Abstract
A lot of waterfront structures were damaged due to the 2011 off the pacific coast of Tohoku earthquake and subsequent tsunami. However, many river dikes and embankments display diverse damage patterns different depending on the topography and the types of structures. This paper analyzes the cause of damage to the Yoshihama river dike located in Ofunato city of Iwate prefecture based on several field investigations, in-situ testing, laboratory testing and numerical simulations. Damage analyses were performed for the dike that experienced compound disaster due to earthquake induced liquefaction and the tsunami that followed. Based on the in-situ testing and laboratory testing, it was found that there is likelihood of liquefaction in dike body having smaller modified N value. In addition, stability of the dike was numerically simulated under the action of the main shock, after shock and tsunami forces. Simulations revealed that loss of function and damage to the dike was greatly affected by the liquefaction and post liquefaction dissipation of the pore water pressure developed during the earthquake as well as the external force due to overtopping tsunami.
