PSI - Issue 84

Lorenzo Di Taranto et al. / Procedia Structural Integrity 84 (2026) 1007–1014

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a relevant kinematic reactivation coinciding with the severe rainfall events that occurred in the immediately preceding period, likely influencing the equilibrium of the structure-foundation system. Consequently, the high temporal congruence observed between deep-seated gravitational movements and the structural response confirms that the interaction between the slope instability and the Santo Stefano Viaduct is characterized by a direct kinematic transfer from the deep-seated movement to the bridge. 3. Interpretation of the observed phenomenon: The integrated analysis of geological, geomorphological, and instrumental data allows for the definition of the phenomenon affecting the 'Santo Stefano' Viaduct slope as a slow-moving gravitational deformation characterized by a multiple roto-translational sliding kinematic mechanism. The reconstruction based on high-resolution LiDAR surveys and direct investigations highlights a system of active slip surfaces developing at various depths within the Subapennine Clays Formation.

Fig.7. Cross-sections of slow-moving instability phenomena based on high-resolution LiDAR surveys 1 meter in the area surrounding the 'Santo Stefano' Viaduct. The image integrates the chorographic context of the site (top left) with the reconstruction of the deformation mechanisms affecting the geological profile, where the green line indicates the primary sliding surface identified at a depth of approximately 30 meters and the red lines represent the deeper-seated kinematic processes associated with Deep-Seated Gravitational Slope Deformations (DSGSD). The primary deformational mechanism is located at a depth between 25 and 30 meters, where inclinometer data recorded cumulative displacements of up to 18 mm over the last year. A shallower kinematic process, identified at approximately 10 meters below ground level (b.g.l.), is superimposed on the primary mechanism. This superposition indicates the structural complexity of the landslide body, which involves multiple stratigraphic horizons (Fig. 7). The identification of specific dynamic processes, characterized by an apparent regression in measured deformations, supports the hypothesis of a deeper instability zone associated with Deep-Seated Gravitational Slope Deformations (DSGSD). This interpretation is further corroborated by historical inclinometer data from previous monitoring campaigns, which revealed deeper-seated kinematic processes exhibiting similar regressive displacement trends over time. Such complex behavior underscores the structural heterogeneity of the landslide body, suggesting that the deformation involves multiple stratigraphic horizons and reflects a long-term evolutionary trend of the slope. 4. Conclusions: The case study of the 'Santo Stefano' viaduct highlights the complex interaction between major infrastructure and slow-moving gravitational deformation phenomena, providing a detailed framework of a phenomenology