This study aimed to develop the evaluation method of coastal parapet levees’ seismic coefficients for level-1 earthquakes. In order to examine the applicability of frame analysis and acceleration response spectrum to the seismic coefficient evaluation, the numerical analysis and the model testing were conducted.
It was recognized that there is a difference between natural frequencies derived with the frame analysis and response analysis. The difference is increased with large acceleration seismic motions because of nonlinear stress-strain relation of ground. Decrease trend in natural frequency of parapet levees was represented since the natural frequency derived with the frame analysis was reduced with regard to stiffness reduction of ground with large seismic motions. It is realized that difference in equations of subgrade reaction coefficient in the frame analysis does scarcely affect calculation of natural frequency of parapet levees.
It is clarified that maximum acceleration of a parapet wall is estimated with response acceleration spectrum of high damping ratio at ground surface and barely influenced by natural frequency. The estimation of the maximum acceleration has more errors in case of large seismic ground motion as rotation of a parapet wall increases then. In cases excluding the seismic motions corresponding to level-2 earthquake, it is confirmed that maximum response acceleration of a parapet levee is estimated by natural frequency by the frame analysis and response spectrum with high accuracy. Examination with the numerical analysis and the model tests derived that the estimation method can be applied for seismic coefficient of coastal parapet levees for level-1 earthquake motions.

Key Words: Coastal parapet levees, model testing, numerical analysis, seismic coefficients, natural frequency