The tunnel Piscopio I is a twin-tube tunnel, 750 m long, included in the works of the Maxilotto 2 DG21/04 of the new highway SS 106 Jonica (Calabria, Southern Italy). During the excavation of the Piscopio I tunnel, several lacks in the Geological Model of Reference emerged. Above all, the discovery of a complex landslide along the left hydrographic side of the Alessi River, which interfered with the tunnel excavation. The slope movement was triggered when the tunnel excavation (from the opposite slope) crossed the watershed simultaneously with a significant pluviometric event (November 2011). Only an accurate analysis of the lithostratigraphic, structural and geomorphological settings of the area, integrated by a topographic and instrumental monitoring, had given the real dimension of the geometry and evolution of the landslide. In detail, the new acquired data allowed to identify: i) a new lithostratigraphic unit consisting of a clayey matrix with gypsum-arenites blocks; ii) a structural setting characterized by a main NO-SE normal fault, a NNE-SSO fault system, approximately aligned with the tunnel excavation direction, and at least other three secondary fault systems; iii) the main morphological elements of the landslide; iv) the evidences of the time variations of the Alessi Stream base level. Finally, we showed that the landslide predisposing factors are the high local relief, due to the ancient geomorphological setting, and the poor quality physico-mechanical characteristics of gypsum rocks, due to dissolution favored by the presence of water table, combined with a rainfall peak recorded during November 2011. Furthermore, the landslide composite movements are strongly influenced by the main faults and joints systems identified in the area. The revised Geological Model of Reference allowed us to evaluate the most appropriate systems for landslide stabilization (land taking back and deep drainage systems) and for tunnel consolidation and excavation (contour consolidation with unreinforced piles realized from the surface).

The tunnel Piscopio I is a twin-tube tunnel, 750 m long, included in the works of the Maxilotto 2 DG21/04 of the new highway SS 106 Jonica (Calabria, Southern Italy). During the excavation of the Piscopio I tunnel, several lacks in the Geological Model of Reference emerged. Above all, the discovery of a complex landslide along the left hydrographic side of the Alessi River, which interfered with the tunnel excavation. The slope movement was triggered when the tunnel excavation (from the opposite slope) crossed the watershed simultaneously with a significant pluviometric event (November 2011). Only an accurate analysis of the lithostratigraphic, structural and geomorphological settings of the area, integrated by a topographic and instrumental monitoring, had given the real dimension of the geometry and evolution of the landslide. In detail, the new acquired data allowed to identify: i) a new lithostratigraphic unit consisting of a clayey matrix with gypsum-arenites blocks; ii) a structural setting characterized by a main NO-SE normal fault, a NNE-SSO fault system, approximately aligned with the tunnel excavation direction, and at least other three secondary fault systems; iii) the main morphological elements of the landslide; iv) the evidences of the time variations of the Alessi Stream base level. Finally, we showed that the landslide predisposing factors are the high local relief, due to the ancient geomorphological setting, and the poor quality physico-mechanical characteristics of gypsum rocks, due to dissolution favored by the presence of water table, combined with a rainfall peak recorded during November 2011. Furthermore, the landslide composite movements are strongly influenced by the main faults and joints systems identified in the area. The revised Geological Model of Reference allowed us to evaluate the most appropriate systems for landslide stabilization (land taking back and deep drainage systems) and for tunnel consolidation and excavation (contour consolidation with unreinforced piles realized from the surface).