Investigation of tunnel–soil–structure interaction under dynamic loading in non-homogeneous soils: case study of Catania, Sicily, Italy

This study investigates the seismic response of tunnel–soil–structure systems within the context of sustainable urban infrastructure, where underground tunnels play a key role in reducing traffic congestion and environmental impact. While previous research has extensively examined tunnel–soil interaction under seismic loading, the combined influence of soil heterogeneity and the dynamic interaction between underground tunnels and aboveground structures remains insufficiently explored. Since these interaction mechanisms depend on the characteristics of the coupled system, their relevance cannot be assessed a priori without an explicit analysis of the tunnel–soil–structure response. To address this issue, the present study employs a fully coupled two-dimensional finite element approach to investigate the seismic response of a tunnel, heterogeneous soil, and an aboveground building considered as a single interacting system. The analyses are based on a representative cross-section of the Catania metro network (Italy), supported by a geotechnical characterization that enables a realistic representation of the local stratigraphy. A series of numerical analyses is performed by varying tunnel cover depth, building position, and seismic input to investigate their effects on tunnel lining forces, peak ground accelerations, spectral accelerations, and the response of the aboveground structure. In parallel, the applicability of the classical analytical solutions proposed by Wang (1993) and Penzien (2000), originally developed for homogeneous soils, is investigated under stratified ground conditions through a practical adaptation aimed at providing a complementary engineering assessment of tunnel lining forces. The results provide insight into the physical factors governing the significance of tunnel–building interaction in heterogeneous ground conditions and highlight the configuration-dependent nature of the seismic response of coupled tunnel–soil–structure systems.