Time Domain Reflectometry for Monitoring Highway Slope Movements: FHWA-WY-06/03F
A study of time domain reflectometry was conducted for application to monitoring of highway slopes. Laboratory shear tests were carried out in an attempt to develop a correlation between shear displacement and TDR signals from grouted cables in sand deposits.
Laboratory tests were also conducted to evaluate the potential use of air-dielectric, or hollow, coaxial cable for measuring groundwater elevations and for combined measurements of groundwater and slope movements. Grouted cables were installed at roadway landslide sites at four locations in Wyoming and monitored for periods ranging from one to six and a half years.
Results of laboratory shear tests demonstrate that cable deformation is sensitive to boundary conditions and that it is difficult, if not impossible, to obtain consistent, repeatable results. Each test yielded a significantly different relationship between cable signal and shear deformation. It is concluded that no reliable correlation can be established for laboratory test conditions. Hollow-cable TDR was found to provide a quick and reliable method for determining groundwater elevations and is recommended for field implementation.
Four landslide sites were instrumented with coaxial cable for TDR monitoring and slope inclinometer readings. Results are presented and discussed in detail. TDR readings are compared to slope inclinometer readings at each site. Based on the lab and field testing results, it is concluded that TDR can be a cost-effective and useful method for monitoring the occurrence and depth of slide planes when applied appropriately. TDR is not sufficient to establish the magnitude of slope deformation. Recommendations are given for continuing implementation by WYDOT of TDR for slope monitoring.