Remote Monitoring Of Unstable Slopes Using Time Domain Reflectometry

Time domain reflectometry (TDR) was originally developed to find breaks in power and communication cables. When a coaxial cable is deformed, the impedance characteristics of the cable change. Changes in impedance are noted as changes in the characteristic TDR signature of the cable. This technology has been adapted to monitor slope and embankment movements. Coaxial cables were placed in boreholes and slope movements monitored remotely by a cable tester and computer at the site, or by using a data logger and cellular phone. Four sites in California were monitored using TDR and the data compared with conventional inclinometer monitoring. Results showed that TDR can reliably determine the depth and location of shear planes. The advantages of TDR are that: 1. cumbersome equipment need not be brought to, or maintained at, the site to monitor movement; 2. slope monitoring can be done from any location with a modem and computer, and 3. installation and monitoring can be economically accomplished. The result is increased safety, and a considerable cost savings.