The Second Metropole Hotel Extension
In 1999 the Metropole built a further extension. The earlier one had had the problem of the Metropolitan Railway running only a few metres away from its basement wall. The new one had to straddle the live Bakerloo Line, North and South without interrupting the train services or endangering the passengers
Planning alone took fifteen months. With trains running every few minutes, there was great concern about the stability of the tunnels. Removing ground from above or to the sides, could have affected the circularity of the tunnels. As weight was removed from above, there would be a tendency for the tunnel to rise. Building the hotel above would add weight and might cause it to sink. By keeping these two in balance - carefully excavating and building in phases to keep the weights equal - the level of the tunnel was controlled. The foundation piles for the new hotel would be outside the tunnels but building them could also have affected the shape of the tunnels. This too had to be built into the equation.
The Basement Plan below shows the Bakerloo line passing below the centre of the building. Retaining piles surround the extension and the building stands on a mass of deep piles on either side of the railway. Throughout the process the tunnels were monitored electronically for both the circularity of the tunnels and for strain on the tunnel linings. These readings were transmitted electronically to both the Consultants at Canary Wharf and to the Laing Site Office at the Metropole Hotel. Any change outside permissible levels would have caused the trains to be stopped until the tunnels had been visually examined. This was never necessary and the passengers were safe throughout.