11:15 AM - 11:30 AM
[HDS05-08] Earthquake-induced and rainfall-induced tephra layered shallow landslides and geotechnical properties of tephra materials
Keywords:Tephra, tephra layered shallow landslides , geotechnical properties, Sliding layer, Physical properties, Mechanical properties
In recent years, tephra layered shallow landslides due to earthquakes and heavy rainfalls have repeatedly occurred in specific tephra layers (volcanic ash layers) in volcanic regions in Japan. In recent years, the Izu Oshima landslide disaster caused by heavy rainfall in 2013, the Kumamoto earthquake in 2016, and the Hokkaido Eastern Iburi earthquake in 2018 have occurred in Japan. Especially in the Aso region of Kumamoto Prefecture, not only earthquakes-induced landslide disasters but also heavy rainfall-induced landslide disasters in 1990, 2001, and 2012 have repeatedly occurred.
Tephra layered shallow landslides caused by an earthquake or heavy rain could be characterized by the occurrence of a sliding surface in a specific volcanic ash layer. Focusing on the sliding surface of the tephra layer, we have continuously studied the geotechnical characteristics of these tephra layers. In this study, the sliding surface was observed at the site where tephra layered shallow landslides occurred, and undisturbed and disturbed samples were collected from the tephra layer where the sliding surface occurred. Mechanical properties, physical properties, saturated permeability properties, and content of clay minerals on sliding and surrounding tephra layers were investigated.
Results from the study of Hokkaido Eastern Iburi earthquake in 2018 reveal that the physical properties of sliding layers from two landslides demonstrated the same characteristics: non-plastic soil with a low density of soil particles, void ratio, and dry density; these characteristics could influence earthquake-induced landslides.
This study is also focused on the monotonic and cyclic direct shear behaviour for the tephra layers to understand the mechanism of landslide during earthquake. Constant vertical stress and constant volume cyclic direct shear tests were performed to study the cyclic behaviour of the tephra layers. From the constant vertical stress test, strain hardening behaviour was observed. From the constant volume test, shear displacement increased largely during cyclic loading, despite the tephra layer being in an unsaturated state, which were similar to the behaviour of saturated sand during liquefaction.
Characteristics of physical properties and mechanical properties of the sliding layers in shallow landslides of tephra materials on earthquake-induced and heavy rainfall-induced landslides were discussed.
Tephra layered shallow landslides caused by an earthquake or heavy rain could be characterized by the occurrence of a sliding surface in a specific volcanic ash layer. Focusing on the sliding surface of the tephra layer, we have continuously studied the geotechnical characteristics of these tephra layers. In this study, the sliding surface was observed at the site where tephra layered shallow landslides occurred, and undisturbed and disturbed samples were collected from the tephra layer where the sliding surface occurred. Mechanical properties, physical properties, saturated permeability properties, and content of clay minerals on sliding and surrounding tephra layers were investigated.
Results from the study of Hokkaido Eastern Iburi earthquake in 2018 reveal that the physical properties of sliding layers from two landslides demonstrated the same characteristics: non-plastic soil with a low density of soil particles, void ratio, and dry density; these characteristics could influence earthquake-induced landslides.
This study is also focused on the monotonic and cyclic direct shear behaviour for the tephra layers to understand the mechanism of landslide during earthquake. Constant vertical stress and constant volume cyclic direct shear tests were performed to study the cyclic behaviour of the tephra layers. From the constant vertical stress test, strain hardening behaviour was observed. From the constant volume test, shear displacement increased largely during cyclic loading, despite the tephra layer being in an unsaturated state, which were similar to the behaviour of saturated sand during liquefaction.
Characteristics of physical properties and mechanical properties of the sliding layers in shallow landslides of tephra materials on earthquake-induced and heavy rainfall-induced landslides were discussed.