Prediction Of Seismic Response And Damage Mitigation For Pile-Supported Wharf Structures

Abstract

Many ports in the US are located in areas of high seismicity and remain vulnerable to damage from large earthquake events. Waterfront structures such as pile-supported wharves are particularly vulnerable to damage associated with lateral spreading of the underlying loose soil fills. This paper describes results of analyses to understand the performance of a typical pile-supported wharf and the effectiveness of mitigation measures. The analyses use a sub-structuring approach in which the ‘free-field’ response of the soil fill is simulated using finite element analyses that are able to represent the complex non-linear stress-strain properties of sands under seismic loading using the model proposed by Dafalias and Manzari (DM, 2004). Ground deformations and excess pore water pressures are then treated as boundary conditions in modeling the response of the pile-supported wharf structure, using a macro-element proposed by Varun and Assimaki (2012) to represent local soil-structure interaction. The paper presents the performance of the pile-supported wharf for a suite of 56 ground motions, and highlights the occurrence of deep-seated failure mechanisms in the supporting rows of piles. The effects of lateral spreading in the soil fill can be addressed by installing full-depth Pre-fabricated Vertical (PV) drains at locations behind the crest of the fill. Analyses with this mitigation system show that structural damage is limited to the pile-deck connections enabling much simpler designs for structural retrofitting.