Uplift Capacity of Under-Reamed Pile in Cohesionless Soil Underlaid by Cohesive Soil

Uplift capacity is a critical parameter in pile foundation design, particularly for piles that are subjected to vertical upward forces. Under-reamed piles are commonly employed for uplift resistance in various structures, including transmission towers, suspension bridges, tall chimneys, multi-story buildings, and offshore foundations. Extensive research has been conducted on the uplift capacity of under-reamed piles. Limited studies have been done on piles embedded in layered soil. Therefore, the current study deals with the uplift capacity of an under-reamed pile with a single bulb embedded fully in cohesionless soil and partially in cohesive soil. The uplift capacity is determined through a numerical analysis utilizing the finite element method (FEM). In the present analysis, the soil is assigned with the Mohr–Coulomb model, and the pile is assigned with the linear elastic model. The soil property of the clay layer is fixed, while the sand's friction angle (ϕ) is varied from 25 to 45°. Thickness of the top soil layer, i.e., sand, is also varied in the ratio of h/H = 0.25 and 0.5. The outcome of the present study includes load–displacement curves as well as displacement contours. The numerical analysis shows that the uplift capacity of the under-reamed pile increases significantly with the friction angle of the cohesionless layer, rising from 51.21 to 384.14kN as the angle increases from 25 to 45°. When the layer thickness ratio (h/H) is 0.25, the uplift capacity increases from 92.88 to 160.03kN, and at (h/H) = 0.5, it rises from 51.21 to 382.14kN.