Saltwood tunnel in Kent lies just 15m below a cutting for the Channel Tunnel Rail Link now under construction. To ensure that rail traffic can continue during construction, Rail Link Engineering has installed monitoring equipment in the brick-lined tunnel.

Four of Leica Geosystem’s TCA2003 robotic land surveying units, calibrated to an accuracy of 1mm, survey 90 prisms embedded in the tunnel walls during a 15 min sweep every hour. Output from the Apswin Plus monitoring software is automatically compared to trigger values, and if a tolerance is passed an SMS message reporting the deformation is sent via the computer’s modem to a list of mobile phones.

Leica Geosystems, Switzerland

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