The Jubilee Line Extension project lengthened the London Underground line through South and East London from Green Park Station to Stratford Station. Westminster Station was one of the newly built stations and involved the construction of a 38m deep excavation and two station tunnels in close proximity to the Big Ben Clock Tower.
GCG was appointed Specialist Geotechnical Advisor for the Jubilee Line Extension project, responsible for evaluating site investigation methodologies, reviewing geotechnical design matters and providing specialist expertise during construction.
For the Westminster Station specifically, GCG undertook a series of soil-structure interaction analyses relating to the construction of the station to assess the effects of this work on the Big Ben Clock Tower and devise measures to mitigate its effects. While excavation to form the station box was underway, additional analyses were carried out to assess the implications of changes to the construction sequence (grouting, propping, etc) and to assess the need for grouting beneath the clock tower to compensate for movement resulting from construction. These assessments had a direct influence on the protection works and on the methods of construction that the Contractor was able to adopt for this major and very sensitive part of the Jubilee Line.
GCG was also retained by London Underground Ltd’s project team to assess the measured movements of the clock tower and the surrounding ground. From these assessments the form of mitigation measures (compensation grouting, a technique introduced to the UK by GCG) was directed. Comparisons between the measurements and movements of the retaining walls showed good agreement; the results of these comparisons have been published in a number of technical publications.
Higgins, K. G., Potts, D. M. & Mair, R. J. (1996). Numerical modelling of the influence of the Westminster Station excavation on the Big Ben clock tower. Proc. Of the Int. Symp. On Geotechnical Aspects of Underground Construction in Soft Ground, London, Balkema, pp.525-530
Higgins, K. G., Kovacevic, N. & Potts, D. M. (1999). Use of appropriate soil models in soil-structure interaction analyses. Proc. Of the 2nd Int. Symp. On Pre-failure Deformation Charactersitics of Geomaterials, IS Torino ’99, Vol. 1, Turin, Italy, pp.773-781