Estimating Slope Movement with Time Domain Reflectometry (TDR)

Time domain reflectometry (TDR) has been used in the past to locate and estimate movements in landslides encroaching highways. As part of this study, further research of TDR and landslide monitoring was performed to evaluate if readings obtained from TDR can be correlated with the amount of movement along a slide plane. Field measurements obtained using side by side or nearby slope inclinometers and TDR cables were compared. In addition, laboratory tests were carried-out using a cable shear-testing device designed to simulate the slide plane conditions found within a landslide. The following issues were examined in relation to both the field and lab studies: (1) the amount of slide plane movement required to detect a TDR reflection reading in the cable; (2) the amount of movement associated with a TDR reflection as the slide mass continues to move; and (3) the influence of installation conditions on TDR readings. Based on the results of this study, tentative relationships between slide plane movement and TDR reflection readings are discussed. However, these relationships depend upon cable type, grout strength, and soil at the shear interface.