Numerical Investigation of Pullout Capacity of Under-Reamed Piles in Clayey Soils

Husam M Saleh¹Maher M Jebur²Adnan Q Mohammed²Mahdi Karkush³Mohanad M Sabri^4*

• ¹National Center for Engineering Consultations, Baghdad, Iraq
• ²Department of Reconstruction and Projects, University of Baghdad, Baghdad, Iraq
• ³Department of Civil Engineering, University of Baghdad, Baghdad, Iraq, Baghdad, Baghdad, Iraq
• ⁴Peter the Great St.Petersburg Polytechnic University, Saint Petersburg, Russia

Under-Reamed Piles (URP) are a type of concrete bored pile featuring bulbs along the stem. Despite their use, the behavior of these piles, particularly under pullout conditions, remains insufficiently understood. This study employs three-dimensional Finite Element Method (FEM) to numerically analyze the response of URPs in clayey soils of various stiffness and subjected to pullout forces. Soil properties obtained from field tests were utilized as input data in the analyses. Various bulb positions along the pile stem length, L (i.e., 0.25L, 0.5L, 0.75L, and L), were modeled to evaluate the effect of bulb location on the pullout capacity of URPs in homogeneous clayey soil. The results of the proposed numerical model were compared with the pullout capacity of conventional straight-shaft piles (without bulbs). The findings revealed that the presence of bulbs significantly reduced vertical displacement for all bulb positions. Additionally, the study showed that the URP and surrounding soil interacted most effectively when the bulb was positioned at 0.75L. The pullout capacity of piles increased by approximately 60, 100, 125, and 81% compared to straight-shaft piles when the bulb was placed at 0.25L, 0.5L, 0.75L, and L, respectively, in medium stiff clayey soil. Additionally, a notable improvement in the pullout capacity of the under-reamed piles (URP) was observed with an increase in the stiffness of the clayey soil. Overall, the study emphasizes the benefits of double under-reamed piles in enhancing the pullout capacity of pile foundations.