2:00 PM - 2:15 PM
[HDS10-02] Slope failures induced by the 2020 July heavy rain in the Chubu Region
Keywords:plutonic rocks, welded tuff, accretionary complex, artificial slopes
A weather front stayed in July, 2020 brought much rainfall to the Japanese Islands. As well as the Kyusyu Region, the Chubu Region including Gifu, Nagano and Aichi Prefectures were also suffered from slope disasters in various localities. An overview of the landslides occurred in the Chubu Region from geological and geomorphological standpoints is mentioned. The following cases were observed as slope failures. 1) Shallow rapid landslides on the slopes consist of pulutonic rocks and welded tuff: At Nishibora, Takayama city, Gifu Prefecture, both Mesozoic medium-grained granodiorite and crystalline welded tuff ("Nohi Rhyolites") are strongly weathered into decomposed sandy saprolite (Masa). Many slopes collapsed at the surface no more than 1 m depth, maximum width is 20 m. 2) Deep-seated rapid landslides on the slope of Jurassic accretionary complex: Weathered sandstone of the Mino Belt were in failure at Okudabora, Gujo City, Gifu Prefecture, and Kamiya, Kiso Town, Nagano Prefecture. Weathered meta-chert with small amount of granite and diorite of the Ryoke Belt were collapsed at Toko, Tenryu Village, Nagano Prefecture. Depths of landslides reach about 20m in the Okudabora and Toko, and their volumes are 50,000 m3 and 100,000 m3, respectively. In the case of Kamiya landslide, only two surface failures are visible, but they are located at the toes of larger deep-seated landslide of which 400 m wide. Also, the Okudabora landslide occurred in the larger gravitational deformed area. 3) Artificial slope failures in suburban area: Cut slope for railroad were collapsed by flooding water flowed from a road above the slope at Oshikamo, Toyota City, Aichi Prefecture. Embankment for widening of dwelling site along a terrace scarp broke involving retaining wall at Okacho, Okazaki City, Aichi Prefecture.