PSI - Issue 37

Koji Uenishi et al. / Procedia Structural Integrity 37 (2022) 404–409 Uenishi and Xi / Structural Integrity Procedia 00 (2022) 000 – 000

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1. Introduction Understanding the fracture dynamics of granular media is of crucial importance not only in physics, mechanical and civil engineering but also in earth and planetary science where examples range from landslides, debris flows and earthquake-induced structural failures to sample-return spacecraft missions. In our earlier study (Uenishi and Goji, 2018), therefore, as an example of earthquake-induced structural failures, a unique pattern found in a fill slope in Sendai, Japan, has been studied in light of dynamics of granular media. The failure is unique in the following sense: The 1978 Miyagi-ken-oki earthquake (moment magnitude M w 7.5) induced open (tensile) cracks in the top surface parallel to, but located some meters away from, the edge of the slope (see a cross-sectional view in Fig. 1(a)). Although reinforced after the 1978 quake using conventional countermeasures against body waves, the same slope failed exactly in the same manner due to the 2011 off the Pacific coast of Tohoku (Great East Japan) earthquake ( M w 9.0). It is noticeable that a theoretical study in 2010 before the 2011 event had already indicated the crucial role of Rayleigh surface waves due to dynamic impact (earthquake) in systematically generating the open cracks (Uenishi, 2010) (Fig. 1(b)). The transient development of stresses illustrated by the original version of the moving particle semi-implicit (MPS) method has also supported the idea of the more significant role of Rayleigh waves in a high frequency range than body waves that are conventionally assumed in engineering seismology (Fig. 1(c)) (Uenishi and

a

b

Incident Rayleigh wave

Open cracks

(Collapse of wet masonry retaining wall at some places)

Free surface

Reflected

Transmitted

Fill slope

House

Linear elastic medium

Natural ground (assumed)

c

R

H

Amplification in tension

Fig. 1. (a) Unique dynamic failure of a fill slope, tensile cracks at positions away from the edge, caused in Sendai City by the 1978 Miyagi-ken oki, Japan, earthquake. Both two-dimensional continuum mechanics-based analysis (b) and moving particle semi-implicit (MPS) simulations (c) suggest that a region of large dynamic tension may be generated at some distance from the edge due to the superposition of the incident and reflected seismic Rayleigh (R) surface waves in a linear elastic slope. In (c), the inclination angle of the slope is 75 degrees, and contours of the normalized maximum in-plane shear stress is shown for the case wavelength of the incident R wave is comparable to the slope height H . The normalized time t between the snapshots is c R t / H = 0.637 with c R being the Rayleigh wave speed (modified after Uenishi and Goji (2018)).