Earthquake-Induced Flow-Type Slope Failure in Weathered Volcanic Deposits—A Case Study: The 16 April 2016 Takanodai Landslide, Japan

Abstract

The aim of this paper is to provide new insight into the catastrophic mobility of the earthquake-induced flow-type Takanodai landslide that occurred on 16 April 2016, which had fatal consequences. A geological and geotechnical interpretation of the site conditions and experimental investigations of the mechanical behavior of weathered Kusasenrigahama (Kpfa) pumice are used to characterize the landslide failure mechanism. The results of large-strain undrained torsional shear tests indicate that Kpfa pumice has the potential to rapidly develop very large shear strains upon mobilization of its cyclic resistance. To evaluate the actual field performance, a series of new liquefaction triggering analyses are carried out. The liquefaction triggering analyses indicate that Kpfa pumice did not liquefy during the Mw6.2 foreshock event, and the hillslope remained stable. Instead, it liquefied during the Mw7.0 mainshock event, when the exceedance of the cyclic resistance of the Kpfa pumice deposit and subsequent flow-failure type of response can be considered the main cause of the landslide. Moreover, the combination of large cyclic stress ratios (CSR = 0.21–0.35)—significantly exceeding the cyclic resistance ratio CRR = 0.09–0.13)—and static shear stress ratios (α = 0.15–0.25) were critical factors responsible for the observed flow-type landslide that traveled more than 0.6 km over a gentle sloping surface (6°–10°).

The Physical and Mechanical Properties of Single Pumice Sand Particle

“…2 The relationship between particle size and particle strength exhibits a negative trend, whereby an increase in particle size results in a decrease in particle stress. 3 The frequentist and Bayesian analyses of the linear relationship between particle size and particle stress do not exhibit significant differences due to the large sample size. 4 The relationship between the parameter aspect ratio and roundness coefficient with particle stress does not exhibit a significant correlation.…”

“…Pumice, a glassy volcanic rock with high pores, is white or pale grey to brown in color; pumice sand is subject to pulverization during seismic events, which may potentially induce landslides and liquefaction. Several regions with active volcanoes, including Indonesia, Japan, New Zealand, and the United States, exhibit pumice layers in multiple locations at some points attributed to the failure, which causes landslides or liquefaction phenomena [3][4][5][6][7]. To fully understand the behavior of pumice particles, it is crucial to consider both the general properties of pumice and the failures resulting from the presence of the pumice layer.…”