Technical Services Group



Non-Destructive Evaluation of Railways and Rail Tunnels

Using Ground Penetrating Radar and High Resolution Imaging

By utilizing our IRIS Hyrail Vehicle, Penetradar is able to mount their antennas to inspect railways, the ballast beneath and any surrounding structure such as a tunnel wall.

Rail Tunnel Wall GPR Inspection

Penetradar's system developed for their roadway tunnel inspection can be utilized on railways by installing the system on a hyrail testing vehicle. More detailed information about how this tunnel inspection system works can be found on our tunnel and wall inspection page. This system employs ground penetrating radar (GPR) and high resolution imaging (HRI) technologies to detect and identify many types of tunnel liner/wall defects. It is entirely mobile, deployed quickly, and the process of collecting data is performed rapidly, thus, avoiding prolonged tunnel closures, and most importantly ensuring safety. This system, which is the first, if not only, commercial system of its kind, produces comprehensive and quantitative information on roadway or rail tunnel liner/wall condition.




Rail Ballast GPR Inspection

Rail tracks are conventionally positioned on ballast for reasons including economy, rapid drainage, and high load bearing capacity. As ballast ages, it is progressively fouled by fine-grained material that fills the void spaces between the aggregates, thereby inhibiting track drainage and reducing ballast life. The structural integrity of seriously fouled ballast will lead to track instability and, ultimately, train derailments. For this reason, it is crucial that fouled ballast be detected as early as possible.

Penetradar is able to use its high speed air-coupled horn antennas to investigate the structure of the ballast beneath the track. Up to six antennas (of multiple frequencies) may be used (3 on the front and 3 on the back) of the hyrail vehicle to conduct the subsurface investigation. Data collected by these GPR antenna can be used to determine the following:

  • Track Bed Structure (Ballast, Subballast & Subgrade)
  • Thickness of Layers
  • Ballast Fouling (Fouling Index)
  • Depth of Fouled Ballast
  • Moisture Content Measurement




High Resolution Imaging can also be provided to show the condition of the railway and surrounding areas.




After data collection and analysis, results can be provided as a series of superimposed, plan-view graphical images, each as its own separate layer. These layers can include mappings for:

  • Thickness of Layers
  • Ballast Fouling (Fouling Index)
  • Depth of Fouled Ballast
  • Moisture Content
  • Surface Imaging

Below are a sample of some of the map layers generated from the GPR data.



In addition to a graphical representation of mappings, the GPR information can be provided in an excel format, showing ballast fouling index and depth of fouled ballast, moisture content, ballast and subballast thickness (for each GPR antenna scan) versus mile post or station location on any desired increment needed.


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