ABSTRACT:

The stability conditions of the calcareous cliff of Corvara, in the Abruzzi Region (Italy), have been assessed on the basis of a rock mass characterization study and continuous/discontinuous modeling. Both the distinct element method (DEM) and the finite difference method (FDM) have been used for purpose of analysis. In both cases large scale instability phenomena have been evidenced with downward movement of the cliff and sliding along faults.

RESUME:

Les conditions de stabilite du richer calcite de Corvara, dans la region de I'Abruzzo (Italie), not tee evacuees sur la base de la characterization du massif ruche et sur la base de l'analyse numerique du type continue/discontinue. Les methods des differences finites (FDM) et des elements à block (DEM) not tee utilizes affine de matter à jour les phenomena's instability à grandee echelon, characterizes par des movements plan airs et Ie long des surfaces de discontinuity.

ZUSAMMENFASSUNG:

Die Stabilitat des Kalkfelsens von Corvara in Abruzzi (ltalien) wird mit Hilfe von Studien ueber die Charakterisierung der Felsmassen beurteilt sowie durch kontinuierliche/diskontinuierliche numerische Analysen. Angewendet wurden die Methode der finiten Differenzen und die Methode der distinkten Elemente, wodurch Phanomene von lnstabilitat in großem Maßstab bearbeitet werden konnten, die durch planare Gesamtverschiebungen und Verschiebungen lungs der diskontinuierlichen Oberflachen gekennzeichnet sind

1 INTRODUCTION

The calcareous promontory of Corvara, which extends for almost 4 km in the N-S direction and 500 m in width, is divided by a sub-vertical fault system that determines a stepped-line shape of the slope, with steep dipping walls and rock battlements (Figure 1). In the early 1900 the village, located on the northern corner of the massif, was declared unstable (Law no. 445/1908) and moved. From that time on, some limited toppling and falling of blocks occurred above the provincial and municipal roads. The Civil Engineering Department of the Abruzzi Region carried out a number of stabilisation works, mainly to prevent rock fall and to protect the roads. Barla et al. (1993) performed a geomechanical study with local stability evaluation and preliminary global analyses.

2 GEOLOGICAL DESCRIPTION

The rock mass is formed by calcarenite, micritic and bioclastic limestone with sub-horizontal bedding somewhere deformed and containing breccia. Rocks are heavily fractured by at least five main sets of discontinuity with average spacing of 0.10 to 1.70 m. The faulted zones are characterised by a cataclastic rock with a width of 1 to 2 m. Tectonic movements have caused the thrust of the calcareous mass on top of the sandy clay formation with chalk layers (Alanno's formation), which are subjected to a very slow gravitational deformation.

3 UDEC CODE DESCRIPTION

(Itasca, 1993) UDEC (Universal Distinct Element Code) is a two dimensional code developed by Cundall (1980). The model is an arrangement of rigid or deformable blocks which are able to interact through discontinuities. Block movements caused by disturbances (e.g., force, velocity) propagate into the blocky system until a static or dynamic equilibrium is reached. The solution scheme of the block equations of motion is an explicit finite difference method where calculations are performed as time steps. Deformable blocks are internally discretized in a grid with constant strain elements.

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