhile, 1,800 of the building's original 1930s concrete-filled, step-taper steel shell Raymond piles will remain to underpin the building and carry some vertical loads.
The existing piles will be re-used because Unilever has retained detailed records of their positions.
The Grade II listed art deco stone façade will form the exterior of a new headquarters for Unilever overlooking the Thames at Blackfriars Bridge.
Foundations contractor is McGhee Construction, main contractor is Bovis and Arup is structural engineer and foundations consultant.