ABSTRACT
ABSTRACT: A detailed reconnaissance survey was made at the Daikai subway station, which was the first subway structure that had completely collapsed due to earthquakes. The station is a box frame structure with a column at the center, measuring 17 m wide and 7.17 m high in the exterior dimensions and 120 m long. A complete collapse occurred at more than half of the center columns, which resulted in the failure and collapse of the ceiling slab and subsidence of subsoil over the station by more than 2.5 m at maximum. Many diagonal cracks were also observed on the walls in the transverse direction. Judging from the damage patterns, a strong horizontal force was imposed on the structure from the surrounding subsoil. Evidence of damage due to vertical force was not clearly observed. Finally, characteristics to be used in the future analysis in order to make the mechanism of collapse clear are shown through the numerical analyses.
