An integrated model simulating the initiation and motion of earthquake and rain induced rapid landslides and its application to the 2006 Leyte landslide |
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Authors: | Email author" target="_blank">Kyoji?SassaEmail author Osamu?Nagai Renato?Solidum Yoichi?Yamazaki Hidemasa?Ohta |
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Institution: | (1) International Consortium on Landslides, Kyoto, Japan;(2) Philippine Institute of Volcanology and Seismology (PHIVOLCS), Quezon City, Philippines;(3) GODAI Development Corporation, Kanazawa, Japan;(4) Ohta Geo-Research Co., Ltd., Nishinomiya, Japan |
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Abstract: | A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the
Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness
which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered
by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment
of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated
the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional
limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore
pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear
deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees
with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field
investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide
was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this
simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide. |
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