Numerical Investigation of Torsional Capacity in 2×2 Pile Groups in Soft Clay

Abstract

The application of eccentric lateral forces on supporting structures induces torsional loads on pile foundations, causing twisting at the pile head and significantly reducing axial capacity, which leads to increased foundation settlement. In this study, a three-dimensional finite element model was developed using ABAQUS CAE software to simulate the torsional behavior of a 2 × 2 pile group in soft clay. The piles and pile cap were modeled as linear elastic bodies, while the surrounding soil was modeled as an elastoplastic material using the Mohr-Coulomb failure criterion to capture nonlinear soil–pile interaction. The model incorporated boundary conditions, mesh discretization, and pile–soil interface characteristics to realistically represent field behavior. A detailed parametric study was carried out to examine the influence of pile spacing ( S / D ), length ( L / D ), and cap embedment conditions on torsional capacity. The results indicate that increasing pile length and spacing, or modifying pile cap embedment conditions, enhances the efficiency of the pile group under torsional loading. Specifically, as the S / D ratio increases from 2.67 to 4 and 5, the group torsional capacity increases by 14% and 28%, respectively. Similarly, increasing the L / D ratio from 25 to 30 and 40 improves torsional capacity by 7% and 19%, while cap embedment modification from e = – t (fully embedded) to e = 0 (ground level) and e = t (above ground) enhances capacity by 11% and 35%. These findings highlight the significant role of soil–pile–cap interaction in improving the torsional performance of pile groups in clayey soil.