Advanced numerical modelling of deep-seated landslide effects on the Sparvo Tunnel using a time-dependent elastoviscoplastic soil model

This paper presents an overall assessment of the interaction between a deep-seated landslide and the Sparvo Tunnel, part of the A1 “Variante di Valico” motorway in Italy. The tunnel, excavated using mechanized TBM technology, consists of two parallel tubes with an exceptional external lining diameter of 15.0 m. The structure crosses a slope affected by a large Deep- Seated Gravitational Slope Deformation (DSGSD), characterized by a total mobilized volume of approximately 33 million m³. Autostrade per l’Italia S.p.A. commissioned Geosolving S.r.l. to assess possible evolution scenarios of the slope–tunnel interaction, with Tecne S.p.A. providing technical coordination and supervision. The study was supported by an extensive investigation and monitoring campaign carried out between 2014 and 2022. A multi-level modelling strategy was implemented, starting from 2D simulations and progressing to a detailed 3D analysis. The numerical models employed a time-dependent, non-linear elastoviscoplastic constitutive law (“SHELVIP”), specifically calibrated for the Palombini Clays formation using both laboratory results and long-term monitoring data. The results confirmed the significant influence of the DSGSD on the tunnel’s long-term behaviour and allowed the identification of the most affected tunnel sections where critical stress conditions are close to being critical. The study also demonstrated the effectiveness of advanced time-dependent constitutive models in reproducing the observed deformation trends. The outcomes highlight the need for continuous geotechnical and structural monitoring and for an Early Warning System (EWS), considered essential to ensure tunnel safety and support future risk mitigation strategies.