Analysis of the Aso-Bridge landslide during the 2016 Kumamoto earthquakes in Japan

In 2016, earthquakes occurred beneath Kumamoto City, Kumamoto Prefecture in the Kyushu Region of Japan and generated numerous landslides around the city, and among those triggered in this disastrous event, the Aso-Bridge landslide was the largest. For the purpose of examining the behavior of this large-scale landslide during the main shock of the Kumamoto earthquakes, we conducted a study involving simplified sliding block concepts and finite element codes, and conclude that (a) the slope of the Aso-Bridge landslide (about 710 m high and with a dip angle of 33 °) is marginally stable in the absence of earthquakes; (b) the failure surface obtained using finite element codes is in satisfactory agreement with that of the actual failure surface; ©) our results reveal that the initiation-time of the Aso-Bridge landslide lay between 18.45 and 21 s based on three indications: (I) the directional tendency of the first apparent displacement, (ii) evidential factor of safety (FS) values <1, and (iii) Newmark’s displacement; and (d) the combination of an internal friction angle of 35 ° and a cohesion value of 80 kPa led to a failure surface closest to that observed in the field. The study demonstrates that we were able to apply the simplified sliding concepts and finite element codes to analyze the Aso-Bridge landslide in reasonable agreement with the actual event.