Practical Applications of Time Domain Reflectometry (TDR) to Monitor and Analyze Soil and Rock Slopes

Time domain reflectometry (TDR) has been used for many years in the telecommunication industry to locate damage or faulting in communication cables. More recently TDR has been applied in the geotechnical/geologic field in order to detect movement and locate shear planes in rock or soil slopes by grouting coaxial cables in boreholes. TDR can provide significant cost savings over traditional inclinometers in many applications as well as be remotely accessed. This paper presents five case histories in which TDR has been successfully used to monitor and analyze unstable rock slopes and soil embankments. Case histories cover a range of applications which include an open pit rock slope, a small rock slope, two embankment/levees over soft/loose soil, and a native soil slope. In addition to monitoring for soil movement, the last case history also presents the innovative employment of TDR to measure changing groundwater levels in an economical remote sensing configuration. This paper also summarizes testing equipment, cable selection, and cable installation methods for each case history.