Behavior of under-reamed piles under inclined uplift loads in sand

Abstract Under-reamed piles are deep bored cast-in-situ concrete piles with single or multiple bulbs formed by enlarging the pile shaft. Such piles are best suited to soils with significant ground movement as a result of seasonal variations, filled up ground, soft soil layers, and loose sand. These piles also improve bearing and uplift capacities, as well as anchorage at greater depths. This paper aims to investigate and analyze the behavior of under-reamed piles under inclined tension loads, as well as to compare the results with regular piles. Single and double under-reamed piles with bulb diameter ratios of 2 and 3 were used as model piles. These piles were embedded in sand with relative densities of 30, 50, and 80%. The tension load was applied at zero eccentricity above the soil surface with inclination angles of 15º, 30º, 45º, 60º, 75º, and 90º with respect to the horizontal direction. The results indicated that the ultimate inclined tension capacity of the under-reamed pile increased as sand relative density, number of bulbs, and bulb diameter ratios increased. Furthermore, when the inclination load angle decreased, the ultimate tension capacity increased due to the generated passive earth pressure in front of the pile. The horizontal load component of the inclined load has more effect on the axial capacity; and this effect decreases with the increase in sand relative density. Finally, a theoretical equation was proposed to estimate the under-reamed pile’s ultimate inclined uplift capacity. This equation correlated well with the experimental results as R 2 = 0.91: 0.96.