Estimation of permanent displacement of gravity quay wall under seismic loading by numerical analysis

Abstract

Recently, earthquakes such as Gyeongju and Pohang earthquake have occurred in Korea for the last two years. After these events, it becomes very important to precisely predict seismic responses and behavior of structures and to apply results in the design of structures under earthquakes. Gravity quay walls are usually utilized as retaining structures of port and harbor facilities. Discussions on the development of old and new harbor structures are underway in Korea. Seismic performance evaluation has become important as Korea is no longer safe from earthquakes. Researches on the behavior of gravity quay walls under seismic loading have been significantly conducted in Japan. Since Hyogoken-Nambu earthquake in 1995, many quay walls were damaged in Kobe port. Therefore, many researchers have been studying the behavior and stability of the walls during earthquakes. On the other hand, in Korea, there are not many precedent studies in this field. Also, there is a limitation to applying Japanese research methods to the design of gravity quay walls in Korea. Because the geological characteristics of Korea are different from those of Japan, bedrock exists within 30 m mostly. Therefore, gravity quay walls at Ulsan port were used to take account of geological characteristics in this study. In this study, permanent displacement of gravity quay walls as one of retaining structures has been evaluated under seismic loading condition with numerical analysis in ABAQUS and analytical analysis with Richards-Elms and Whitman-Liao methods. Numerical analysis is performed using nonlinear soil model with von Mises criteria to describe strain hardening behavior at small strain deformations. Verifications of von Mises model are implemented by (a) comparison of backbone curve from ABAQUS and shear-stress curve as input data and (b) comparison of the soil ground acceleration between ABAQUS and DEEPSOIL, 1-D seismic site response analysis. The permanent displacement can be categorized into (a) displacement by slip failure and (b) overturning displacement after the slip mode by active earth pressure from the backfill. First, the displacements by slip failure model were estimated when ground acceleration at the surface of the backfill behind the wall exceeds yield acceleration by Mononobe-Okabe method using several earthquake motions. And then, the results were compared with analytical analyses using Richards-Elms and Whitman-Liao methods. Second, case study was conducted to investigate the effect of PGA on the permanent displacement. The permanent displacement using PGA and PGV of the ground acceleration at the surface of the backfill was estimated by numerical analysis and Richards-Elms method using five motions scaled to 0.3 g and 0.5 g. In this study, the permanent displacements were estimated by the numerical analysis and the analytical analysis. And the, although Richards-Elms has a difference in results depending on the seismic motions, the methods can partially estimate the permanent displacement of gravity quay walls as port structures. Whitman-Liao methods estimated the permanent displacement of gravity quay walls more conservatively than Richards-Elms method and it is not appropriate for the walls as port structures.