Fiber-optic high-resolution acoustic emission (AE) monitoring of slope failure

Abstract

We measured precursory acoustic emissions (AE) preceding the release of landslides in an inclined chute (3.0 m × 0.5 m × 0.5 m) filled with well-graded sandy soil. To detect elastic waves, we used an intelligent distributed acoustic sensing (DAS) technology. This method is based on fiber-optic technology that provides AE measurements at a high spatial and temporal resolution across large distances. The objective was to investigate acoustic emissions as precursors of slope failure and to assess the potential for landslide early warning based on this technology. We used a micro-sprinkler irrigation system to mimic triggering of landslides by rainfall. Fiber-optical cables were embedded within the soil material at three different depths. Additionally, we monitored occurrence of AE using independent piezoelectric transducers. Hydraulic monitoring of the wetted slope provided information on its hydrologic evolution and an audiovisual inspection system recorded deformations of the surface. Failure of the material was typically preceded by collapse of the slope toe followed by slowly accelerating retrogressive failure. This progressive failure resulted in an unambiguous acoustic signature captured by the DAS. Time-domain processing of waveforms provided insights into the prevailing failure mechanisms. The imminence of global failure was indicated by elevated AE activity. The fiber-optic AE detection using the iDAS™ (intelligent Distribute Acoustic Sensor) allows acquisition of failure-related elastic waves and may provide a valuable warning tool for large scale (km-scale) monitoring of shallow landslides and other rapid mass movements.