Dynamic Response and Deformation Analysis of a Marginal Wharf

Dynamic time-history analyses were performed for a pile-supported marginal wharf using the two-dimensional (2D) finite difference numerical modeling program FLAC (Fast Lagrangian Analysis of Continua, Itasca Consulting Group, Inc.). The wharf includes a soil embankment constructed to retain the dredged fill material placed behind the embankment. Due to high potential of liquefaction in the native sandy/silty soils and hydraulic dredged fill behind the embankment during the design earthquakes, ground improvements were incorporated into the design. These included deep soil mixing (DSM) and Vibro-Improvement (e.g., vibro-compaction and/or vibro-replacement). Ground improvement using wick drains and surcharge was also considered for the native soft fat clay that underlies the wharf area to accelerate the consolidation process and to increase the strength during construction. The main objective of the dynamic analysis was to evaluate the extent of ground improvements required to stabilize and limit the deformations of the embankment during the design earthquakes. Excessive embankment deformations adversely impact wharf foundation and performance, and therefore, need to be limited to an acceptable value. In the FLAC analyses, the Mohr-Coulomb soil model was combined with the hysteretic damping FLAC SIG3 function to model the non-linear behavior of the soils during earthquake shaking. This FLAC damping function was calibrated with the results of the 1D site-response analysis obtained using the program D-MOD2000 (Geomotions, LLC), so the dynamic soil parameters used in these two models are consistent for the free-field ground condition. This paper presents the approaches, assumptions, and results of the above analyses.