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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

G Price & I F Wardle carried out field trials in the 1980s to compare the electro-level system with electrical resistance strain gauges to monitor the performance of laterally loaded piles.

The results from the tests are shown opposite and clearly demonstrate the ability of the EL system not only to monitor deflections but the data could be used to determine bending moments and soil reaction.

The EL system provided superior information on pile performance, and was also recoverable at the end of the tests (ref: Publication 24). Having proved their worth on simple structural elements it was then possible to use ELs with increased confidence to monitor the behaviour of more complex full-scale structures, which included diaphragm walls.

Sixteen electro-levels were placed at 2 m spacing in each of 4 inclinometer tubes (one per side) in the walls supporting the 30 m deep excavation. The graph opposite shows the monitored deflections recorded by the EL system installed in the North wall from 1988, through the summer and winter of 1991 to February 1998. The difference in temperature between the summer and winter in the UK is about 30 degrees C, which caused the top floor slab (of the top down construction) to expand and push the wall outwards in the summer by about 4 mm, which the sensitive EL system could easily detect. The reverse curvatures seen in the plots are at the positions of floor slabs that act as props.

The consistency of the readings and checks carried out during construction confirmed the ELs' ability to monitor long-term movements reliably. The system since installation has been maintenance free, with the next sets of readings due in 2003. The advantage of fixed sensors over the conventional manual scanning inclinometer torpedo are frequency at which data is available and no labour cost in obtaining the data. The final cost of manual monitoring can be many times the cost of automatic monitoring systems in localised areas. Also on busy and congested building sites access to the top of the tubes to carry out manual monitoring can be difficult and once the excavation starts dangerous. A disadvantage of fixed sensor monitoring is that cables linking the sensors to the remote read station could be a problem. To overcome this slight disadvantage CMCS, have since 2000, been developing a radio transmit sensor that has been used successfully on several projects as outlined below.

Mansfield College, Oxford

The top down construction of a new chemistry laboratory at Mansfield College Oxford has typical access problems to the top of the diaphragm wall to take manual readings using a scanning inclinometer. The radio loggers with on site modem allow movements of the wall to be monitored at any time without need to visit the site. The system also includes radio crack monitors, thus avoiding unsightly cable runs on and in the buildings.

Biffa Land fill site Bromborough

The cost of monitoring movement of soft marine deposits beneath a new land fill cell at Bromborough are significantly reduced by radio communication between the site office and the strings of in-place electro-levels installed beneath the cell. The four strings of instruments are spaced at over 100m intervals. The furthest string is by the trees on the horizon in the photo opposite. The transmitters are battery powered and last for 12 months.

White City

Movements of the sheet piled diaphragm wall at White City were being monitored using CMCS radio loggers. The electro-levels are directly installed in the steel pipes welded to the sheet piles - three instruments only are used to monitor movements in the 9 m deep excavation. The system in each tube warn of wall movements making the system significantly cheaper than a manual system and also as accurate in terms of the magnitude of movements.