# Past, Present and Future Monitoring at the Vallcebre Landslide (Eastern Pyrenees, Spain)
###### Abstract  
Works carried out to monitor the displacements of the Vallcebre landslide (Pyrenees range, NE of Spain) since 1987 are presented. The landslide, which extends over an area of about 0.8 km\({}^{2}\) and affects more than 20 \(\times\) 10\({}^{6}\) m\({}^{3}\), has experienced displacements of up to one meter per year in some points and periods. It has been periodically monitored since 1987, using a wide range of surface and in-hole techniques: triangulation with theodolite, Terrestrial Photogrammetry, Electronic Distance Measurement, GNSS-GPS, inclinometers, wire extensometers, piezometers, DInSAR (satellite) and GBSAR (terrestrial). The results obtained using new techniques are compared with those obtained with GNSS-GPS and a wire extensometer, and checked against fixed stable points. From this comparison, we conclude that even though wire extensometers and inclinometers may have the highest precision, in practice, all systems play potentially valuable roles in providing meaningful data for monitoring at different study stages. In the near future, we envisage the installation of a Distributed Fiber Optic array to monitor the risk with a certain space and time continuity. After the evaluation of the precision and advantages of the different methods, the complementary use of some of them is strongly recommended. 2021  
Past, Present and Future Monitoring at the Vallcebre Landslide (Eastern Pyrenees, Spain)  
11 Department of Civil and Environmental Engineering, Division of Geotechnical Engineering & Geosciences, Technical University Catalonia (UPC-BarcelonaTech), 08034 Barcelona, Spain; [EMAIL_ADDRESS] (J.M. ); [EMAIL_ADDRESS] (J.C.) 1  
Footnote 23: email: email.difi.difi.difi.difi.difi.d.difi.d.difi.d.difi.d.difi.d.difi.d.difi.d.d.difi.d.d.d.difi.d.d.difi.d.d.d.d.difi.d.d.d.d.d.d.d.difi.d. The average slopes of both the topography and the basal shear surface in the middle and lower unit are gentle, i.e., in the range between 6 and 10\({}^{\circ}\). The basal shear surface depth is 42 m in the middle unit and 15 m in the lower one, being quite planar for most of the sliding surface. Complete information on the geology and geotechnics of Vallebebre, and a stability analysis, are beyond the scope of this article, but can be found in [1; 2; 3; 4; 5; 6; 7; 8]. Figure 3 shows a geomorphological sketch of the landslide and the location of the monitored points and boreholes. The most active area is the lower unit, whose toe is being eroded continuously by the Vallebe trorrent. Consequently, most of the monitored points were located there. The measurement of displacements is very often the simplest way to observe the evolution of a landslide and to analyze either the kinematics of the movement, the response to the triggering conditions (e.g., rainfall) or the efficiency of corrective measures. A variety of measuring techniques have been developed to track the movements of unstable areas (see i.e., [9; 10]). This second work, also known as the 'Red Book' of Geotechnical Instrumentation and Monitoring, is due to [PERSON]. Several of these methods have been used in Vallebebre since 1987, beginning with \"classical\" surveying and photogrammetry, and using Global Positioning Systems (GPS/GNSS) from 1995. In 1996, this site was included in the framework of the NEWTECH Project, funded by the European Commission. Between July 1996 and March 1997, 14 boreholes were drilled in the slope and equipped with inclinometers, wire extensometers and open standpipe piezometers (Figure 3). In 2004-2005, multipoint piezometers were installed in three additional boreholes. Later, the Vallebe landslide was included in an EU-FP7-funded research project known as SAFELAND. In 2007, seven artificial radar corner reflectors (CR) were installed to test  
Figure 3: Geomorphological scheme of the Vallcebre landslide superimposed over a vertical aerial image. Several GPS benchmarks, corner reflectors and borehole extensometers have been highlighted with symbols. the DInSAR monitoring capabilities.