Suggested Method to Predict Catastrophic Landslides

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1994(1) Investigators and joint researchers from Canada, U.K., New Zealand, Sri Lanka, and China held a joint research meeting for two weeks in Kyoto, and made a joint field investigation in Mt.Mayu Landslide area, Nagasaki Prefecture, Japan.1995(2) Sassa and Fukuoka investigated Frank Slide, Canada with Evans of Geological Survey of Canada. Terrace soils were sampled from where the slide ran away and brought to Japan. They carried out undrained loading ring shear tests for predicition of landslide movement with the sample and found that the apparent friction angle was only 3.8 degrees, which could explain its longrunout. Evans found sheared layr beneath the deposited mass of the Frank Slide by boring.(3) Sassa, Fukuoka and Evans jointly investigated the Nikawa landslide, Nishinomiya, Japan which was triggered by the 17 January 1995 Hyogoken-Nambu earthquake. They sampled soils there and carried out undrained cyclic loading ring shear tests. Results showed "sliding surface liquefaction" occurred due to destruction of soil structure and grain crushing. This phenomenon reduced the shear strength rapidly and dramatically and could explain the rapid landslide motion.(4) Investigators and joint researchers from Canada, U.K., New Zealand, United States, and Italy gathered at Kyoto University and held a joint research meeting for two weeks, and discussed on the practical method of landslide prediction and assessment.1996(5) Sassa Fukuoka carried out field investigation of the 6 December 1996 Gamaharazawa Debris Flow Disaster. They sampled torrent deposits from the nearest stream. Undrained ring shear tests on the sample revealed that the sliding surface liquefaction occurred and initiated high speed shearing, which could explain the landslide triggered debris flow mechanism. Sassa discussed the results with Investigators and joint researchers form United States and Canada at the occasion of IUGS (International Union of Geological Sciences) meeting.