Hydrogeological Risk Analysis

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The Via Appia archaeological site is affected by an elevated hydrogeological risk due to active rockfall processes from the carbonate slopes flanking the route track, which are particularly evident south of the St. Andrea stronghold, towards Itri (Fig.1). More than 80 rock blocks were documented on the route, with a volume ranging from 0.5 to 1.5 m³ (Figs.2a,b). Structural analysis of the rock scarps evidenced potential unstable rock wedges of about 3.3. m³.

Gravity-driven processes causing instability have been simulated by a stochastic model and using software Rotomap® and RotoMap GIs®. Initial motion condition (free-fall phase) were constrained to the geomorphological characteristics of rock scarps (elevation, length etc). Motion along rock slope was modelled by adopting literature values for dynamic parameters such as normal and tangential restitution coefficients (Kn and Kt) and friction angle (Φd) which control the rebound and roto-translation phases, respectively. Calibration of dynamic parameters was set with a back-analysis procedure on modelling results and considering constraints from fallen rock blocks inventory.

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  Rock cliffs overhanging the Appia route track in the St. Andrea valley, from which rockfall events are possible.
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  Calcareous rock blocks arrested on the volcanic stone pavement after detachment and propagation along rock slope.
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  Calcareous rock blocks arrested on the volcanic stone pavement after detachment and propagation along rock slope.
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  GIS compatible 3D model of possible rock bock trajectories from rock scarps along the central sector of the study area (green lines stand for roto-translational motion, red lines for rebounds.
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  a) Map distribution of the specific kinetic energies (values are in m2/s2) for blocks detached from 10 meters-high rock scarps; b) map distribution of bouncing heights (m) gained during parabolic rebounds.
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  GIS compatible 3D model of the mitigation plane concerning the hydrogeological risk due to active rock fall processes along the Appia route between Fondi and Itri. Elastic barriers are dimensioned for different impact energies.

Simulations consider falling of a dimensionless rock blocks. For blocks detaching from 4,6 and 10 meters-high rock scarps, modelling result showed: the probabilistic distribution of possible trajectories; arrest points of rock blocks; the specific kinetic energies distribution (Fig.4a); the bouncing heights distribution (Fig.4b).

Finally, different design blocks were inferred and an hazard mitigation plane was defined which provides for placement and dimensioning of elastic barriers (Fig.5) capable to absorb impact energies between 2000 and 3000 KJ (considering design blocks of 1.56 and 3.32 m³, respectively).