Rate-dependent behaviour on lateral bearing capacity for caisson foundation under slow to rapid monotonic and cyclic loadings

This study investigates the rate-dependent nonlinear response of a soil-caisson system in dry, cohesionless Gifu sand under slow to rapid monotonic and cyclic lateral loading. The soil–structure interaction (SSI) effects are examined through experiments on a scaled model. Under monotonic loading, near-field pressure and acceleration responses are assessed, supported by Particle Image Velocimetry (PIV) on the ground surface. The results reveal that inertial forces primarily drive the rise in lateral bearing capacity before peak forces. However, beyond peak forces, all capacities converge regardless of loading rates. For cyclic loading, the nonlinear response is examined at slow, moderate, and rapid rates for target displacements up to the yield point, peak, and post-peak. The hysteretic damping ratio and near-field pressure responses are analysed to assess variations in global cyclic bearing capacity. A rise in bearing capacity is also observed under cyclic loading, influenced by both loading rate and displacement. It is found that at post-peak displacement, the cyclic bearing capacity exceeds that at peak due to repeated compaction. However, successive cycles cause a reduction in bearing capacity, reflecting the presence of local nonlinearities, such as soil separation from the caisson or loosening of neighbouring sand. The extent of these nonlinearities is found to be strongly influenced by the loading rate and the displacement. These findings provide useful insight for designing caisson foundations under dynamic loads.