One Health-relevant ground-movement risks from chemically weakened urban surface soils during deep excavations: a 3D...

Urban surface soils in rapidly urbanizing areas are increasingly affected by chemical inputs such as acid rain, industrial effluents, and deicing salts. These factors may accelerate chemical deterioration and cause coupled reductions in stiffness and shear strength, thereby altering excavation-induced ground deformation and the response of support systems in densely built environments. In this study, a typical rectangular deep excavation is investigated using three-dimensional finite-element analysis. Two degradation-sensitive parameters of the surface layer, the modulus ratio (E₁/E₂) and the internal friction angle (φ), are systematically varied. Their effects are evaluated using four deformation indicators: maximum surface settlement, settlement trough width, maximum retaining wall displacement, and maximum column settlement. The results indicate that maintaining E₁/E₂ within 0.4-0.6 while limiting the reduction in φ to no more than 2° provides a more favorable balance between peak deformation control and spatial diffusion. Under severe deterioration (E₁/E₂ < 0.3 and φ reduction >3°), excavation-induced responses become markedly more adverse. These findings provide a basis for design-stage screening that jointly considers stiffness-related and shear-related deterioration of chemically affected surface soils, and offer reference for risk assessment of deep excavations in urban environments.