Structural Materials Technology NDT Conference 2000 Real Time Monitoring of Infrastructure using TDR Technology

Time domain reflectometry (TDR) is analogous to radar in a cable. A voltage pulse is propagated along a cable grouted into place. When the pulse reaches a deformity in the cable, a portion reflects. Location of the deformity is calculated by the time of flight of the reflection. Size and character of the deformity can be interpreted from the intensity and type of reflection. For example, a cable can be installed through a foundation into the underlying soil or rock. As movement occurs at the foundation/soil interface, the grouted cable is deformed, and reflected signals increase in intensity as the deformation increases. Signal propagation and acquisition are all digital and thus inherently allows remote data acquisition and storage as well as downloading via telemetry. Case histories of the use of TDR cables to remotely monitor possible deformation are summarized. These examples include, 1) cables in roadways above possible coal mine subsidence, 2) cables through scour critical bridge footings, 3) cables in a deforming rock causeway supporting a roadway, and 4) compliant cable and grout combinations in a deforming embankment. These case histories demonstrate installation techniques