Influência do modelo de transferência de carga de estacas isoladas na previsão do seu comportamento

Abstract

The settlement estimation of a single pile or pile group is very relevant in soil-structure interaction analyzes. The ABNT NBR 6122 (2010) establishes, in its section 5.5, that "In structures where the deformability of foundations can influence the load distribution, the interaction between soil-structure or foundation-structure should be studied".For this reason, the accurate estimation of settlements has deserved the attention of many geotechnical designers. However, unlike shallow foundations that transmit the entire structure load through stresses at its bases, the deep foundations transmit part of the load by lateral friction and part by the tip. In this case, the load transfer form to the ground should be considered, since the portion of resistance corresponding to the lateral friction could be all gone for the service load.The percentage of load transferred by the tip in the service situation is much lower than the one that occurs at the rupture time.Before reaching this stage (ultimate or rupture), for example, at the level of service loads, the mobilization of resistance is partial and most of the ground surrounding the pile is far from rupture.The way the load applied to the top of a pile is distributed along the shaft depends not only on the soil stratigraphy but also on the relative stiffness between the pile and the ground.The behavior of the foundation expressed by the load-settlement curve is also a function of the load transfer, which is the way the load applied at the top is distributed in depth. This is usually considered in a simplified way, since its determination involves many uncertainties, being a function of the applied stress level, also varying with time, among other factors. In this dissertation, some single pile cases with known behaviorwere studied. The settlements are predicted with estimated load transfer in a simplified way and by using load-transfer functions with models available in the literature. This research aims to take a critical look at the models available for evaluating the mechanisms of load transfer of single piles, in order to verify its influence in the prediction of the load-settlement behaviorand to compare these with the load test results.The results showed that the use of simple models of analysis of settlement, as well as the consideration of load transfer in a simplified way, generated good predictions of the load-settlement behavior for the cases analyzed, when compared to the results of the instrumentations.Finally, it was also verified the influence of the residual stresses, whose effect is to make the load-settlement behavior more rigid, not influencing the ultimate load.