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Finite element implementation of a model to estimate the permanent strain of cyclically-loaded soil

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2020
Babaoğlu, Muhittin
In vast majority of geotechnical structures such as monopile or strip foundation, which are subjected to repeated loading, long-term resilience of the structures is directly related with the behavior of granular materials subjected to cyclic loading. Repeatedly loaded structure distributes stress to soil that surrounds the structure. When granular materials are exposed to cyclic loading, plastic strain occurs despite the applied stress is less than plastic yield, which results to residual settlement. This thesis provides a simplified numerical method implementation in finite element method (FEM) that estimates deformation of granular materials exposed to high numbers of cyclic loading for intricate 3D systems. Using explicit approach, which determines permanent strain for a specific number of loading cycles by means of empirical formulas in one solution step, this method eliminates error accumulation due to every FEM steps. Required experimental tests to obtain model parameters are elaborated. This model is utilized for the simulation of constant-amplitude cyclic loaded monopile embedded in soil. Comparison of numerical results with experimental data indicates great agreement and considerable improvement over commonly used existed methods. This study offers suggestions for prospective researches in the view of proposed method, which focus on 3D modeling of cyclic loaded granular materials. Furthermore, varying-amplitude cyclic loaded monopile is also modeled as an extension of the proposed model with strain-hardening approach.