A Numerical Study of the Lateral Load-Sharing Mechanism of the Pile Cap in a 3 × 3 Pile Group

This numerical study utilizes a validated Plaxis 3D model calibrated against full-scale field tests to investigate the lateral load-sharing mechanism of the pile cap in a 3 × 3 pile group under horizontal loading. Numerical simulations calibrated against full-scale field tests reveal that the pile cap significantly enhances the lateral bearing capacity while reducing horizontal displacement by an average of 59.5%. The load-sharing ratio of the pile cap decreases from 62% at low loads to 50% at higher loads, with a corresponding increase in pile contributions. The decomposition of the pile cap’s resistance identifies passive earth pressure (PC-E) as the dominant component (72–80%), followed by base friction (PC-B, 15–18%) and side friction (PC-S, 5–12%). According to parametric analyses, increasing the embedment depth (H) from 0.5 m to 3.0 m elevates the pile cap’s load-sharing ratio by approximately 60%, while expanding the cap width (B) from 2.5 m to 3.5 m enhances lateral resistance by increasing the contact area. A power function relationship quantifies the load-sharing ratio (β) as a function of the product of H and B. These findings provide critical insights for optimizing pile cap geometry and improving the design of laterally loaded pile group foundations.