Role of Pile-Joint-Soil Interaction in Lateral Resistance: Finite Element Exploration of Steel Pipe Sheet Pile Foundations

Steel pipe sheet pile (SPSP) foundations, uniquely developed in Japan, consist of steel piles connected by joints, enhancing lateral resistance through a structurally interlocked system. While widely adopted as dual-use structures of cofferdams and foundations, the mechanics of these joints under lateral loading remain complex, and their effects are not fully understood. Despite the significance of the joint behavior, no existing numerical methodology accurately captures its mechanical response due to its high complexity under lateral loading. This study presents a numerical evaluation of the pile-joint-soil interaction in SPSP foundations, integrating computational methods with experimental verification. Our research group previously proposed a finite element modeling framework that effectively evaluates the joint behavior. In this study, the development and validation of the model are completed. Following this, the knowledge accumulated on this numerical methodology is integrated to systematically reproduce and extend the centrifuge test results, achieving high accuracy in simulating the joint behavior and soil-structure interaction. The findings reveal that variations in joint stiffness significantly affect lateral resistance, providing a uniquely structured methodology for optimizing the design of SPSP foundations. Additionally, numerical analysis indicates that the performance of laterally loaded SPSP foundations is highly dependent on the direction of the pile arrangement, which influences the corresponding joint internal force—a factor rarely explored for conventional grouped piles. These key findings provide insight into research topics that rely on joint-dependent evaluations. Beyond SPSP foundation applications, this framework offers a fundamental approach for development of more advanced grouped structure-foundation systems.