Alberto Puccinelli

Fragility of Territory and Infrastructures Resulting from Rainstorms in Northern Tuscany (Italy)

In mountainous urbanized areas, shallow landslides cause significant, often unpredictable, hazard conditions. Landslides may involve and destroy infrastructures, kill people. Source areas are often located along the road network, representing a recurring situation also during not heavy rainstorms in Northern Tuscany. The landslides are generally first time debris slide-flows, occurring in peculiar environments: colluvium/debris slope cover (0.5–2 m thick), semipermeable-impermeable bedrock, hollow shaped slope, high slope gradient. Despite little size, they cause damage and deaths owing to their high velocity and erosion power. The source area along the road network is generally associated to the lack of efficient drainage systems. In fact, the concentration of uncontrolled runoff downslope creates an “unnatural” increase in pore pressure that the only rainfall should not have produced. This generates reaching and exceeding of the local critical rainfall threshold, making landslide hazard assessment more difficult. As example, in October 2010, almost 60 % of the landslides source area in the Massa area was located along the road network.

Estimation of soil properties of shallow landslide source areas by dynamic penetration tests: first outcomes from Northern Tuscany (Italy)

In Northern Tuscany (Italy) rapid, shallow landslides often cause casualties and severe damage. Aimed at contributing to the characterisation of the source areas of rapid, shallow landslides, this paper deals with the geotechnical parameterisation of the mainly involved soil by means of dynamic penetration tests. The source areas are usually located in difficult access sites, where boring and undisturbed sampling are very hard and onerous. Therefore, the results of 177 dynamic penetration tests were analysed, including dynamic probing (DP) tests and standard penetration tests (SPT). The results of these tests were related to relative density Dr and friction angle Φ′ of the soil by means of empirical equations. The distribution and variability of these parameters were analysed and related to soil type, test type and probing depth. The Dr and Φ′ values coming from the DP and SPT tests were found to be comparable. The Φ′ values coming from DP tests and direct shear tests showed an acceptable correlation, confirming the utility of the DP tests. The DP test can thus be an effective tool in the estimation of the properties of potentially unstable soil slope covers.RésuméDans la Toscane septentrionale (Italie) des glissements de terrain superficiels rapides provoquent assez souvent de considérables dégâts et de victimes. Ces glissements s’amorcent fréquemment dans les zones où le difficile accès ne permet pas de recueillir des échantillons intacts pour être testés en laboratoire. Ainsi pour la caractérisation géotechnique des terrains ont été utilisés les résultats de 177 tests de pénétration dynamique, ci-inclus les Dynamic Probing Tests (DP) et les Standard Penetration Tests (SPT). Du résultat de ces tests, par des corrélations empiriques ont été estimées les valeurs moyennes de la densité relative et l’angle de frottement du terrain étudié. Distribution et variabilité des résultats obtenus ont été analysées et corrélées avec le type de sol et le type et la profondeur de la preuve. L’étude a révélé que les valeurs moyennes de la densité relative et l’angle de frottement, obtenues par des tests DP, sont comparables à ceux obtenus à partir de SPT à la même profondeur. De plus, les angles de frottement, obtenues par de tests DP, montrent une bonne corrélation linéaire avec ceux déterminés par des essais de cisaillement directs réalisés en laboratoire sur des échantillons intacts. En conclusion, les comparaisons montrent que le pénétromètre dynamique continu peut être considéré comme un instrument utile pour l’estimation de certains paramètres géotechniques des sols en pentes potentiellement instables.

Zoning and Mapping Landslide Hazard in the Castelnuovo di Garfagnana Region (Tuscany, Italy)

ISPRA and Tuscany Region Administration recently funded a project aimed at assessing and mapping landslide hazard of the area of the n. 250 “Castelnuovo di Garfagnana” map (1:50,000 scale). The area includes the upper Serchio River basin (Tuscany, Italy) and exhibits peculiar geological and geomorphological features and severe climatic conditions, which cause high landslide hazard. The project proceeded as follows: 1:10,000 geomorphological survey and landslide inventory map; Physical and mechanical properties of rocks (discontinuities, strength, rock mass classification) and soils (grain size, consistency); GIS oriented organization of the spatial distribution of the considered factors; GIS supported statistical analysis (spatial analysis, conditional and multivariate analyses, neural network technique); Landslide hazard map, where landslide hazard is subdivided into five classes based on instability probability; Final products: landslide hazard map at 1:50,000 scale, together with other related maps (landslide map, structural sketch, geotechnical sketch, isohyet map, etc.); explaining booklet; database.

Processi gravitativi di instabilità in rocce molto fratturate: il metodo alle differenze finite in un caso applicativo nella provincia della Spezia

The Marinasco-Strà village is involved in wide instability phenomena in rock masses, determining a high landslide risk. In this area a geological-technical, kinematic and geomechanical characterization of the landslides and rock masses was carried out. Moreover, a monitoring system concurred in collecting important data on rainfall, piezometric response and deformation of the slopes. This integrated approach allowed the realization of a model of the landslide mass, regarded as a multiphase system and based on the physical-mechanical characterization of soil and rock. The determination of the state of stress and deformation and the location of actual or possible zones of failure inside the slope were among the main aims. In particular, the finite-difference method was applied, in order to estimate the stressstrain response of the slope to the variations of tensional state; in fact, this method fits better the instability phenomena in intensely fractured rock masses. A deformation model, consistent with the results of the investigations, was performed. In the analysed model, the shear strain concentrates along the main discontinuities deriving from plastic deformation of the mass causing the slope failure. Key terms: landslide, DGSD, numerical modelling, La Spezia, northern Apennine Termini chiave: frana, DGPV, modellazione numerica, La Spezia, Appennino Settentrionale

Approccio multidisciplinare per la valutazione della pericolosità di frana: indagini geologico-tecniche, idrogeologiche, geochimiche e isotopiche per la determinazione degli apporti idrici sotterranei nella frana di Cassana in Val di Magra (Massa-Carrara, Italia)

Cassana is placed in the Magra River Valley (Tuscany, Italy). A large and slow complex landslide involves the ancient village and causes severe damage and high risk. Many investigations were performed, aiming at gathering data and information and developing methodologies, in order to realize countermeasures and mitigate the risk. Geological and geomorphological investigations, subsurface exploration (core drillings, seismic refraction survey), geotechnical analysis, deformation and piezometer monitoring were carried out. Moreover, chemical and isotopic analyses on the underground waters were performed, aiming at identifying their intake areas and underground ways in the landslide bodies close to the village. The geochemical and isotopic investigations gave a meaningful contribution in reconstructing a geometric, kinematic and hydrogeological model of the Cassana landslide. This allowed the elaboration of a hypothetical outline of the underground water circulation and the individuation of some intake areas and preferential ways of the underground waters, greatly influencing the landslide and village instability. In conclusion, the geochemical and isotopic approach to the slope instability represents a possible and innovatory application of the chemical-isotopic technique in investigating the landslide causes. Key terms: Landslide, Geotechnics, Hydrogeology, Geochemistry, Isotope Termini chiave: Frana, Geotecnica, Idrogeologia, Geochimica, Isotopi.