Using Time-Domain Reflectometry to Monitor Subsurface Void Propagation

Time-Domain Reflectometry (TDR) was originally used in geoengineering to locate caving heights above longwall coal mines. TDR is a geotechnical instrumentation technique utilizing a coaxial sensor cable grouted in place (usually vertically) in bedrock or soil, designed to deform or break as the surrounding material collapses or moves. The TDR cable is read using a reflectometer, and the resulting waveform can be used to determine the depth and severity of subsurface movement. Its use can also be extended to provide constant, automated data collection in locations where known potential sinkhole hazards exist. In two case studies, TDR was installed to monitor subsurface movement along roadways where subterranean voids resulting from human activities threatened infrastructure at the surface. In the first case, a highway in Colorado suffered a sinkhole collapse into an abandoned railroad tunnel below. After repair of the sinkhole, TDR was installed to monitor other segments of the roadway that overlie the tunnel and could have similar collapse features. The second case involved an abandoned mining cavern below a developed area in the central United States. Each of these scenarios required a means to monitor the upward propagation of voids, and provide warning to the appropriate personnel in the event of subsurface collapse. The TDR sensor cables were connected to an Automated Data Acquisition System (ADAS), which read the TDR cables, stored data, analyzed the data, and sent email alerts in the event of sensor movement. Each ADAS was accessible through the internet by an IP-addressable cellular telephone modem.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References;
  • Pagination: pp 307-321
  • Monograph Title: Proceedings of the 65th Highway Geology Symposium (HGS 2014)

Subject/Index Terms

Filing Info

  • Accession Number: 01640000
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jun 27 2017 1:03PM