Performance of Countermeasures Against Massive Slope Failures in Sendai City During the 2011 Tohoku Earthquake

抄録

This paper presents a case history of extensive damage due to large-scale slope failure during two successive earthquakes and the positive impact of countermeasures in Midorigaoka, Sendai, Japan. We detail damage during the two earthquakes, postquake countermeasures, and problems encountered during restoration. The area was damaged during the 1978 Miyagiken-oki Earthquake, after which countermeasures were deployed. The most significant damage was at Midorigaoka 1-chome, where 18 houses were demolished and two areas were abandoned. Extensive countermeasures such as a collecting well, landslide prevention piles, and retaining walls were implemented here. In Midorigaoka 3-chome, 14 houses were demolished and two areas were abandoned. Landslide prevention piles were installed and a landslide-controlling dam constructed. Failure was only superficial at Midorigaoka 4-chome, so no heavy remedial work was needed. The Midorigaoka district was hit again by the 2011 Tohoku Earthquake, although no damage was observed at 1-chome. Damage at 3-chome resembled that in the 1978 earthquake. Ground movement of up to 1–2 m was induced at Midorigaoka 4-chome, where approximately 100 houses collapsed and the area itself was forbidden for housing use. The degree of damage during this earthquake depended upon countermeasures adopted after the 1978 earthquake.