Investigation of monotonic behavior of different-pattern helical pile groups in sandy soils

Abstract Nowadays, due to the rapid progress of countries in constructing various structures, cost and the environment have become highly important. These structures must be considerably strengthened and improved, as they are built on land and water. Helical piles are among the most appealing and popular techniques for enhancing problematic soils. In these piles, a central steel shaft is welded to one or more circular plates (helixes) inserted downward into the ground to simultaneously provide torque and force. Nonetheless, the evaluation of the bearing capacity and performance of these piles remains a novel and complicated concept, particularly when they are used in different-pattern pile groups under compressive and tensile loads. This study presents the results of the physical modeling of 1-g scaled helical pile groups in dry sand with various relative densities (Rd). The outstanding feature of this research is that it analyzes the influence of changes in soil Rd and pile arrangement on group behavior. These tests have been designed in two types: single-helix and double-helix piles with two, three, and four arrangements. The first two groups are in a linear form, while the last one is in a plus shape. The results revealed that in loose sand, increasing the Rd of the soil had the highest effect on the bearing capacity of different groups compared to other variables. On average, in dense sand, adding piles had the greatest impact on increasing the bearing capacity of various pile groups. In all cases, the compressive capacity of the pile groups was extremely higher than their tensile capacity. Additionally, the ultimate bearing capacity of the pile increased by almost 11% after increasing the spacing between the piles. Graphical Abstract