Experimental study of acoustic emissions from granular flows
IPGP - Îlot Cuvier
Séminaires de Sismologie
The seismic signal generated by rockfalls, landslides or avalanches is a unique tool to detect, characterize and monitor gravitational flow activity, with strong implication in terms of natural hazard. Farin et al.  have shown, theoretically and experimentally, that the properties of an impacting bead (mass and velocity) on smooth surfaces can be retrieved from the emitted seismic signal (radiated elastic energy and mean frequency). In this work, an extension to rough and erodible surfaces is proposed. Steel and glass beads of diameter 2 to 10 mm are dropped from 10 to 30 cm heights on: (i) a PMMA plate alone to test smooth surface as a reference experiment, (ii) stuck glass beads on the PMMA plate to create roughness, and (iii) free glass beads lying above the stuck ones to investigate erodible bed. Beads of 2 mm or 3 mm separately are used for the surfaces (ii) and (iii). The characteristics of the acoustic signal (frequency, energy) generated during the impact is measured thanks to 8 accelerometers (sensitivity [1, 56] kHz) and the bead motion characteristics (kinetic energy lost, bounce angle) is monitored using both these accelerometers and stereoscopy view captured by 2 fast cameras (500 im/s). The Hertz model validity to describe impacts on a smooth surface is confirmed. For rough and erodible surfaces, the scaling laws evolutions between source properties and signal characteristics are established phenomenologically and discussed.