| Implementation of performance-based design procedures for pile-supported waterfront structures involves estimation of the dynamic wharf response for hazard scenarios that include liquefaction of the backfill. In these cases, empirical techniques based on quasi-static observations and widely implemented in practice for the analysis of dynamic soil-pile interaction problems, may not be used to address the role of critical parameters such as soil permeability, rate of loading and residual soil strength in the wharf performance, nor simulate radiation damping phenomena for liquefiable soils in transient loading. On the other hand, very few experimental results exist on dynamic soil-pile interaction effects in liquefiable sites to justify the development of generic mechanical elements for this class of problems.As part of this research, a macroelement is developed for soil-structure interaction analyses of piles in liquefiable soils, which captures efficiently the fundamental mechanisms of saturated granular soil behavior. The mechanical model comprises a nonlinear Winkler-type model that accounts for soil resistance acting along the circumference of the pile, and a coupled viscous damper that simulates changes in radiation damping with increasing material non-linearity. Three-dimensional (3D) finite element (FE) simulations are conducted for a pile in radially homogeneous soil to identify the critical parameters governing the response. The identified parameters, i.e., hydraulic conductivity, loading rate of dynamic loading, dilation angle and liquefaction potential are then expressed in dimensionless form. Next, the macroelement parameters are calibrated as a function of the soil properties and the effective stress. A semi-empirical approach that accounts for the effects of soil-structure interaction on pore pressure generation in the vicinity of pile is used to detect the onset of liquefaction. The predictions are compared with field data obtained using blast induced liquefaction and centrifuge tests and found to be in good agreement.Finally, the macroelement formulation is extended to account for coupling in both lateral directions. FEM simulations indicate that response assuming no coupling between the two horizontal directions for biaxial loading tends to overestimate the soil resistance and fails to capture features like 'apparent negative stiffness', 'strain hardening' and 'rounded corners'. |
