STUDY ON THE VIABILITY OF TERRAIN CONDUCTIVITY AS A RAILWAY SAFETY SURVEYING TOOL

Train derailments are a common occurrence in the Appalachians, particularly in West Virginia. In the spring of 2001, a project was set forth by the Nick J. Rahall Appalachian Transportation Institute and Marshall University to develop a mobile railway safety monitoring system. It is hoped that a vehicle carrying various non-invasive geophysical instruments can be created to monitor the subsurface condition of the track area, and forewarn any impending geological hazards. One geophysical instrument purchased for the project is the Geonics EM 31.

The EM 31 is a conductivity measuring survey tool that is capable of locating subsurface anomalies to depths of up to 20 feet. Multiple instrument orientations allow the lateral extent and geometry of these anomalies to be determined. Examples of the detectable anomalies are joints, voids, faults, and many other geologic phenomena. The main advantage of the EM 31 is the speed at which surveys can be performed. In the continuous survey mode the EM 31 can take a sample every .4 seconds. With an effective lateral range of approximately 4 meters, complete survey coverage could theoretically be achieved at speeds of up to 80 miles per hour. This is much faster than the monitoring vehicle would conduct surveys, but it proves that vehicle speed would not be an issue.

A major concern of any electromagnetic surveying is cultural interference from man-made objects. A possible source of interference is the rail track itself. If the rail track caused the conductivity values to be erroneous, then the EM 31 would not be implemented on the vehicle in the future. Multiple surveys were conducted in Lexington, KY and the Huntington, WV area in an attempt to assess the effects of the rail track on EM 31 measurements. A particular rail survey in Huntington examined two adjacent sections of railway. One rail track was complete and still in operation, the other had been decommissioned, with the rails removed, but the ties and ballast still remained. It was found that, with the exception of one anomaly, the results from both sections were similar. This indicates that the rail tracks have little to no effect on the results, provided that the EM 31 surveys are conducted parallel to the track. This, coupled with its high speed survey capability, makes the EM 31 a viable candidate for inclusion on a rail stability monitoring system.