Bridge and Viaduct Monitoring, UK

The brief:

Mobilise immediately to site and set up an automated monitoring system to monitor the sections of track Murphy Geospatial installed the following sensors to the cross beams beneath the viaduct that carries the motorway and its heavy and busy loads.

16x automated total stations (mounted full length and networked over a distance of 1.6km).
3x automated in place GNSS stations (mounted at the start, middle, and end of 1.6km length of the viaduct).
1300x vibrating wire strain gauges and bespoke 12-channel wireless nodes to carry the sensors (mounted to the face of cross beams).
250x wireless bi-axial tilt sensor nodes (mounted to columns carrying cross beams).
1000x linear displacement sensors (potentiometers) and bespoke four-channel wireless nodes to carry the sensors.
12x 30m deep vibrating fully automated wire piezometers for water level measurement.
17x 30m deep vibrating fully automated wire extensometers for soil displacement between the various strata.
9x 30m deep in-place fully automated inclinometers for lateral soil displacement.

The challenges:

Murphy Geospatial was responsible for setting up the site compound and managing all site activities, such as logistics, health, safety, and welfare of the workforce, as well as occupational health during the installation period. The client visited the site multiple times during the 6 months installation period and was very satisfied with the order, cleanliness, and safety protocols.

Other challenges on the site were as follows:

Changing ground conditions
Winter weather
Working at height with machinery
Vandalism to equipment and trespassers on site
Working near mainline railway
Working over water
Repetitive strain injury and hand/arm vibration risks due to numerous drilling and fixing

Our work:

Over 2500 wireless sensors have been installed on this project. As part of the works, Murphy Geospatial had to follow strict quality plans and ensure that the works were conducted in line with the approved inspection and test plans. Testing all fixings for the structures has been conducted in line with British standards. Structural engineers have checked all temporary works designs to ensure that all instrumentation is safely installed to specification to ensure consistent data capture.

Over 2500 wireless sensors have been geometrically interlinked by surveying their exact position in the structure and adjusting the change of position of the structural elements according to local and global movement measured.

The whole sensors network has been designed and implemented from the large-scale monitoring of the global position at both ends and in the centre by GNSS(GPS) to a backbone of optical triangulation. This has been achieved by using 16 total stations permanently installed and evenly spaced under the viaduct to an array of reflectors that update the location of the columns and cross beams in 3D and related geotechnical boreholes along the alignment of the bridge to monitor underground movement and groundwater levels.

This is a fully automatic system with no manual monitoring required and uses all wirelessly connected multiple on-site PCs with a mobile phone data connection to the cloud-based visualisation software.

*GNSS Monitoring Station Installed Adjacent to Viaduct*

*Strain Gauge Network Installed to Cross Beams of Viaduct*

Ground monitoring sensors were installed beneath the viaduct. Each sensor installed in the thirty-eight boreholes drilled to an average depth of 30m has its own independent wireless transmitter that sends the data to the data logger installed beneath the viaduct. This information is then relayed to monitoring servers and displays the results in real-time on the web-based monitoring portal.

Piezometers shown in Figure 11 have been positioned at varying depths between 10m – 30m below ground level. This allows piezometric groundwater pressures to be determined. Using a vibrating wire 300kPa Piezometer with high air entry sintered filter tips.

Extensometers shown in Figure 10were manufactured during the drilling of the piezometer boreholes. They analyse the various strata levels and install the sensors at the several soil types. Boreholes have a varying number of sensors, from 3-6 in each borehole, depending on the number of different strata. The extensometers measure the displacement between the soil/stratum types.

Inclinometers shown in Figure 9 have been installed every 2m in each borehole to measure the inclination of the ground.

Our team:

Murphy Geospatial had a team of monitoring engineers, monitoring surveyors, a site manager, and a project manager on-site for 6 months to install all the systems, including communications. They had subcontracted some aspects of works such as ground investigation for temporary works designs and electrical contractors for powering the ATS and GNSS systems.

Results:

The monitoring data of the over 2500 wireless sensors, the optical instruments, the camera data, the GPS/GNSS, and the geotechnical borehole instruments are all streamed on the online portal for visualisation and security. The online portal shows a number of pre-configured report views, such as an overview of all the sensors as a map-view. This also shows the sensor status, from Green meaning all ok, to Yellow and Red for an alarming health condition. The entire system is fully geospatially referenced to the site coordinate system, and each sensor is shown on its real-world position.