Synopsis
The construction of the Northern Ticket Hall (NTH) formed part of the overall redevelopment of London Underground's King's Cross/St Pancras station. A static tower crane was required to service the largely top down construction works. Due to the limited access and particular site constraints, the tower crane had to be located within the area to be excavated. To address the specific site requirements, an innovative foundation was developed comprising a single large diameter (2.1m) steel tubular mono-pile installed from the existing ground level and founded principally into the underlying London Clay. As the steel tube would be eventually exposed down to the underside of the ticket hall base slab, the pile was designed as a free-standing cantilever with limited allowable movements that would meet the crane's safe operating requirements. This paper describes the geotechnical and structural design challenges of an unusual tower crane foundation, as well as the particular construction and operational requirements.