Um estudo de caso envolvendo a retroanálise de tensões residuais de cravação.

Abstract

Residual driving stresses occur when both pile and soil are not fully decompressed after complete dissipation of the energy transferred to the pile during its installation. This subject is receiving increasing attention from many researchers, since the presence of residual stresses along the pile cause a change in its behavior when it s loaded. This thesis includes earlier studies that established the key factors which affect the residual driving stresses. Some parametric simulations have been tentatively run aiming to better understand the development of residual stresses with tip resistance percentage, as a complement of previous analyses from Costa (1994). Costa (1994) noted that the tip resistance percentage is a relevant factor in the evaluation of residual driving stresses. It has also been observed that the ratio between the tip residual load and the global bearing capacity increases with increasing tip percentage, reaching a maximum value and then presenting a decreasing behavior. This behavior is similar to the soil compaction curve, where the specific gravity increases when the water content is also increased, until it reaches a maximum value, corresponding to the optimal water content, and then it decreases. It was also verified that, similar to the increase of compaction energy which translates the curve upwards and to the left of the water content x specific gravity graph, increasing the length of the pile produces a similar behavior. Finally, a case history with favorable conditions for the development of high residual driving stresses has been selected for the main analysis. The thesis analyze a well-documented case history involving long steel piles embedded into a young residual soil, with high bearing capacity and extensive documentation. The back-analysis of five piles databases showed that the expected residual loads calculated by means of a wave equation program were very close to the experimental values. It was also observed that the depth of the neutral plane calculated by the program showed an excellent agreement with that observed experimentally. The most important result of this research arose when the tip percentages values were introduced in the x-axis and the values of the ratio tip residual load and global bearing capacity, in the y-axis. A curve very similar to a compaction curve was observed. This thesis demonstrates to be possible and simple to predict residual driving stresses by analyzing the wave equation.