Monitoring of Embankment Stability Using Embedded Coaxial Cables

The use of time domain reflectometry (TDR) to monitor movement in embankments and slopes is an emerging technology. TDR was originally developed for the telecommunication industry to locate breaks in cables. TDR is a time dependant pulsing electronic signal that detects changes in the impedance of a coaxial cable. Deformations, such as crimping or shearing of the cable, can be located quickly and accurately. By installing either vertical or horizontal cables in embankments or slopes, movement of slip planes, shear zones, or tension cracks can be easily detected. This paper reports on the use of TDR to monitor 20 to 30 feet high embankment levees in the Sacramento/San Joaquin Delta region of Northern California. Vertical cables were installed to monitor movement. In one installation, an adjacent inclinometer was installed and used for comparative data. The results show that a relationship exists between the inclinometer and TDR data. The location of the TDR cable signature spikes correlate with the zone of movement as shown by the inclinometer. In addition, the rate of spike growth correlates with the rate of levee slope movement. As a result, TOR appears to be an effective and economical method for embankment monitoring.