Effect of pile pitch variation on the uplift capacity using UTM apparatus

This article addresses the question of how the use of helical piles will improve the uplift capacity and displacement. Shahriar sand has been used with the relative density of 70% and the compression operation has been performed using hammering. The universal Zwick/Roell Z160 apparatus has been employed for tensile. With regard to the dimensions of the apparatus, the sand container was designed and physical modeling of the helical pile has carried out using dimensional analysis and nondimensionalization by Buckingham π theorem. After fabricating of the pile sample with pitch of 13, 20 and 25 mm, the behavior of simple and helical piles were investigated and the effect of pitch was examined. The maximum uplift capacity and its associated displacement were extracted and analyzed. The results show that the maximum uplift capacity of helical piles with pitch of 13, 20 and 25 mm in comparison with the simple pile increased 453.57%, 518.66% and 436.24%, respectively. When the ratio of the pitch/central shaft diameter is between 1 and 1.5, the tensile capacity is improved by the generated friction and the weight of sand on the blade as a resisting factor. By increasing the ratio of S/d to 1.92 the blade torsional angle increases and the sand weight on the blades decreases. Therefore, the uplift capacity is reduced compared to the previous two. The outputs show that the displacements of helical piles are approximately equal.