Design and construction of a hand mined Tunnel

Summary

A link passage between Crossrail’s Bond Street station and London Underground’s Bond Street station was constructed to allow pedestrian access between the two. To enable this, an existing ventilation tunnel from the Central line needed to be diverted.

The preliminary design was carried out by the LU Station upgrade team; however, due to programme requirements the detailed design and construction of the works were undertaken by Crossrail. The work was programme critical to the opening of the Crossrail Station and therefore had to be met within a set timeframe.
The design and construction of this diversion had many obstacles to overcome. Building a safe solution in a confined area required input from the Contractor at an early stage. The final solution had to be optimised to limit ground movements on various assets in the Bond Street area. This meant minimising the size of the launch chamber, constructing the 2.4m ID diversion tunnel using SGI rings on a tight alignment beneath existing structures and using traditional hand mining techniques to minimise excavation profile. Each of these design optimisations in turn generated significant challenges during the construction.

Issues encountered on site included, amongst others, the construction of an independent ring to achieve the alignment and excavation through an over-sprayed SCL lining. Further challenges were also encountered in the project to ensure the final asset would meet both Crossrail and LU standards. These included access arrangements, airflow requirements, waterproofing details and its connections to existing structures.

The tunnel has now been built and this paper covers the design and construction which enabled this challenging project to take place.