Piling commences on the deepest basement…..
Set to be the deepest basement under construction in London this year, the new development in London’s West End is being constructed next to Bond Street Station’s South bound Jubilee Line platform and over a Royal Mail Tunnel.
‘Mail Rail’ is a 2 ft (610mm) gauge narrow driverless underground railway built by the Post Office in 1927 and remained operational until 2003.
The engineering of the 4-storey 18 metre deep basement required various detailed ground movements assessments to investigate the likely effects on the tunnels as well as adjacent buildings and infra-structure. The basement is founded on 1200mm thick raft foundations, within a secant piled basement wall designed with an integral reinforced concrete lining wall. Assessing ground movements is complex and many factors including soil-structure interaction effects as well as the stiffness of propping systems that influence movements were assessed.
Logistics and adopting the right construction methodology are crucial on such small confined sites and various approaches were considered early on such as ‘hybrid top-down’ and the use of ‘dough-nut slabs’.
With a number of key stakeholders to satisfy, Manhire Associates were able to develop detailed proposals and technical submissions without the benefit of a ground investigation by considering a range of soil parameters based upon historical data. The Ground Investigation was undertaken later to effectively verify soil parameters chosen in the original analyses and for the pile design.
Cementation Skanska chose 1000mm diameter cased secant piles (CSP) and piling is now well underway.
We look forward to seeing the excavation extend deeper and deeper over the coming months.