Dynamic Lateral Response of Single Piles Considering Soil Inertia Contributions

Abstract eng:
In the most widely used model for analyses of piles under lateral loads, the discrete Winkler model, the pile is modeled as beam elements and the soil is represented by disconnected, concentrated springs normal to the pile axis. The literature shows that for dynamic analyses of piles, the soil stiffness and damping properties can be adequately included through lumped springs and dashpots, whereas no lumped masses are added to represent the soil inertia effects. The objective of this paper is to present a simple model to represent the soil that includes its inertial effects and to investigate their importance on the dynamic response of single piles. The proposed methodology is based on a lumped model consistent with the Winkler proposition. The parameters of the discrete model were obtained by approximating the continuous (plane strain) model developed by Novak. In the proposed approach, the pile-soil interaction is accounted for by three frequency independent elements: a spring with stiffness ka, a mass ma, and a dashpot with coefficient ca. The spring-mass-dashpot coefficients representing the soil are defined by simple equations. The proposed model was used to demonstrate that a lumped soil mass is not required for small/medium soil Poisson’s ratios. However, consideration of the soil mass was found to be important for soil deposits with high Poisson’s ratios (e.g., undrained loading of saturated soils where ν = 0.5). For the case of saturated soils the inertia contribution due to the soil lumped masses is of the same order of the pile mass.

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