Subsurface Weakness Amplification and Progressive Capacity Loss in Piled Port Structures under Repeated Operational Loading

Piled port structures experience repeated operational loading that may degrade soil–pile interaction and reduce foundation capacity over time. This study investigates subsurface weakness amplification and progressive capacity loss using three-dimensional finite element modelling of coastal soil profiles and pile systems under cyclic loading. Parametric analyses evaluated soil stiffness and loading variations to quantify degradation mechanisms. Results showed weak soil conditions caused 27.4% capacity reduction compared with 8.6% in stronger profiles, with strong correlation between soil degradation and capacity loss (R² = 0.87). The proposed Subsurface Weakness Amplification Index indicated a 3.2-fold increase in degradation sensitivity under weak subsurface conditions. This framework contributes to long-term reliability assessment of piled port structures subjected to repeated operational loading.