Seismic Response Analysis of Drilled Shafts in Dry Stratified Granular Soil

A three-dimensional discrete element method (DEM) framework was developed and applied to investigate the time-domain seismic response of a soil–pier system embedded in stratified dry sand. The numerical model was validated against analytical solutions to determine the ultimate vertical load capacity and internal forces when subjected to a lateral load at the pier head. Simulations were conducted to explore the influence of different excitation frequencies and amplitudes on soil–foundation interaction. Dynamic p–y curves were extracted at multiple elevations along the shaft to examine variations in lateral stiffness with depth. The results show that seismic loading significantly increases lateral displacement, and the residual response is strongly governed by the input motion amplitude. Peak lateral deformation and internal forces were observed when the excitation frequency coincided with the pier’s natural frequency. Both cyclic shear strain and ground settlement reached their maximum near the natural frequency of the soil deposit, and increased substantially with shaking amplitude.