The Other Palace (St James Theatre)

A constrained site, requiring complicated engineering design at basement level

This site had two main in-ground constraints, a brick culverted sewer directly under the site and the future provision for Crossrail 2 tunnels at depth.

A theatre auditorium was proposed in the double-storey basement and therefore the basement footprint needed to be maximised. A permanent sheet piling solution was adopted for the basement walls with specialist installation techniques allowing the wall to be installed tight to the high-level culvert and the adjacent party walls.

The development site sat within the protected corridor for the future Crossrail 2 tunnels and therefore the foundation system and basement construction techniques had to be tailored accordingly. Deep load-bearing piles were not permitted and sheet piling lengths were restricted.

Below the basement Walsh developed a rafted solution, carrying out a ground movement assessment to see the effect of a range of possible tunnel alignments. The limited sheet pile embedment was overcome with a two level temporary propping system coordinated around the permanent works.

To accommodate the eight-story residential element, all being transferred at first floor level. We used long-span post-tensioned concrete beams creating column-free theatre space. Deep beams were incorporated into the walls of the theatre to bridge the superstructure over the sewer.