A novel technique to monitor subsurface movements of landslides

Slope deformation sensors (SDSs) were developed to monitor profiles of soil deformation at a high frequency during slope-monitoring and landslide-triggering experiments. It was hypothesized that the surface and subsurface movements could be combined to integrate the temporal development of the movements and help monitor the initiation and propagation of the shear bands indirectly, as well as predict the volume of the eventual landslide. Four SDSs were installed in a 38 degrees slope in Northern Switzerland and slope movements due to two artificial rainfall sprinkling experiments in October 2008 and March 2009 were monitored. This paper describes the design, numerical validation, installation details, and performance of the SDSs during the first rainfall event. The data acquired from SDSs in terms of bending strain, deformation profiles, and an indication of the mechanical energy transmitted from the surrounding soil are analysed and compared with the patterns of surface movements of the slope and changes in the horizontal earth pressure. The findings are interpreted based on the applied rainfall, hydrological properties of the slope, bedrock shape, and specifications of the observed failure surface in the subsequent landslide triggering experiment. Details of the data acquired from SDSs during the second experiment in March 2009 are reported and analysed in a forthcoming paper.