TAYLOR WOODROW Foundation Engineering has just finished a major hard/hard secant piled wall at County Hall, London, the former home of the Greater London Council, on the banks of the River Thames.
The wall was built to provide struct- ural support before excavation of the basement for a residential development adjacent to Belvedere Road, sandwiched between the two halves of the County Hall buildings.
Client was Galliard Homes, with Costain Construction as main contractor. Whitby & Bird developed the conceptual design, with Clark Smith Partnership and Campbell Reith Hill progressing the design through to construction.
The site posed a number of technical problems. The geometry of the 170m long, 40m wide and up to 10m deep excavation is split level and, because the site sits close to the river, the water table is very high, affecting the lowest sections. The difficult ground was compounded by obstructions, including a low-level BT duct the length of the site.
Taylor Woodrow was respon- sible for the design and construct- ion of the secant pile wall and the temporary works. It designed the male piles to do all the structural work, removing the need for reinforcement in the female piles which, it claims, made the scheme more efficient and cost effective.
And the company also devised a temporary propping scheme that allowed the high level side of the excavation to be temporarily propped from the low level side by a system of raking shores carefully positioned to minimise the forces induced in the wall.