| Many geological disasters and accidents on civil engineering structures have occurred over the last 10 years in Japan. We collected and analyzed the lessons on the view point of geo-risk management. The most various disasters were induced by strong earthquakes such as the 2011 Off the Pacific Coast Earthquake. Damaged structures were tunnel, bridge, dam, embankment, cut slope etc. Major disaster types were landslide and slope/ground deformation. The most important lesson is necessity to estimate probable disaster types in planning stage of structures. In the last 10 years, some disaster types became to be considered in structure design. For example, ground deformations by active faults and slope deformations in earthquakes are newly considered in the Specifications for Highway Bridges by Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT) after the 2016 Kumamoto Earthquake. On the other hand, major accident types were deformation and collapse of structures induced by ground excavation. Damaged structures were mainly tunnel and cut slope. These accident types have been already considered in the technical standards, nevertheless similar accidents tend to be repeated. The most epoch making accident was the giant sinkhole accident in Fukuoka city in 2016 induced by the collapse of a tunnel under construction. The tunnel has been excavated just several meters under the surface of unconformity between Paleogene sedimentary rocks and Quaternary deposits. The causes of the accident are irregularity of unconformity surface, strong inhomogeneity of the weathered and jointed rock mass, and misunderstanding of these natural geo-risks. It is impossible to prevent the accident only by technical standards because the accident was mainly induced by man-made risk. After that, MLIT has decided to start geo-risk management. In this presentation, some trouble cases and important lessons for geo-risk management are demonstrated. |
