Abstract
Damage to earth structures for national highways by the 2004 Niigata-ken Chuetsu earthquake is reported. After overviewing damage to roads, several case histories on severe damage and rehabilitation work for national highways are documented. Immediately after the mainshock, national highways and prefectural roads were closed at 101 sites. Among them, main national highway routes Nos. 8, 17 and 116 were closed at 17 sites, while all of them could be re-opened within ten days after the mainshock. On the other hand, national highway route No. 291 that runs through mountaneous areas suffered from extensive damage at two sites, where alternative routes had to be constructed. The national highway route No. 291 suffered also from damage to embankments constructed on valley and/or landslide areas and damage to cantilever and gravity type retaining walls constructed in gorge area. The damage to the national highway route No. 17 included collapse of a gravity type retaining wall constructed on uncemented debris or weathered terrace deposits and collapse of a segmental retaining wall supporting a cut slope. The national highway route No. 8 suffered from embankment failures due possibly to liquefaction of a loose sand subsoil layer and/or concentration of longitudinal or transverse ground water flow.
