DYWIDAG Case Study
Wigan Culvert Examination using Elios 2
PROJECT NAME: Wigan Culvert Examination
AREA: Greater Manchester
NETWORK RAIL ROUTE(S): LNW
SERVICES: Drone visual examination; image analysis; defect reporting
The utilisation of drones to conduct examinations of structures in a broad range of settings, including the rail environment, is a well-established practice and has been commonplace for around 5 years. However, this has been constrained to exterior, “open-air” operations as drones are dependent on receiving GPS signals to ensure stability when in flight. Interior examinations in GPS-denied environments have been problematic as “conventional” drones must be flown in manual mode and due to their size, are difficult to control and have only limited capability.
To that end, GeoAccess invested in leading-edge technology in 2019 and acquired the Flyability Elios 2 confined-space inspection drone. With the ability to fly in GPS-denied environments, the drone is enclosed in a collision-resistant cage and can be used safely in tight spaces where obstacles are present.
A dual camera capability in both video and infra-red allows a broad range of examinations to be conducted. Still images captured from the video footage can be used to construct photogrammetry models and low-density point-clouds, enabling engineers to view assets in 3D and take relative measurements of the structure and defects.
Flight-crews are experienced in working in the rail environment and have the relevant qualifications such as STE02 and STE04 certification, PTS, Dynamic Risk Assessment and First Aid. Our examiners have at least 5 years of experience conducting examinations of a broad range of structures including airshafts, bridges, culverts, retaining walls and tunnels. GeoAccess pilots have carried out numerous examinations of a range of structures with the Elios 2.
GeoAccess recently conducted an examination of a large structure that conveys the River Douglas underneath multiple lines 200m east of Wigan North Western Station. Gaining access to the structure previously, using traditional methods, has been complex, difficult, and expensive. The river is enclosed by high retaining walls and direct access is not possible.
Access by boat and examiners using pole-cams is dependent on river height and flow strength, and launch points are several hundred metres away, involving lowering the boat and the examiners by rope systems – costly and not without risk. Erecting scaffolding on the riverbed is a prolonged, logistically complicated, and expensive process. Tensioned rope access systems are possible, but set-up is complex, involving closing the lines above and would require multiple personnel with an associated increase in risk.
To eliminate disruption to the running of trains, not require a day or night possession and discount using traditional methods of access, the client approached us with a view to using a drone to carry out the examination in daylight hours.
Their key requirement was the ability to view areas of the structure that cannot be seen from river level and areas where the use of other access systems would be constrained, prohibitively expensive and incur risk to personnel.
Our solution was to use the Elios 2 and after briefing the client on its capabilities they agreed it was the right tool for the task.
To overcome the access issue a two-person flight-crew (also rope access qualified) were suspended in cradles at the downstream end of the structure and the Elios 2 was hand-launched and recovered for successive flights.
Using the Elios 2 we were able to carry out a visual examination in several hours, with a particular emphasis on difficult access areas such as the underside and recessed elements of the structure. This represents a significant reduction in time, resources and costs when compared to traditional methods, which would have taken several days at the very least. A total of nine flights were completed, with each flight focussing on a particular area and elements of the structure, and 70 minutes of 4K video footage was obtained.
The Elios 2 was easily able to access areas on the underside of the structure that could not have been viewed from river level, nor easily reached by means such as scaffolding. Recessed areas would have required task-lighting for illumination in order for the examiners to carry out their work – not an issue for the Elios which has 10k lumen lighting system.
Upon completion of the site works the video footage was uploaded to Flyability Inspector, a software application that is used to view and analyse the video. Points of interest, including defects and areas of concern, were then created by selecting individual frames from the video by a structural examiner.
These frames were then annotated, with approximate measurements of features taken from the image where appropriate.
A number of defects were identified, including cracked padstones, corrosion of various degrees to the metallic elements and large accumulations of pigeon droppings, the latter being a health hazard if the structure had been examined by personnel rather than by drone. Using the Inspector software results in much less time being spent on analysis and reporting.
The normal approach would have involved the examiner analysing potentially hundreds of images captured by camera. As a result, delivery of the final report can be achieved in several days, rather than in weeks.
Successful delivery of the project, by using a drone for the examination of the structure and specialist software for analysis and reporting, in a much-reduced timescale resulted in significant time and cost savings for the client and importantly, reduction in risk to the personnel carrying out the work.