Numerical Assessment of the Contribution of Liquefaction and Directivity on the Seismic Displacement of a Quay Wall during the 2014 Cephalonia, Greece, Earthquakes

During the Cephalonia, Greece, 2014 earthquake sequence (M_w=6.1 and M_w=6.0), the quay walls in the port of Lixouri, Cephalonia, displaced laterally up to 1.5 m, while liquefaction of the gravelly port earthfills resulted in the manifestation of ground cracking and coarse-grained ejecta. To evaluate the seismic performance of the Lixouri port quay walls, numerical analyses using the finite difference method were performed at the location where the largest horizontal displacements were observed and the results are compared to the observed response. Three commonly used constitutive models (PM4SAND, UBCSAND, and URS/ROTH), informed by data from site investigation efforts (Dynamic Penetration Test, DPT, and Multichannel Analysis of Surface Waves, MASW), were considered for the simulation of the behavior of the liquefiable earthfills. The results of the numerical analyses indicate that liquefaction of the earthfills significantly contributed to the total lateral deformations of the quay walls; without liquefaction, the computed horizontal displacements are only approximately 30% of the observed lateral spreading when liquefaction occurs. Overall, the numerical analyses using best-estimate input parameters for the PM4SAND and UBCSAND models significantly under-predict the observed response, while the computed horizontal displacements are approximately 25% smaller than observed when the URS/ROTH model is used. The difference between model predictions can be partially attributed to the incorporation of residual shear strength once liquefaction is triggered when using the URS/ROTH model. Finally, the results of the numerical analyses show the strong influence of the pulse-like characteristics as well as the polarization of the input motion, indicating that forward directivity also significantly contributed to the observed response.