Pile Group program for Full Material Modeling a Progressive Failure
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Strain wedge (SW) model formulation has been used, in previous work, to evaluate the response of a single pile or a group of piles (including its pile cap) in layered soils to lateral loading. The SW model approach provides appropriate prediction for the behavior of an isolated pile and pile group under lateral static loading in layered soil (sand and/or clay). The SW model analysis covers a wide range over the entire strain or deflection range that may be encow1tered in practice. The method allows development ofp-y cmves for the single pile based on soil-pile interaction by considering the effect of both soil and pile prope1iies (i.e. pile size, shape, bending stiffness, and pile head fixit<J condition) on the nature of the p-y curve. This study has extended the capability of the SW model in order to predict the response of a laterally loaded isolated pile and pile group considering the nonlinear behavior of pile material (steel and/or concrete) and its effect on the soil pile-interaction. The incorporation of the nonlinear behavior of pile material has a significant influence on the lateral response of the pile/shaft and its ultimate capacity. The reduction in pile lateral resistance due to degradation in the pile bending stiffness affects the nature of the accompanying p-y curves, and the distribution of lateral deflections and bending moment along the pile. Contrary to the traditional Matlock-Reese p-y curve that does not account to the variations in the pile bending stiffness, the modulus of subgrade reaction (i.e. the p-y curve) assessed based on the SW model is a function of the pile bending stiffaess. In addition, the ultimate value of soil-pile reaction on the p-y curve is governed by either the flow around failure of soil or the plastic hinge fonnation in the pile. The SW model analysis for a pile group has been modified in this study to assess the p-y curves for an individual pile in a pile group. The technique presented is more realistic and evaluates the vaiiations in the stress and strain (i.e. Young's modulus) in the soil around the pile in question due to the interference with the neighboring piles in a pile group in a mobilized fashion. The nonlinear behavior of pile material is also incorporated in the SW model analysis for a pile group.
Report No. CCEER 01-2