No. 1 Poultry

This prestigious but controversial development in the City of London involved the demolition of a Grade 1 listed structure. The site effectively represents an island, being isolated by roads and a number of London Underground (LU) tunnels, typically 2 to 3m from the perimeter of the site. Two LU Central Line tunnels lie to the North while three LU Waterloo & City Line tunnels are present to the South. All of these tunnels converge at Bank underground station which is just to the east of the Site.

The LUL tunnels were constructed over one hundred years ago with cast iron segmental linings. The tunnels themselves are sensitive to distortions, as is the machinery inside the tunnels, such as the pedestrian “Trav-o-lator” or moving walkway contained within one of the LUL Waterloo & City Line tunnels.

GCG were retained by LUL to examine the short-term and long-term effects of construction on the tunnels and installations within them using advanced numerical methods. Initially, however, it was important to undertake a detailed review of the ground conditions (fill, sands and gravels overlying London Clay Formation and the Lambeth Group) examining the data from the site investigation and supplementing it with information from other sites in the vicinity. The detailed numerical analysis mimicked the historic development of the site and construction of the new structure. The most critical conditions were identified by modelling the construction sequence with the stage-by-stage deepening of the basements. Based on this analysis, a further suite of analyses were undertaken to predict the longitudinal profile of the Trav-o-lator during construction. This allowed an assessment to be made of the effects of the development on the continued operation of the Trav-o-lator.