Elephant and Castle Town Centre Development - Engineering Within the Harwich Formation

The excavation for the new ticket hall is above London Underground Ltd’s (LUL) Bakerloo Line tunnels and comprises up to ~18m of excavation to form the basement and associated transfer beams of the eastern half of the new Integrated Ticket Hall.  The Harwich Formation layer is approximately 8m below the general basement formation level (and hence ~5m below the transfer beam trench formation) and is known to be water bearing due to its coarse-grained nature and, therefore, of relatively high permeability. The project team had to assess the basement formation stability in this area, which is founded within the London Clay but is subject to the hydrostatic uplift pressures from the Harwich Formation below. Any technical solution had to also consider the difficult site logistics.  Our project team faced the formidable challenge of constructing a new integrated ticket hall (ITH) for the Elephant and Castle Town Centre development. This complex engineering feat involved creating deep transfer beams to support the structure, directly above the century-old Bakerloo Line tunnels. The key innovation was our approach to managing the high hydraulic conductivity of the Harwich Formation, a critical geological layer. Collaboration was paramount. We collaborated closely with the Engineer WSP, tunnel owner TfL, and other stakeholders to design and implement a solution.