Browsing by Author "Abey, Lulseged"

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    Static and Dynamic Lateral Response of Single Piles Using Kerr-Equivalent Pasternak Subgrade Model
    (Addis Ababa University, 2021-09) Abey, Lulseged; Asrat, Worku (PhD)
    The most widely used model to perform piles analysis under static and dynamic lateral loads consists of modeling the pile as beam elements and representing the soil as a group of unconnected, concentrated springs perpendicular to the pile (Discrete Winkler Model). The absence of interaction between the individual springs in the Discrete Winkler Model produces an unrealistic response. This study aims to perform an analytical and numerical study of the static and dynamic response of the pile-soil system under lateral loads (considering homogeneous soil profile) using a two-parameter subgrade model. In order to develop a rational method that includes shear interaction between the concentrated springs, a two-parameter model proposed by Worku (2014) was used. A simplified expression for the adopted model parameters was obtained by performing a series of numerical and parametric investigation. The proposed model was calibrated using outputs from PLAXIS 3D, and from the result, it was observed that the proposed model could predict pile-head stiffness within a maximum error of 3% when compared to FE output. A new approach for determining the critical pile length is also introduced. Using this new approach, critical pile lengths for different boundary conditions are introduced. Based on the variation of pile-head stiffness, a new classification, other than "short" and "long" piles, was introduced, namely "transitional" piles. Simplified expressions for pile head stiffness for piles in a "transitional" state are provided. The dynamic stiffness (or impedance) and the kinematic response are investigated. Equivalent spring and dashpot coefficients at the pile-head are computed to provide a simplified procedure to replace the entire soil-pile system with a spring and a dashpot at the top that will produce the same effect on the overlying structure. Equivalent spring coefficients at the top of the pile are obtained from the beam on elastic foundation techniques. Equivalent damping coefficients are obtained following a simplified approach that uses the concept of conservation of energy. Results are compared with those given by a dynamic finite element (DFE) analysis over a range of frequencies for piles in a homogeneous soil layer, and from the result, it is evident that the model is in good agreement with the DFE results.