阪神・淡路大震災-防災研究への取り組み-河川堤防はいかにあるべきか-地震による被害が示すもの-

Abstract

The great earthquake attacked Hanshin area of Kobe, Asiya, Nishinomiya, Amagasaki and Osaka and Awaji island have destroyed many buildings and civil works, and also damaged the embankments and revetments of many rivers. Field survey in Hanshin area and interviews with river engineers of the ministry of construction, Hyogo and Osaka prefectural offices. The sate of damage is presented here.In Hanshin area, 90 rivers have been damaged by the earthquake and 353 damaged places have been listed up by the officials (Feb.1, 1995). Collapse of embankment and ground fissures on the dike were reported, and overturning and cracks of revetment were observed at so many places. About 70 percents of seriously damaged places were in Hyogo, where many buildings and houses collapsed. Overturning of revetment and ground fissures are caused by the strong seismic force, however, some embankments near the river mouse collapsed because of the liquefaction of the ground.In Takaha River, the stone revetment destroyed over 100 m long. Same damage was observed in another rivers in Kobe. This area was attacked by the severe flood in July of 1938 and 695 persons were dead and missing. As rivers in this area were very steep and sabo works not enough, debris flows occurred and destroyed the bank of rivers during the flood. After the flood stone revetment as shown in the photograph was constructed, however, the reinforcement with concrete was not enough. The left-side embankment of Yodo River in the downstream area (0 to 3 km from the mouse) collapsed. It is considered that the cause was the liquefaction of the ground. The height of the dike decreased up to 3 m. This dike was designed as flood and storm surge countermeasures and covered with concrete at front, top and back of the bank. The bank was destroyed completely. Fortunately there was no tsunami.The bank of Kanzaki River in the downstream area sank 10 to 15 cm, and the 680 m crack was observed on the asphalt paving of the top, and the maximum subsidence of the paving was 60 cm, however, the function of the bank as the flood and storm surge countermeasures has not been lost. As sheet and tube piles are used for the earthquake resistant design, severe damage has been prevented. Embankment has been designed to prevent the flood disaster, however, this earthquake has taught us that such a design is important to keep the function of the embankment and to prevent the secondary disaster after the earthquake.