The runout of dry blocky rock avalanches produced by planar rockslides affecting a limestone formation with clayey interbeds is analysed by means of distinct element modelling. Numerical analyses are validated by means of the back analysis of a historical rockslide occurred in the investigated area and physical aspects of the phenomenon evidenced by modelling are discussed.

On analyse par la methode aux elements distincts la distance de parcours des avalanches rocheuses sèches produites par des glissements plan interessant une formation de calcaire à intercalaires argilleux. Les analyses numeriques sont validees à l'aide de la back-analysis d'un glissement historique survenue dans le site en examen. On decrit les aspects physiques su phenomène mis en evidence par la modelisation effectuee.

In diesem Beitrag wird die Reichweite von Steinlawinen besthend aus trockenem blockhaftem Fels mittels der Distinct Element Methode untersucht. Die Steinlawinen werden erzeugt von Rutschungen in einer Kalkstein-Formation mit tonhaltige Schichten betreffen. Die numerischen Berechnungen wurden anhand einer Simulation einer historischen Bergsturzen verifiziert, der sich auf den untersuchten Gebiet ereignete. Auf der Basis der erhaltenen Ergebnisse wurden die physikalischen Aspekte der untersuchten Steinlawinen analysiert.

Introduction

Since the last deglaciation of the South-Eastern Alpine arc, destructive movements have frequently been produced by large planar rock slides along homoclinal slopes formed by regularly stratified limestones with clayey-marly interbeds.

The left flank of the Adige River valley represents a typical area where, during historical times, rock slides have produced huge rock avalanches, which discharged tens of millions of m3 of debris into the Adige River Plain, diverting the river bed some 500 m away from its original course (figure 1).

Since the slope overlooks the industrial estate of Rovereto as well as the motorway and railway to Austria, the evaluation of the reach of potential avalanches is instrumental for risk assessment or mitigation.

Geological setting of the study area

The landslide area extends over the whole left flank of the Adige River valley, south of Rovereto. The valley flank is carved into a large NW dipping homocline formed by the lower-middle units of the Calcari Grigi limestone formation. From bottom to top three units can be identified:

  • 0.1 to 1 m thick calcarenite and micritic limestone layers separated by clayey-marly interbeds whose thickness ranges from a few millimetres to some centimetres;

  • nodular limestone layers from 0.1 to 0.5 meters thick, which are separated by thin clayey-marly interbeds;

  • oolitic limestone layers up to 4 m thick without interbeds.

(Figure in full paper)

The limestone layers have an average dip of 22° towards the valley with local variations (figure 2). They are sound, scarcely fractured and exceptionally continuous as well as the clayey-marly interbeds are.

The homocline is divided into relatively regular and unfolded blocks by major NNW-SSE strike slip faults. The rock is cut in slabs by a set of joints parallel to the fault system and by closed and widely spaced N20W and N80E trending fractures. No shear strength is mobilized along fractures due to their orientation with respect to bedding.

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