© The Geological Society of London 2006 1 Development of a continuous 3D-monitoring system for unstable slopes using Time Domain Reflectometry

Abstract: In recent years Time Domain Reflectometry (TDR) has been introduced as a new system for landslide monitoring. Until now there have been no standards to define how to install cables or how to process the received data, especially when multiple TDR measuring points are connected to produce a 3D model of the deformation zone. A TDR system basically consists of two components: a coaxial cable and a TDR measuring device ("cable tester"). The cable is installed in a borehole and coupled to the surrounding rock with grout. If the cable is subject to deformation, this can be measured using the TDR cable tester. An electric pulse with an ultra-fast rise is applied to the cable and a reflection is detected. Changes in geometry caused by deformation produce characteristic TDR signatures. Since the propagation velocity of the signal is constant, the distance is determined by measuring the time between initiation of the pulse and detection of its reflection. TDR measurements are influenced by a great variety of parameters. Cable and grout type, water content in the surrounding ground and the number and type of deformation are a few examples. In the ongoing research attempts are made to define several different TDR measuring-system configurations (especially cable and grout type) where each is designated for a specific geological environment. These configurations are then calibrated in laboratory shear tests and finally tested in the field in real landslides, i