ABSTRACT:

Two cases, of evolution of morphostructure of cliffs in soft rocks like tuff and calcarenite, respectively outcropping in the Cape of Posillipo in Campania and in the Agrigento town and Valley of Temples in Sicily, are analyzed on the basis of morphologic characteristics of the sites, mesostructural survey and mechanical characterisation of the lithotypes. The cultural and environmental heritage of these sites is heavily hastened by instability processes, due to the superposition of different lithotypes, the presence of discontinuities and differential erosion and deformation of bedrock. Both the rock masses are characterized by variability of the cohesion and the cementation, and well developed oriented structure. The theoretical analysis carried out with the FLAC code, evidences that some sets of subvertical discontinuities are consistent with the strained surfaces of the model and that they would be pertaining to morphological processes rather than tectonic events.

1 INTRODUCTION

Many historic locations in Italian landscape are characterised by high rock cliffs overlying steep soil slopes, affected by intense erosive processes that hasten dangerous rock failure phenomena and threaten the cultural heritage of the country, e.g. the Rock of S. Leo (Marche), and the Orvieto hill (Umbria). The two studied sites the Cape of Posillipo (Naples, Campania, Figure 1) and the town ofAgrigento (Sicily, Figure 2) and neighboring Valley of Temples, worldwide known by environmental and cultural value, are both endangered from a quick morphostructural evolution, due to superposition of layers of soft rocks on bed of grained soils. In this paper, the presence of vertical discontinuity parallel at the front of the slope affecting the soft rocks is justified, through numerical analysis. These discontinuities may be induced by the presence of soil bedrock more compressible. The analyses are carried out on simplified geometrical model with Flac 2D code (Itasca, 2000).

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