Study on seismic performance verification methods for performance-based design of gravity-type quay wall

Abstract

The essence of the performance-based design of gravity-type quay wall lies in the estimation of the performance of the wall after a seismic event. There are pseudo-static analysis and dynamic analysis as a performance verification method for the quay wall during the earthquake.

In pseudo-static analysis of gravity quay wall, the selection of an appropriate horizontal seismic coefficient is important for computing the equivalent pseudo-static inertial force. The definition of seismic coefficient is divided into the limit equilibrium based seismic coefficient (kh) and the performance based seismic coefficient (khk). The kh concept is based on providing capacity to resist a design seismic force, but it does not provide information on the performance of a structure when the limit of the force-balance is exceeded. There are conflicts among existing kh definitions regarding whether it considers 1) the effect of wall height on peak ground acceleration (PGA) used in determination of kh and 2) the application of correction factor for kh according to seismic performance grade. In order to overcome the limitation of the kh concept, the khk concept which can consider the performance of port structures exceeding the limit of force-balance was proposed in the technical standards and commentaries for port and harbour facilities in Japan, published in 2007. This study evaluates the relevance of these conflicts by reviewing the kh definitions in existing codes and guidelines for port structures and then by performing a series of dynamic centrifuge tests on caisson gravity quay wall. These tests were also used to validate that the khk concept evaluates the seismic performance of the quay wall accurately under various conditions. The reliability of the khk concept was evaluated for different wall heights, earthquake motions and the thickness of subsoil, which are the primary variables in the khk equation. In addition, some improvements that should be considered for the future revision of both the kh and the khk equations are discussed.

In dynamic analysis of gravity quay wall, generally using finite element or finite difference techniques with various constitutive models, provide a promising tool to evaluate precisely the performance of the structure considering the influence of the excess pore pressure on the behavior of soil and structure. In recent year considerable progress has been made in this area. However, numerical procedures need to be validated against physical data before they can be used in the field with confidence. Also, the development of a comprehensive numerical procedure so that engineers in the field can refer to them in order to perform the effective stress analysis reliably is required. The centrifuge test can be used to imitate the actual stress conditions and simulate the excess pore pressure and liquefaction by modeling saturated soil model. Accordingly, the dynamic centrifuge test has been used by researchers to study seismic response of port structures and validate the numerical procedure. In this study, two dynamic centrifuge tests were conducted using the gravity-type quay wall models at saturated soil condition to provide data for verifying the constitutive model of numerical simulation, and the test results were analyzed to assess the seismic behaviors of the quay wall and the saturated soil according to the liquefaction and the frequency characteristics of the input motion. In addition, the reliability of the dynamic centrifuge test was discussed by analyzing the dynamic centrifuge test results for the well-described record of actual cases of damaged quay wall during the earthquake in Korea.