Seismic response of hunchbacked block type gravity quay walls

Highlights

• The performance of port structures should be checked on the basis of earthquake hazard.

• A series of 1-g shaking tank tests was performed using a 1/10 scaled block type quay wall with gravel backfill materials on firm non-liquefiable sea bed conditions subjected to different harmonic loads.

• The back-face shape of the hunchbacked walls is found to be an important factor and the larger positive slope of the wall improves the overall seismic stability.

Abstract

Earthquakes near major cities may cause big social and economic impacts. Damages to port facilities may cripple the economy. The past twenty years’ experience has proven the high vulnerability of the port facilities. This fact, along with the economic importance of port structures, indicates the need for better seismic design approaches for berth structures and cargo handling facilities. In the recent decades, there have been many incidences of failure of gravity type quay walls. These failures have stimulated research interest in the development of performance-based design methods. In this paper, two different hunchbacked block type quay walls with different back face shape were studied. A series of 1-g shaking tank tests was performed using a 1/10 scaled block type quay wall with gravel backfill materials on firm non-liquefiable sea bed conditions subjected to different harmonic loads. The shaking tank tests provided insight into the wall displacements and the total dynamic pressures by analyzing pressure components at the contact surface between the saturated gravel backfill soil and the wall. It is concluded that the back-face shape of the walls is an important factor and the larger positive slope of the wall improves the overall seismic stability.

Introduction

Ports are the main components of maritime transport and they have an important role on commercial transport, hence any damage level is undesirable. Most of the port structures have been located in highly seismic regions and the supporting quay walls are also subjected to earthquake loadings in addition to water wave action and vessels berthing loads. Therefore, the performance of existing port structures should be checked on the basis of earthquake hazard.

Seismic risks at ports have not received sufficient attention and only a limited number of studies has been carried out for the assessment of block type quay walls, which are widely preferred in most of the ports. Yuksel et al. [17] documented and discussed the distribution and the extent of damage and serviceability of marine structures after 1999 Kocaeli Earthquake (M_w = 7.52). The effects of earthquakes, including severity of damage, service losses, and environmental impact at petrochemical facilities, were severe and extensive. Sumer et al. [14] presented a state-of-the-art review of seismic-induced liquefaction with special reference to marine structures.

The seismic response of a port structure is affected by the interaction of the structure with the surrounding and underlying soil, and water. This effect, widely referred to soil-structure-water interaction (SSWI), is a rather complex phenomenon and involves a number of difficult-to-assess problems. One basic problem is the change in amplitude and frequency content of seismic waves when they interact with an inclusion in a propagation medium. This kinematic interaction is initiated when incident seismic propagation away from the causative fault and through the geologic media encounter a structural element or foundation element whose inertial and stiffness characteristics differ from those of the surrounding soils. As these incident ground waves hit the structure-foundation, they are both reflected and refracted. The resulting transmitted waves are the source of inertial interaction and generate inertia forces by exciting the overlying structure, which further alter the motions of the foundation and the surrounding soil (ASCE, 1998).

Researchers have focused on seismic performance of waterfront structures for longer than a decade and a number of research studies have been carried out both experimentally and numerically. It is very important to learn the lessons from past case studies to better understand the vulnerability of waterfront structures exposed to earthquake.

Experimental and/or analytical studies by Miura et al. [9], Fujiwara et al. [3], Mohajeri et al. [10], Mendez et al. [8] and Nakahara et al. [11] were presented to assess the dynamic response of gravity type quay walls. Additionally, Inoue et al. [5], Kim et al. [7], Kim et al. [6], Towhata et al. [16] and Yuksel et al. [18] approached the problem through experimental and/or numerical approaches. There exist also purely numerical studies performed by Alyami et al. [1], Arablouei et al. [2] and Tiznado and Rodriguez-Roa [15]. Most of these studies were focused on understanding the response of caisson type quay walls. Hence, in the literature there exists a gap in understanding the seismic performance of block type quay walls. Sadrekarimi et al. [13] investigated the static and dynamic behavior of hunchbacked gravity walls by considering back-face shape of wall. Sadrekarimi [12] also studied the seismic performance of gravity type broken back quay walls through 1 g shaking table model experiments and proposed a simplified sliding block analysis model for estimating lateral displacements, which is calibrated with the experimental results. However, the blocks had shear keys at the top and bottom surfaces to prevent relative sliding.

A contemporary design philosophy for port structures in seismically active regions is expected to suggest assessment methodologies for the estimation of seismically induced foundation, backfill and wall deformations along with the stresses acting on them. Unfortunately, conventional (force-balance) methods are not well suited to fulfill these expectations. While performance-based design procedures attempt to assess the deformation and stress demand and capacity of the systems however appropriate earthquake performance levels needed to be defined along with acceptable block type quay wall damages. Despite their wide use as a quay wall, in the literature there exists a gap on acceptable performance criteria.

This study attempts to assess the static and dynamic performance of the block type quay walls in the form of lateral displacement and tilting as well as settlement of the backfill and is hoped to contribute to close this gap.

In this study, reduced scale models of two different hunchbacked quay walls with different back face shapes were prepared in 1-g shaking tank. The scale ratio of model to prototype was selected as 1/10. Tests were performed on firm bottom conditions and a dense backfill material was used for the purpose of fully concentrating on the response of quay wall and eliminating the effects of soil liquefaction on the overall response.