Monitoring of Deep-Seated Mass Movements

A GPS monitoring system has been developed for the investigation of landslides. The applicability of this system is demonstrated by monitoring the deep-seated mass movement Gradenbach, Austria. 17 GPS surveys of at least 48 hours duration each were carried out during the last seven years. The motions can be determined with an accuracy of 4 mm in horizontal direction and 8 mm in vertical direction. The accurate GPS results suggest that the velocity pattern of the deep-seated mass movement at Gradenbach is not uniform but rather intermittent, i.e., highly accelerated motions are followed by periods of creeping. The causes for this pattern are unknown.
For the investigation of the mechanics of this phenomenon a strain rosette for in-situ measurements of local distance changes is being developed. It consists of three embedded extensometers at a separation in orientation of 120°. The sensors are long gauge (5 m) fibre optical interferometers of SOFO type yielding a precision of 2 μm for absolute length changes and 0.01 μm for relative length changes. The concept, design and first test results will be presented.