Analysis of seismic damage mitigation for a pile-supported wharf structure

This paper evaluates earthquake-induced permanent ground deformations and the structural response of a typical pile-supported wharf structure built over loose granular fill. Using numerical simulations for a suite of 55 reference seismic ground motions, we investigate the effectiveness of an array of PV drains installed behind the pile-supported deck in mitigating structural damage associated with deformations of the fill. Numerical analyses use a sub-structuring approach in which the 'free-field' 2D coupled deformations, and seepage within the soil fill are simulated using the u-p formulation in the OpenSees finite element framework. The complex non-linear and inelastic stress-strain properties of the sand under cyclic loading are represented using the Dafalias-Manzari (DM2004) bounding surface plasticity model, while customized 1-D finite elements are used to describe flow in the PV drains. The resulting ground deformations and excess pore water pressures are treated as boundary conditions in modeling the response of the wharf structure, through macro-elements that represent local pile-soil interactions (after Varun and Assimaki, 2012 [1]). We discuss the associated soil behavior and show how lateral spreading is mitigated by the proposed PV drain array. This mitigation system limits the potential damage to the pile-deck connections enabling much simpler structural retrofit for the wharf.