Crossrail C421

Project summary

Service provided:  Tunnel Deformation monitoring during adjacent construction works
Location:  London, United Kingdom
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Client:  Balfour Beatty / Morgan Sindall / VINCI Construction JV
Period of the service:  2004
Duration of service:  3 Months


British Telecom tunnel monitoring

To assist with the development of the Crossrail project, Crossrail Limited (CRL) required the establishment of monitoring schemes to assets during construction works.


In order to monitor the movement of the BT cable tunnel, due to works carried out by BBMV for the Crossrail C421 Western Ticket Hall project at Tottenham Court Road Station, a combined manual and real-time monitoring system was installed.


The BT tunnel runs North to South adjacent to the Crossrail site at Dean Street. Dean Street was developed between 1677 and 1697, extensively rebuilt in 1734 and some of the buildings in the area fall within Soho Conservation Area.


For this contract, monitoring equipment was established in the section of the tunnel lying within the 1mm settlement contour. The following was installed by Sixense:


  • Tiltmeters and Electrolevel beams on the tunnel lining (automatic monitoring).


  • Prisms and level points in the tunnel invert and crown (for manual survey).


In order to safeguard the tunnel at specific phases of the foundation works, daily manual survey readings were taken by carrying out a full traverse on local grid. All instrumentation was installed by clamping to keep the number of intrusive fixings to a minimum.


Many proposed over site developments are in progress or planned for this area where the construction works for Crossrail line are due for completion in 2017.

Project Key figures

70 Tiltmeters
52 Prism Targets (Manual)
28 Precise Level Points

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