Transport infrastructure
Rail
Rail managers face many pressures including the need to build a better record of the condition and construction of railway assets and a drive to improve safety by separating the people working on the railway from the trains operating on it. Geophysical and Non Destructive methods play a key role in both initiatives.
Non destructive and geophysical surveys provide condition and construction information quickly and without significant disturbance or damage to the assets under investigation. Surveys are quick and use highly portable equipment, making for safer work practices than ‘traditional’ methods such as excavation and drilling. The results can provide a ‘big picture’ based on continuous rather than point measurements to enable more cost effective decision-making and better management of railway assets.
Fugro
Aperio personnel are qualified and experienced in railway working and can undertake
integrated investigations of track, structures and stations.
Fugro Aperio is an approved supplier
of geophysical surveys to the UK rail industry and is registered under the
Achilles Link-up scheme.
Members of the Aperio team have been working in this field since the mid-eighties and have unrivalled experience of rail infrastructure investigation. The company has a proud record of innovation as recognised by the 2003 SMART award for development of systems for high speed trackbed surveys.
We recognise the value of calibrating and verifying geophysical results by targeted intrusive work. Track surveys are most effective when calibrated by trial holes, embankment surveys with boreholes, and structural surveys with careful exposure of selected features.
Trackbed condition and thickness surveys
Ground Penetrating Radar (GPR) surveys have been adopted as a best practice element for all Network Rail track renewal projects and provide a continuous view of the ballast thickness and condition. GPR is a powerful tool in preventing 'wet beds' and hard spots which have an adverse affect on ride quality and lead to rapid deterioration of the track. GPR is used to:
- determine depth of ballast
- map ballast/formation intermixing
- map contamination and moisture (although distinguishing the two is not always possible)
- detect shallow services and structures that could damage track maintenance machinery .
Clients have found the ability to detect ballast pockets (areas of thick ballast due to differential settlement) particularly useful, as these are invisible at the surface and can indicate underlying formation problems such as low bearing capacity, unstable slopes, voids or unrecorded structures at depth. Surveys can also detect damage from infestation by burrowing mammals, such as rabbits or badgers, which can lead to void migration up to the track.
3D
plot for track ballast profile from GPR
Investigation of the track subsurface by GPR is complicated by reflections from reinforced concrete sleepers and by contaminants in the ballast. By using very rapid scanning GPR systems Fugro Aperio can provide high quality data, even in challenging conditions. Our rail team has developed innovative software processes to reduce the effects of sleepers and other unwanted signals to provide a clearer image of the ballast and formation materials.
Surveys can be conducted at two levels:
Network / Route surveys
Typically conducted from a survey vehicle or train, at a rate of tens or hundreds of kilometres per day, providing an overview of ballast and sub-ballast thickness and condition. Coverage can include the area between and outside the rails. High speed acquisition means coarse data sampling. Generally reported in lean formats for efficient input to client asset management systems and comparison with track geometry and other machine data.
Detailed site investigation
Typically conducted at walking speed from a hand pushed trolley or a road rail vehicle. Surveys can include unique supporting technologies such as ultrasonic ballast surface profiling which reduce the effects of ballast surface variations and help identify changes at the bottom of the ballast that are more significant to track performance. Coverage of full track area including embankments if required, often used in conjunction with other geophysical methods and targeted intrusive methods. Multi channel radars and high data density maximise resolution of challenging targets such as buried services. Generally reported in data rich formats tailored to meet client needs.
Penetrometer survey to verify GPR investigation of trackbed
and formation.
Detailed
track surveys are conducted using a 4 channel radar system which provides rapid
progress and detailed information from 2 profiles in the four foot and one
outside each sleeper-end.
Concrete Sleeper Testing
Track surveys also include concrete sleeper testing and Fugro Aperio has considerable knowledge of methods to determine concrete sleeper configuration and condition. A multi-test sleeper testing approach combining specialist ultrasonics and GPR was developed by Aperio and Railtrack in 2001. Since then the approach has been refined and used to identify sleepers requiring replacement ahead of a numerous track renewal projects including sites on the UK West Coast Route.
Investigation of cavities and structures below the railway
Geophysical methods can be used to locate cavities such as solution features or mineworkings, and structures such as hidden culverts and infilled arches within embankments.
A contract in one Network Rail territory involved Fugro Aperio teams surveying embankment sites throughout the territory using Ground Resistivity and GPR with a high level of success in defining the location, shape and depth of culverts and disused occupation arches. The surveys also proved effective in identifying any sign of disturbance or movement within the trackbed and formation materials above the hidden structures. Mapping old mineworkings and solution features often involve the use of microgravity, a method that maps changes in ground density by tracking minute changes in gravitational fields.
Applications of geophysics include:
- mapping 'lost' structures such as unrecorded culverts, drains, infilled bridges etc. through embankments
- mineworkings, shafts and adits
- voids from burrowing animals such as rabbits and badgers
- karstic solution features, swallow holes, caves etc.
- earthworks investigation, for example to provide information on ground profile and properties.
Non destructive investigation of railway structures, platforms and buildings
For information investigation of railway structures platforms read our structural investigation pages.
Ground resistivity profile over a 'lost'bridge structure within
a rail embankment