Modelling and Analysis of Soil-Foundation-Structure Interaction Under Dynamic Loading for Buildings in Soft Alluvial Soils of the Niger Delta

Buildings founded on the soft alluvial and deltaic deposits of the Niger Delta in the South South geopolitical zone are subjected to dynamic loading from industrial machinery, traffic, and low-level seismic ground motion that propagates uniquely through these highly compressible and high-damping soils. This study models and analyses soil-foundation-structure interaction under dynamic loading conditions representative of industrial facilities founded on soft alluvial soils in the Niger Delta, focusing on the amplification and modification of dynamic response relative to fixed-base assumptions. Finite element models of three- and six-storey reinforced concrete frames on raft foundations were developed using PLAXIS 3D, incorporating site-specific soil profiles from geotechnical investigations in Bayelsa and Delta States. Dynamic analyses were conducted for sinusoidal machine vibration loading and ambient traffic loading, with frequency sweeps performed to identify resonance risk. The influence of raft foundation size, soil layer depth, and soil stiffness on structural dynamic response was parametrically varied. Results indicate that soil-foundation-structure interaction effects increased fundamental period of the frame systems by 22 to 41 percent relative to fixed-base models, with the greatest elongation observed in the three-storey frame on the softest soil profile. This period elongation increased the spectral acceleration demand by up to 28 percent for the softer soil cases, contrary to common assumptions that foundation flexibility reduces structural response. Peak structural accelerations under machine vibration were amplified by a factor of 1.6 in soft soil cases relative to fixed-base predictions. The study recommends explicit soil-structure interaction modelling for all industrial facilities on Niger Delta alluvial deposits. Keywords: soil-structure interaction, dynamic loading, Niger Delta, soft alluvial soils, foundation.