Influence of loading intensity on the vertical dynamic impedance of inclined pile groups in cohesionless soil

Characterising the dynamic impedance of piled foundations is critical for seismic design, yet the performance of inclined piles remains a subject of debate. The influence of pile inclination on frequency-dependent stiffness and damping, as well as the effects of loading intensity on these impedance characteristics, requires further understanding for group configurations. Moreover, while loading-intensity-dependent impedance behaviour has been reported for vertical pile groups, its applicability to inclined pile groups requires further investigation. Therefore, this study addresses these queries by determining the stiffness and damping characteristics of floating inclined pile groups embedded in cohesionless soil using three-dimensional finite element-based simulations. A 3 × 3 pile group with 5° and 10° inclinations is analysed to determine the impedance characteristics under harmonic pile-head loading. The numerical framework for impedance analysis is validated against experimental results for single piles at 0°, 5°, and 10° inclinations and for a 0° 3 × 3 pile group. It is then extended to the 5° and 10° group configurations, for which no experimental data are available. The results demonstrate a distinct behaviour between single piles and pile groups in relation to pile inclination. In the case of single piles, an increase in inclination results in a reduction of pile head stiffness, attributed to the combined lateral and vertical displacements induced by vertical loads. However, for pile groups, the effect of pile-to-pile interaction generally diminishes with increasing inclination, although the magnitude of this reduction depends on excitation frequency, inclination angle, and receiver pile location. This reduction arises from changes in wave scattering and stress transfer associated with depth-variable pile separation when receiver pile stiffness is accounted for. As a result, the investigated inclined pile groups exhibit enhanced pile-head stiffness compared with the vertical pile group under the considered loading conditions.