Um estudo de caso de estacas metálicas envolvendo a retroanálise de tensões residuais de cravação

Abstract

This thesis gathered steel pile driving records with elements fabricated by Açominas. The soil profile is predominantly sandy. The piling records from the database were analyzed by quite different tools. The Danish dynamic formula is commonly used specially for controlling the foundation uniformity, according to the Brazilian standards. In spite of its simplicity, the Danish formula has provided very similar results to more elaborate wave equation analyses. Furthermore, while the wave equation considers the transmission of one dimensional longitudinal waves through piles, the actual phenomenon of pile driving into the soil mass is a three-dimensional problem. In fact, soil damping arises mainly by radiation or geometrical effect, dissipating the impact energy mainly through the soil mass. In order to consider in the analysis, the effect of residual stresses, not included directly in the Danish formula, the available database allowed the retro-analysis of pile deriving and its comparison by means of the three different calculation tools. Despite all the uncertainties inherent in some variables, as the efficiency of the driving equipment, soil damping and the loading function considered to reproduce the hammer impact as a necessary input for the FEM analyses, a comparison between the soil resistance during driving obtained through these three calculation tools has provided satisfactory results. The results indicated that notwithstanding the simplicity of the Danish formula, it was able to provide comparable results with much more refined methods. The difficulties inherent in a better representation of the soil as a necessary input to the wave equation and the 2D Plaxis FEM program, bring greater challenges in interpreting the results. The results from 2D Plaxis FEM program, in particular, shows the occurrence of residual stresses along the pile shaft and at pile toe. However, although most results of residual loads in pile shaft attained satisfactory results, some are not simple to explain. More advanced and detailed research need to be proceeded in order to better investigate and clarify some relevant behavior by means of instrumentation throughout the whole pile shaft since the beginning of the pile driving.