Tunnel Lining and Track Bed Monitoring: Park Crescent

Challenge

Construction work at Park Crescent West lies partly above the Jubilee Line tunnels that run between Bond Street and Baker Street, and involved both demolition of existing buildings and construction of new ones. LU nominated Murphy Surveys to carry out comprehensive monitoring of the tunnel during the construction works, due to their reputation from previous successful projects. This required full 3D monitoring to understand potential deformation and settlement/heave movements associated with these works and was in conjunction with careful monthly manual monitoring. Line of sight issues meant that optical systems could not be used.

Murphy Surveys selected Senceive to provide a high precision and stable wireless monitoring system for tunnel deformation, convergence and longitudinal settlement/heave. As well as measuring track bed twist and cant. Ultimately this large-scale use of new technology would heavily rely on the combined efforts of LU, Murphy Surveys and Senceive.

Solution

Senceive already had huge experience in and around the main zone of influence on the Jubilee Line, having been responsible for the provision of the principal monitoring system for the award winning 3+ year BSBS (Bond Street-Baker Street) tunnel re-lining project. As a result, they were able to save money and effort by linking in to the existing communication backbone which extended to where the new monitoring started. The use of wireless tilt meters also helped fill in invisible areas and complimented the use of ATS for high precision laser monitoring.

167 wireless tilt meter nodes were installed in arrays of 5 nodes per ring using Senceive’s patented magnetic mountings at 10m centres over 335m of tunnel. 69 additional sensors were installed on track bed plates at 5m centres. In total 236 tilt nodes and 4 gateways were used.

Outcome

After many collaborative meetings between Murphy Surveys and LU to successfully integrate Senceive’s new technology into their comprehensive monitoring systems. The wireless nodes were installed on the tunnel lining to measure changes in the segment angle with sufficient precision to derive sub-1mm movements of the vertices in both horizontal and vertical directions. These were resolved in real time to generate net horizontal/vertical distortions of the tunnel sections.

Senceive worked with Murphy Surveys on the days of install and provided ongoing assistance through 1-2 year life of the project including routine support, network management and node replacement. Data was transmitted directly from the network of sensors to the existing Senceive BSBS Hub. The data was then easily integrated with the “Leica Approved” Geomos software interface with web-reporting, providing all the monitoring data within a single software web interface.