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新潟県中越地震により発生した斜面災害

フォーマット:
論文(リポジトリ)
責任表示:
丸井, 英明 ; 吉松, 弘行 ; 渡部, 直喜
出版情報:
新潟大学積雪地域災害研究センター, 2004-12
掲載情報:
新潟大学積雪地域災害研究センター研究年報 = 新潟大学積雪地域災害研究センター研究年報
ISSN:
03877892  CiNii Articles  Webcat Plus  JAIRO
著者名:
巻:
26
開始ページ:
79
終了ページ:
86
バージョン:
publisher
概要:
This article deals with various types of landslide disasters induced by the Chuetsu Earthquake. The 2004 Niigata Chuetsu Earthquake triggered about 3800 landslides in various types and dimensions. It was general understanding until now that because of strong ground shaking during earthquakes, a lot of slope failures occur on the steep slopes with concave shape but only few reactivated landslides occur on relatively gentle slopes. However, also many reactivated landslides occurred in the neighborhood of the epicenters including strong aftershocks especially in the Yamakoshi Village this time. Landslide disasters induced by the earthquake can be classified mainly into the following categories: (1) Shallow slope failures on steep slopes near ridges, (2) Shallow slope failures on steep slopes along river channels, (3) Reactivated landslides on relatively gentle hillslopes, (4) Landslide dams were formed by the displaced soils mass by the previous three categories. For the mitigation of subsequent disaster, it was a matter of great urgency to implement emergency countermeasures against overtopping and failure of the landslide dams. Landslides occurred especially densely in the watershed of the Imo River along the Kajigane Syncline. Many landslides occurred along dip direction of geological formations. Originally, heavily landslide prone areas are widely distributed in the Tertiary mudstone areas in Niigata Prefecture. Reactivated landslides occur frequently in the eastern part of the Yamakoshi Village which consists of mudstone. This time most of landslides occurred in the western part of the Yamakoshi Village which consists of sandstone and sandy siltstone. More than 50 natural dams were formed along the main channel of the Imo River and its tributaries by the earthquake-induced landslides. There are two critical landslide dams because of their dimensions among them, namely Higashitakezawa landslide dam and Terano landslide dam. Both of them have the length of about 350m and the volume of more than 1 million m^3. The length of the buried river channel is about ten times of the maximum water depth of the reservoir in both cases. Therefore, the possibility of the destructive collapse of the dams by water pressure and piping were estimated to be low.<br />However, there remained apparent danger of overtopping and successive collapse of both dams. Therefore, the inhabitants of the downstream area had to evacuate. It was urgently necessary to lower the water table of the reservoir. The reservoir at Higashitakezawa formed by the largest landslide dam, which is located most downstream among five main dams, has a critical significance. In order to mitigate the danger of overtopping, the following emergency maneuvers were arranged. At first, the water table was tried to lower by pumps and siphons. At the beginning 6 pumps and after then additional 6 pumps were installed. Because of maintenance problems of the pumps, later an alternative diversion pipelines were installed as reserve measure for unexpected alarm cases. Finally, an open channel with a sufficient cross section area also for water discharge including snow melting during early spring was constructed. Lt was absolutely necessary to keep the stability of the displaced soil mass by the earthquake-induced landslide against the secondary landslide during construction works of the channel. Therefore, cutting operation of the upper part of the displaced soil mass was immediately carried out as an appropriate emergency countermeasure. Monitoring on displacement of soil mass was also arranged for the security during construction works. 続きを見る
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