Diminution de la vitesse des ondes de cisaillement précédant la fluidification d'un glissement de terrain argileux reproduit en laboratoire

International audienceClay slopes are susceptible to suddenly liquefy into rapidly accelerating landslides, thereby threatening people and facilities in mountainous areas. Because the shear-wave velocity (V s ) characterizes the medium stiffness, this parameter can potentially be used to investigate the rheological behavior of clay materials before and during the solid-to-fluid transition associated to such landslide failures. Previous rheometrical studies performed on clay samples coming from Trièves landslides (French Alps) have established that this material behaves as a yield stress fluid with a marked viscosity bifurcation. When the applied stress reaches a critical level, the viscosity decreases abruptly, along with V s which tends to zero in the fully fluidized material. Here, we monitor the Rayleigh wave velocity (V R ) variations in a saturated clay layer placed in a flume and progressively brought to failure by tilting the device. Experiments performed on clay samples with different water contents show a significant relative drop in V R values (and hence in V s ) before the onset of the mass movement. Additional rheometrical analyses point out that this precursory drop in V s is presumably due to a complex transient rheological response of the clay. These new results confirm that V s variations constitute a good indicator for monitoring clay slope stability

Application of ambient vibration techniques for monitoring the triggering of rapid landslides

International audienceAmbient vibration techniques are increasingly used for monitoring landslides. Two types of rapid landslides are considered in this study: mudslides in clayey sediments and rockfalls of intermediate size (10(3)-10(5) m(3)) in rigid rocks. The change of ambient vibration properties with time allows variations of internal mass characteristics to be obtained. This information is complementary to the surface motion measurements derived from air or ground based techniques and could be included in a monitoring system for landslides exhibiting a rapid mass movement