Pall Mall

A Challenging Piling Regime

A very thorough piling regime across the site involved the installation of a contiguous piled wall on three sides of the basement, stretching to a depth of 25 m through deep gravels and underlying London Clays which featured under the site. Bored temporary cased piles were installed to hold the significant surcharge loads from the existing buildings surrounding the works. Great sensitivity was required throughout the works and we were able to minimize the impact of the augering process on the surrounding listed buildings by using bored temporary cased piles.  

Access and headroom limitations of 5.5m beneath flying shores meant that we opted to pile the walls from basement level and then excavate down to sub-basement level.

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Post Tensioning

The concrete superstructure was sprung from the capped contiguous piles at basement level, and featured post-tensioned concrete slabs to lighten the load on the foundations. Post-tensioning techniques also meant the client was able to achieve very slender slabs of 270 mm thickness as well as the 12 m spans with no internal columns, which optimized the internal office space.

Brickwork Arches ‍

The rear of the new building featured a glass roofed stairwell and three storey atrium which required some complex brickwork to achieve the client’s complicated design involving a series of brickwork arches and semi arches. In places some of the bricks in that façade are only half a brick thick. The original design had planned a series of prefabricated steel goal post supports, but the site was too confined. Geostructural Solutions were able to develop an alternative system of sacrificial propped cast in situ concrete, which worked very successfully.

Timbrel Arch Feature Cellar  

The Brickwork design from the atrium was incorporated into the basement which featured a new brick-tiled vaulted timbrel arch cellar. This became part of a new hospitality suite and wine school. Set at the sub-basement and basement levels and with a plan area of around 20 m by 12 m, this two-story suite featured an elliptical viewing well alongside the timbrel brick vaulted ceiling, running through the centre of the reinforced concrete slab that creates the new basement floor.