Measurement of landslide displacements using a wire extensometer

A continuous recording of landslide displacements is often required in order to better understand the complex relationship between the triggering factors and the dynamics of the movement. In this paper, we discuss the performance of the borehole wire extensometer and the interpretation of its results. The analysis for the case of a translational slide shows that the displacements measured with the wire extensometer are systematically smaller than the movements observed at the ground surface. A relationship between the wire readings and the horizontal component of the landslide movement has been established by means of three equations representing different stages of the wire displacement within the borehole. The applicability of these equations and the interpretation of the wire extensometer readings have been successfully checked at two landslide sites: Vallcebre in the eastern Pyrenees and Alverà in the Dolomites.