PSI - Issue 62

Luca Comegna et al. / Procedia Structural Integrity 62 (2024) 484–491 Luca Comegna/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Different mountainous areas of the Apennines chain (Italy) are frequently affected by failure mechanisms involving the widely outcropping structurally complex flysch formations. Even though the induced movements are usually slow, as a consequence of the rather low inclination of the involved slopes, their cumulative values are often large enough to damage structures, infrastructures, and lifelines (Lembo et al., 1998; Picarelli et al., 1999; Spinazzè et al., 1999; Sciotti and Calabresi, 2000; Boldini et al., 2002; Scarpelli et al., 2003; Picarelli and Russo, 2004; Vassallo et al., 2019; Desideri, 2021; Comegna and Picarelli, 2022). This paper aims to describe the main features of an instability event that affected for about 30 years a road embankment of the Italian A24 Rome-L'Aquila-Teramo highway (Fig. 1a) located along a portion of the Central Apennine chain between the towns of Roviano and Arsoli (Lazio Region). In particular, an about 70 m long section of the road surface on the slow lane towards L'Aquila began to fracture from the late '80s, thus requiring various targeted interventions over the years necessary to restore the design elevation. Different monitoring campaigns, carried out since 1998 (Fig. 1b, Table 1), highlighted the occurrence of a failure mechanism involving not only the road embankment but also the sloping foundation soils (Fig. 2a). Due to the observed seasonal variation of the displacement rate induced by the piezometric regime (Fig. 2b,c,d), a properly calibrated numerical model was developed to reconstruct the kinematics of the phenomenon accounting for the local hydrological balance. The latter has been derived by a climate database provided by the Italian Institute for Environmental Protection and Research (ISPRA), that allowed to extend assessments to time intervals not explored due to interruptions in monitoring activities.

Fig. 1. The case of Roviano: (a) study area (source: https://earth.google.com); (b) location of boreholes (modified after Comegna et al., 2023).

2. Geomorphology and climate data of the study area The study area includes a segment extending from kilometer 42+030 to kilometer 42+340 of the A24 highway located in the Sabini mountainous chain between the altitudes 562 m and 537 m a.s.l. of the steepest portion (15°-20° inclined) of the S. Elia mount. The latter in turn spans in the NW-SE direction from the altitude 966 m down to 317 m a.s.l., corresponding to the Aniene river valley. According to the local geological map (Chiarini et al., 2008), the basal parent formation consists of a Late-Middle Miocene marly-sandstone flysch, whose geomorphological evolution has been strongly influenced by various tectonic elements, such as fault planes, strike-slip faults, and overthrusts, which are typical features of structurally complex formations widespread throughout the Apennines (Esu, 1977). The basal formation is partially covered in the investigated area by an about 8 m thick debris originated by a Late Pleistocene-Holocene alluvial cone. The road embankment, featuring a maximum thickness of 16 m, an average slope angle of 28°, and a width of 30 m, is founded