Contracting joint venture Costain Skanska has reached a key milestone on the advanced works for Crossrail’s Bond Street station this week by completing the first two of five compensation shafts.
The works are to protect nearby properties from ground settlement during tunnelling works and box excavation for the new station.
Engineers have sunk shafts down to a depth of 17m using the jacked caisson method, whereby the shaft is constructed from the surface and pushed down into place. A steel or concrete cutting edge is placed followed by the first concrete ring. Hydraulic rams are used to sink the shaft 1m at a time, which allows another concrete ring to be added on top and the process then repeated.
Costain Skanska grout shaft engineer Lydia Walpole said the location of the grout shafts was “particularly complex” due to the restricted site at the heart of Mayfair, and the close proximity of neighbouring buildings. All five shafts are due for completion by the end of the year.