Comportamento à tração de estaca helicoidal instrumentada submetida a carregamento cíclico em solo arenoso

Abstract

Helical piles are foundations installed in the ground by means of torque to withstand of compression, traction and lateral loads. They offer advantages such as high productivity and installation with minimum noise and vibration. In this work, the pull-out behavior of instrumented helical piles subjected to cyclic loading in sandy soil is evaluated. The used pile had three bearing plates and was instrumented with electric resistance strain gauges in three sections along the shaft. Three pull-out load tests were performed: two with quasi-static cyclic loading and one with static loading, to verify the effects of cyclic loading. The tests with quasistatic loads were made with different values of average cyclic load and load amplitude. The results showed a great influence of the way in which the load increments were used, due to the densification and disturbance of the surrounding soil. The accumulated displacements tended to stabilize after the 10th cycle, low rates of mean displacement accumulation were not obtained and the number of cycles before failure showed to be dependent on the average load and the cyclic amplitude. The instrumented sections allowed to observe the reduction in the residual cyclic rigidity with the increase in depth along the shaft. The analysis of the mobilized loads in the bearing plates along the cycles, showed that the contribution to resistance from the lower bearing plate was responsible for most of the load capacity. It was observed that applied load levels and interaction factors between loading stages, which appear when the minimum load of a loading stage is lower than the maximum load of the previous stage, influenced the cyclical behavior of the soil-pile system by increasing the system rigidity and reducing corresponding displacements. Finally, the application of the quasi-static load cycles increased the static uplift capacity.