London Underground Limited’s (LUL) Foundation Network of step free access (SFA) schemes was aimed at making Underground stations accessible to mobility impaired customers. Due to its town centre location and its function as an important bus/Underground interchange, Archway Station was included in this Foundation Network. Step free access to platform level at Archway Station was proposed via a circular vertical lift shaft from ticket hall level (upper SFA lift shaft) to an intermediate level passageway (4.4 m internal diameter tunnel) and a rectangular vertical shaft from the intermediate level to the platform level (lower SFA lift shaft). Furthermore, the SFA scheme included an inclined link staircase for staff access and emergency means of escape.
GCG were commissioned to advise on the ground investigation and the associated laboratory and field testing. Additionally the scope of works included undertaking a series of analyses of the scheme to aid in its design and assess effects of construction on existing surface structures and sub-surface infrastructure.
The potential for damage to surface structures arising from construction was assessed using GCG’s in-house Tunnel & Box Settlement Estimation Program (TuBoSEP) which was developed based on GCG’s vast experience in the field of building damage assessments. To assess the effects of construction on the existing sub-surface infrastructure, GCG carried out a series of 2D and 3D finite element (FE) analyses using their in-house FE code ICFEP. The most critical aspects of the SFA scheme were intersections between new and existing infrastructure. For example, in order to construct the lower SFA shaft, it was necessary to remove large sections of the existing platform tunnel linings. GCG analysed this aspect of the works using 3D FE analyses.
Harris, D. I. & Franzius, J. N. (2005). Settlement assessment for running tunnels – a generic approach. Proc. Int. Symp. of Geotech. Aspects of Underground Construction in Soft Ground, Amsterdam, 225-230