This time lapse video shows the construction of a grout shaft in Dering Yard.
The grout shaft was sunk to a depth of 17m. It is one five shafts required to ensure that nearby properties are protected from ground settlement (small movements of the ground) during our tunnelling works for the new Crossrail Bond Street station platforms.
All the work within Dering Yard was performed through the Medici passage, a narrow vehicle width passage with restricted height from New Bond Street. Access to several properties and emergency fire escape routes, as well as a public right of way, had to be maintained through this passage at all times while this work was carried out.
Crossrail's contractor Costain Skanska Joint Venture (CSJV) built the shaft structure using a "top down" method of construction, whereby the shaft is constructed from the surface and pushed down into place.
As you can see form the video above, a steel cutting edge is placed at ground level and the first concrete ring is then installed on top of the cutting edge. Excavation of the ground within the shaft is combined with the weight of each of the concrete rings and the pushing force from hydraulic rams.
The hydraulic rams are used to sink the shaft one metre at a time, allowing another concrete ring to be placed and the process to be repeated. The hydraulic rams are used to ensure the vertical sinking of the shaft. The crane is used for personnel, materials, equipment and removal of excavated material.
The next stage of work is to install small-diameter underground pipes, known as Tube A'Manchettes (TAMS), in an array from the base of the shaft. When the grout shaft is in operation, a cement-like material, called grout, will be injected via the TAMS to stabilise the ground beneath the buildings.
Similar shafts are being constructed in Tenterden Street, Haunch of Venison Yard, Davies Mews and South Molton Lane.
Further information about ground settlement and Crossrail's approach to protecting buildings can be found on our ground settlement page.