Damage to Geotechnical Structures in Waterfront Areas of Northern Tohoku Due to the March 11, 2011 Tsunami Disaster

The 2011 off the pacific coast of Tohoku Earthquake and the associated tsunami brought disaster to many soil structures. This paper summarizes the investigation results of waterfront structures in the northern area of Tohoku region (Aomori prefecture and northern Iwate prefecture). The investigations focused on the geotechnical and structural aspects of the damages to coastal dikes, quay walls and breakwaters due to the earthquake and the tsunami as well as the backrush. Analyses of the damage and their nature indicate that, in the north of Tohoku, rather than the earthquake itself the compound disaster brought by the tsunami was more rampant. The investigations reveal that the force of tsunami, the force of overtopping tsunami and the force of backrush were responsible for the scouring of the mound of breakwaters and seawalls resulting in the catastrophic failure of such structures.