Under-reamed piles are a type of deep foundation with enlarged bulbous shapes at intervals along their length and are used to support structures in areas with weak or expansive soils. Under-reamed piles are used in machine foundations, foundations for offshore structures, and transmission towers where both lateral and vertical loads are imposed. This study aims to determine the failure mechanism of different pile geometry under the action of axial compressive load. Straight shaft piles and single and double under-reamed piles are chosen in the present study. The present research selects 5 m and 6 m pile lengths for both straight shaft and under-reamed piles with a stem diameter of 0.50 m. The bulb diameter of the under-reamed pile is taken as 1.25 m. In the present numerical study, PLAXIS 3D software has been used to study the load-settlement behaviour of straight shaft piles, under-reamed piles, and groups of straight shaft and under-reamed piles in sand. The result shows that the settlement of 5 m length piles is more than 6 m length piles. The settlement of the under-reamed pile decreases with the increase in number of bulbs. The present numerical analysis results will be highly beneficial in locations where the seabed consists of soft or weak soils that require a larger bearing area to provide sufficient stability.