Numerical Study of Failure Mechanisms of Footings Subjected to Uplift and Lateral Loads Using PLAXIS 3D

The design of foundations for high-voltage electrical network lattice towers depends on reliable prediction of resistance to uplift and lateral forces. Because foundation works contribute substantially to the total project cost, a clear understanding of ultimate pullout capacity and the associated failure mechanism is required to support safe and economical design. This paper presents a three-dimensional finite element investigation using PLAXIS 3D to quantify the influence of soil type (pure sand and sand with 8% fines), footing dimensions ((3.5 × 7), (5 × 10), (7.5 × 15)), relative compaction RC are 92% and 100%, and embedment ratio (D/B = 1.0, 1.5, and 2.5) on the response of shallow horizontal footings. Two loading scenarios are considered: pure uplift and combined uplift-lateral loading. The results show that pullout resistance increases with footing size, compaction, and fines content; embedment ratio primarily increases capacity by mobilizing a larger soil wedge, while changes in the rupture geometry are most evident for the largest footing at the deepest embedment. Under combined loading, the vertical pullout capacity reduces relative to pure uplift for the investigated horizontal-to-vertical load ratio, highlighting the need to consider realistic multi-directional loading when interpreting failure mechanisms and estimating capacity. A comparison between laboratory model-test results and the PLAXIS 3D simulations confirms good agreement, with experimental measurements over-predicting numerical capacity by 8%, and with failure-plane inclination angles agreeing within 5%.