Quay Wall Stability Considering Earthquake and Tsunami Overtopping Forces Together in the Active Condition

Abstract

In 2011, off the Pacific coast of Tohoku, Japan, an earthquake triggered a tsunami that struck the coast; the region was inundated with the tsunami and earthquake aftershocks continued for days. Coastal structures were mostly overtopped by the tsunami and subjected to seismic aftershocks in this compromised state. This paper investigates the stability of a quay wall subject to the combined effects of tsunami wave overtopping and seismic action of an earthquake using the limit equilibrium method. The tsunami’s force was calculated using a numerical program. More specifically, the force of the tsunami’s waves acting on the front, top, and back sides of the quay wall was estimated. The backfill material behind the wall was assumed to be permeable coarse sand. The stability of the quay wall was assessed for both sliding and overturning in the active condition. When an earthquake and tsunami were considered together the stability of the quay wall decreased significantly. In addition, the stability of the wall varied significantly before the wave hit, upon the initial arrival of the wave, and after overtopping by the wave. Once the tsunami hit the wall, the factors of safety for both sliding and overturning increased significantly since in this active condition the tsunami acted as a resisting force rather than a driving force. However, after the tsunami overtopped the wall the factor of safety decreased until it reached its minimum value. The overtopping tsunami increased the driving force on the back of the structure, which decreased the factor of safety.