Numerical Investigation of the Behavior of Pile Subjected to Uplift and Lateral forces

Abstract

The increasing complexity of modern infrastructure, such as skyscrapers and transmission towers, means that deep foundations need to be designed in a new way. These buildings put a lot of stress on pile foundations because they have both lateral and uplift forces acting on them at the same time. Current design codes, like (API, 2011) and (DNV, 2021), usually examine at these loading parts separately. This makes things simpler, but it can also lead to designs that aren't safe or materials that aren't used efficiently. This study fills this important gap by using a complex three-dimensional finite element analysis to look at how single bored concrete piles interact with each other when they are loaded in both the uplift and lateral directions in stratified cohesive soils, which are similar to those found in the Addis Ababa Bole sub city. Using PLAXIS 3D CONNECT Edition V21, a thorough parametric study was carried out to simulate a realistic four-layer soil profile using the Mohr Coulomb constitutive model. Using a range of loading scenarios, including pure uplift, pure lateral, and their combinations, the study methodically examined piles with different geometries (diameters: 0.6 m, 0.8 m, 1.0 m; lengths: 5 m, 10 m, 15 m). The accuracy of the numerical predictions has been verified by thoroughly validating the model against established field load test data. The findings clearly show that uplift and lateral loading mechanisms interact in a significant and negative way. Key findings show that concurrent uplift loads can increase lateral deflections at working loads by more than 25% and degrade lateral stiffness by up to 15%, while applying a lateral load equal to 75% of its pure capacity can decrease the uplift capacity by up to 12%. According to the study, shorter, stiffer piles have a more brittle failure mode and are disproportionately susceptible to these interaction effects. On the other hand, because of a deeper mobilization of soil resistance, longer, more flexible piles exhibit superior resilience. The development of useful, measurable design guidelines in the form of normalized interaction diagrams and capacity reduction factors is the main contribution of this study. With the use of these tools, practicing engineers can directly incorporate combined loading effects into pre-existing design frameworks. In order to improve pile foundations' safety, serviceability, and economic efficiency in quickly growing urban environments like Addis Ababa, this work firmly supports the incorporation of interaction analysis into standard geotechnical design practice.