Experimental Work on the Effect of Under-reamed Pile Geometry on the Pullout Capacity of Sand

This work presents an experimental study that investigates the behavoir of both conventional and under-reamed piles embedded in a single layer of sand with varying relative densities and examines piles in different soil layers, subjected to pullout static monotonic loading. The study focuses on the influence of the spacing ratio between under-reams and the number of bulbs on the pile s ultimate pullout load. A uniform pile stem, a pile with a single bulb, and a pile with twin bulbs were the three varieties of small scale models of aluminum piles that were utilized. The pile s measurements were 25 mm in shaft diameter by 550 mm in height, with a 62.5 mm bulb diameter. To establish their impact on the uplift capability of an under-reamed pile in sand, the current work examines the location, spacing between bulbs, and the number of bulbs. At 35% relative density, the influence of various bulb spacing ratios S/Du is investigated (S/Du =1.0, S/Du = 1.25, S/Du = 1.5, S/Du = 1.75, and S/Du = 2). The test results revealed that the maximum ultimate pullout capacity is achieved when the bulb spacing ratio is S/Du =1.5. The pullout capacity increases 3.5 times for a single bulb and 7 times for a double bulb compared with a straight pile under the same condition, as well as an under-reamed pile in a dense or medium sand layer overlain by loose sand rises to a peak before capacity declines. Load-displacement curves and initial stiffness improve compared to homogeneous, loose, sandy soil.