Kinematic Interaction of Steel Pipe Sheet Pile Foundations for Floating Tip Conditions in Dry Sand

The influence of foundation tip condition on the kinematic responses of steel pipe sheet pile foundations was investigated through shake table experiments. A soil–foundation model was housed within a laminar shear box and subjected to horizontal harmonic base excitations under 1-g conditions. Effective foundation input motion and adjacent soil surface motion were recorded across a wide frequency range. The resonant frequency and maximum amplification of soil and foundation motion decreased with increasing vibration amplitude. For smaller input accelerations, foundation motion tracked free-field soil motion at smaller frequencies up to resonance, then remained lower than soil motion at higher frequencies. At larger input amplitudes, foundation top motion exceeded soil surface motion in the low-frequency zone. Comparison with fixed-tip foundation data revealed similar overall trends, driven by soil shear deformation. Floating-tip foundations exhibited higher effective foundation input motion at lower amplitudes, due to reduced filtering compared with fixed-tip foundations. At higher amplitudes, responses converged, while resonant frequency decreased for floating tips. Fixed tip conditions produced a stiffer soil–foundation system and a higher resonance frequency. These findings provided experimental evidence that foundation tip condition significantly altered kinematic interaction behavior and must be considered in sub-structuring methods for predicting structural response.