[S13-6] Earthquake source mechanics VI

[S13-6-01] Photoelastic Study of Dynamic Stress Transfers in Granular Media

^○Koji Uenishi¹, Tsukasa Goji¹, Wojciech Debski² (1.The University of Tokyo, Tokyo, Japan, 2.Polish Academy of Sciences, Warsaw, Poland)

In our earlier study (JpGU Meet. 2008, AGU Fall Meet. 2009), using a high-speed camera, we conducted fully-controlled laboratory experiments associated with large dynamic deformation of granular materials that may be observed, e.g. in earthquake faulting and landslides. Especially, as a fundamental investigation, our attention was paid to transient granular mass flow from a (semi-)cylindrical column consisting of dry granular materials (glass beads). We traced the particle movement and development of slip lines inside the granular column that was set on a rigid horizontal plane and collapsing due to the action of gravity, and showed, for instance, the influence of frictional properties of the horizontal plane and beads on the average flow velocity and the final shape of the collapsed column. However, the details of stress transfers in granular media subjected to such dynamic deformation have not been well clarified yet. Therefore, here, as a preliminary observation for deeper understanding of stress transfers and propagation of waves and rupture inside granular media, experimental technique of dynamic photoelasticity is used. Penny-shaped photoelastic particles (diameter 20 or 40 mm) made of epoxy resin are prepared and placed on a rigid horizontal plane, and dynamic impact is given to a particle by a gun-launched projectile (impact velocity 50-80 m/s) or by another free-falling photoelastic particle (impact velocity 2-3 m/s). The transient stress transfers are recorded by a high-speed camera at a frame rate of up to 100,000 fps. In a single particle system, where only one particle is situated on the plane, dynamic wave propagation is recognized inside that single particle, but in a layered multi-particle system stress is transferred quasi-statically from a particle to neighboring ones and wave propagation is not clearly identified. This may suggest preloading (and more static contact between each particle) is needed for visualization of waves in the layered system.