Hydrographic Survey & Monitoring at Collapsed Rail Bridge

Hydrographic Survey & Monitoring at Collapsed Rail Bridge

About This Project

A 20-metre section of the viaduct across Malahide Estuary on the main Belfast – Dublin train line collapsed when ground holding the track gave way, slipping into the estuary below. An emergency response survey team was called upon to begin a range of high level monitoring of the immediate area and vicinity. The major traffic on the bridge (90 trains a day) required immediate action.
To initially assess the scene of the incident and provide real-time monitoring data of all the structures involved (above and below the waterline) and located in the immediate vicinity. The surveys aimed to ascertain the cause of the accident, prevent a re-occurrence and assist designers and engineers in the design and build of the replacement structure.
Murphy Surveys were called on site less than 24 hours after the incident occurred. Firstly, a full Laser Topographic survey of the area and all structures surrounding it was carried out and the data captured generated a 3D map of the site from a remote location. This map was used for “forensic” and safety purposes in approaching the site.
Once the site was fully assessed, monitoring equipment was installed to avoid further movement and further damage on the bridge.
Firstly, monitoring prisms were installed along the deck and high precise levelling was required to monitor the settlement of the structure, while electronic tilt monitoring equipment was installed on the four surrounding piers. During re-construction, three vibration sensors were installed across the length of the bridge to monitor vibrating activity. A range of hydrographic surveys and hydrographic monitoring was also required as the prime suspected cause of the incident was recent seabed erosion.
Daily bathymetric surveys on the east and west sides of the viaduct were carried out to enable us to monitor the stability of the slope and the scour hole that was identified. Cross sections were then produced from this data and cross referenced daily. We also carried out a bathymetric survey that extended 2km east and west of the railway viaduct to create a hydrodynamic model of the area for reinstating the weir to the correct level. In addition to that, electronic water level gauges were placed on both sides of the viaduct to establish the relationship between the incoming and outgoing tide. The information gathered was then passed to the hydrodynamic modellers to calibrate the model and establish the impact that construction or development would have on the area.
To overcome the unique elements and conditions of the site, we specifically commissioned bespoke seawater proof tilt sensors.
All the monitoring data captured on site (underwater, piers, temperature, bridge, vibration) was channelled directly and in real-time via wireless connection from each sensor placed around the site directly to our central monitoring observation point (which could be located anywhere: only requirements were a PC and Internet connection). Tolerance parameters were agreed with Irish Rail and all monitoring systems were set up to raise an alarm should anything be recorded outside of these parameters.
Daily reports of all measurements and recorded activities were produced where movements recognised on the monitoring targets were immediately evident. As a result of the specialist monitoring software used by Murphy Surveys, we had the ability to observe the readings in real time and produce quality monitoring reports very efficiently in PDF or in excel tables for further extrapolation and interpolation. See more about our Hydrographic Survey services.

Key Points

  • Given the location of the bridge, Murphy Surveys in collaboration with Geodata developed bespoke sea-water resistant tilt sensors and cables to be installed underwater.
  • Working hand in hand with the Irish National Rail Network engineers, Murphy Surveys prevented further damage from occurring: when the vibrations caused by heavy duty machinery and equipment for the re-construction on site exceeded the safety requirements, the works were stopped and the re-construction re-organised to meet the safety requirements, despite the pressure from many parts.
  • The long-term monitoring of the bridge allowed us to spot seasonal influences on the structure, which have been taken into consideration to prevent accidents in the future.


Iarnrod Eireann is the Irish National Rail Network Operator responsible for all urban, suburban and rural train and tram routes nationwide.

Survey Type

3D Laser Scanning




August 2010 - October 2013


75,000 m sq


Laser Scanner
Total Station


Case Studies, Laser Scanning & BIM, Monitoring Solutions, Specialist Engineering, Surveying & UAV
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