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1. Index
2. CMCS at BRE
3. Development of AMS
4. Non-destructive testing of Marine Jetties
5. Fixed sensor monitoring of Diaphragm walls
6. Monitoring Buildings during Redevelopment
7. Tunnel Monitoring
8. Embankment Systems
9. Loggers
10. Tunnel Distortion Monitoring
11. In-place tilt monitoring system
12. Tunnels Interaction System
13. Re-Development of Small Properties
14. Viaducts
15. DLR at Mansion House
16. Tunnel Monitoring System (Discrete beams)
17. CTRL 240
18. Dams
19. Electro-levels
20. Movement indicators
21. Results of Charing Cross Load Cells
22. Non-destructive testing of concrete structures
23. Radio in Construction Monitoring
24. Settlement Reducing Piles
25. Land Surveying and Total Station Monitoring
26. Vibration Monitoring
27. Monitoring the complete strain history of concrete elements
28. Past CMCS Projects

The Severn Railway Tunnel (risk management)

The monitoring system installed in the 150-year-old Severn Railway Tunnel is used as an example of the sensitivity and stability needed to give the engineers responsible for managing risk confidence in the monitoring system. The safety of trains passing through the tunnel while the Second Severn Crossing was constructed was the major concern. The centre foundation for the new Second Crossing suspension bridge straddled the tunnel close to mid-channel of the Severn Estuary; the closest piles were only 5m away from the tunnel lining. As illustrated in the diagram electro-levels, reading to one arc second resolution, were fitted in the brick lining of the Severn Railway Tunnel to monitor any distortion of the brick lining during installation and loading of the piled foundations.

The two graphs are from one of the electro-levels, the top graph, on a scale of +/- 5 arc seconds shows two cycles of movement a day corresponding to the tidal movements in the sea 30 m above the tunnel. Over the seasons the size of the cycles changed with the level of tide. The bottom graph (on a scale of +/-300 arc seconds) shows a typical yearly cycle of movements in the lining of about 100 arc seconds.
During critical stages of construction daily trends in the data were closely monitored to ensure there was no adverse effect on the lining as a result of the piling. On a 5 arc second scale any significant distortion of the tunnel lining due to the pile construction would have been detected immediately by the electro levels. On completion of the project, 44,000 hours later, the outside Parties Engineer wrote the following:

'I should like to take this opportunity to thank you for your co operation throughout the construction of the Crossing, in developing and maintaining efficient and successful monitoring systems. These have given British Rail and Railtrack the confidence in knowing that any minor changes in behavioural patterns of the tunnel fabric could be detected and appropriate action taken'.

The Kingsway Tunnel (risk management)

Recent concerns about fire risks in tunnels and adequacy of escape routes has caused Liverpool authorities to link the two bores of the Kingsway tunnel by three cross passages. The safety of road traffic passing under the Mersey River while the work was carried out was to be ensured.

Electro level beam monitors were installed in both of the nine metre diameter main tunnels to observe any distortion as accesses were cut out for the cross passages. The electro levels (read at one arc second resolution) were fitted to the main tunnel lining on 2m beams at the entrance and exit locations for the cross passages, as shown on the NCE photograph (right).

The small cyclic distortions of the main tunnels due to tidal changes in the Mersey 30 m above were clearly monitored by the electro levels. Observing these small movements gave the on site engineers confidence that the monitoring system was operational and would detect any additional distortion of the main road tunnels during the mining operation.

The display software (previous page) gives the site engineer an over view of all the instruments, see the example above. The graph (above) shows results from one of the electro levels indicating the typical two cycles a day tidal effect on the tunnel. If pre set threshold levels of movement in any location are exceeded the location on the display changes colour to warn the engineer visually that the level has been exceeded. Plots of any instrument between selected time intervals can be displayed to show trends in the movements being recorded. To make the system more fail safe it is also fitted with an automatic 'alarm dial out unit' that informs responsible personnel of threshold levels being exceeded via their mobile phones. Text messages can be sent within seconds of levels being exceeded. Data from the system can also be posted on a Web site if required for more general dissemination of the data.