PSI - Issue 13

Koji Uenishi et al. / Procedia Structural Integrity 13 (2018) 769–774 Uenishi and Goji / Structural Integrity Procedia 00 (2018) 000–000

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unsatisfactory consequences for the design of earthquake-resistant slopes. This point of view may be supported by the fact that although reinforced using conventional body wave-based countermeasures after the 1978 event, the same slope failed in Sendai in 2011.

Open cracks

Incident Rayleigh wave

(Collapse of wet masonry retaining wall at some places)

Free surface

Reflected

Transmitted

Fill slope

Linear elastic medium

House

Natural ground (assumed)

b

a

Energy source

R

H

c

Amplification in tension

Fig. 1. (a) Typical failure of a fill slope in Sendai, Japan, caused by the 1978 Miyagi-ken-oki earthquake. (b) Two-dimensional linear elastic slope model used in the continuum mechanics-based analysis. Large dynamic tension may be induced at some distance from the slope edge owing to the superposition of the incident and reflected Rayleigh waves in the top surface. (c) An example of simulations of dynamic Rayleigh surface wave (R) interaction with a model slope (inclination angle 75 degrees) utilizing a numerical particle method. The development of normalized maximum in-plane shear stress is shown for the case c R T R / H = 1 with c R and T R being the Rayleigh wave speed and the duration of energy source pressure, respectively. Dynamic amplification of tensile stress due to the superposition of the incident and reflected Rayleigh waves is visible in the top surface. The time t elapsed from the excitation of the energy source is normalized as c R t / H = 2.762, 2.975, 3.187, 3.399, 3.612 and 3.824 (from top left to top right and then from bottom left to bottom right) (modified after Uenishi and Sakurai (2015)). 3. Dynamic failure of granular slopes The above analytical speculations have not been experimentally confirmed yet. Here, therefore, dynamics of dry granular media is experimentally investigated. Special attention is paid to propagation of waves and fracture, if any, inside the media. Photoelastic penny-shaped particles (diameter 8 mm, thickness 3 mm) are cut out from birefringent polycarbonate plates by a laser cutter, and 407 out of them are piled up on a rigid horizontal plane to form a two- dimensional model slope with some inclination angle, e.g. 60 degrees in Fig. 2. Impact load is given to the top free surface of the slope by free-falling button-shaped aluminum (Fig. 2(a)) or by a projectile launched using an airsoft gun (Fig. 2(b)). The temporal stress changes and fracture development are traced by a high-speed digital video camera