Behavior of axially loaded tapered pile groups using centrifuge test

The effect of tapered shaft on the performance of tapered pile groups under compression load has been investigated in this research. For this purpose, twelve axial compressive tests were conducted on groups of straight and tapered shaft piles installed in sand by using a geotechnical centrifuge. Three cross-section shapes of circular, square and X-shape cross sections for the pile groups were considered. The load–displacement behavior of X-shaped cross-section tapered and uniform (straight-side) single piles and also tapered and uniform pile groups is investigated for the first time. In each group, one pile was instrumented along its shaft to monitor the load transfer of the pile within the group. The results demonstrated that tapered pile group could tolerate at least 20% higher axial load than straight-sided shaft pile groups. Also, at least 35% higher initial stiffness was observed for a tapered pile group with 5D spacing compared to the uniform counterpart group. In addition, for a given group settlement, the straight shaft pile group transfers at least 9% greater load than the summation of loads carried by individual single piles within the same group, while in tapered pile groups, the load carried by the groups is almost equal to the summation of loads carried by individual piles within the same group. Tapered pile showed lower group efficiency compared to uniform piles. In addition, it is shown that tapering a pile enhances unit toe resistance as well as unit shaft resistance.