ABSTRACT:

This paper describes the preliminary results of a study of large-scale movements affecting a slope in Northern Apennines, Italy. Slow movements of the slope have been detected since 1970 when two piers of a highway viaduct under construction began slightly to move. The displacements kept accumulating and eventually caused serious structural damage to the viaduct. Recently, the need of restoring the serviceability of the viaduct has raised the issue of predicting the slope evolution and defining appropriate remedial measures. The slope under examination consists of Cretaceous formations, mainly sandstones and marls, laying on highly fissured clay shales, dislocated and disarranged by an intense tectonic activity. Monitoring reveals that slow movements are developing along different shear surfaces at different depths. Site investigations and air photograph interpretation demonstrate that the instability mechanism which affects the slope can be described as a "complex landslide" made up of separate landslides. They originated in the last offshoot of an ancient mass movement but differentiated due to different lithological conditions and geological setting.

INTRODUCTION

Slow movements of a large slope in the Northern Apennines have been revealed by displacements of a highway viaduct. Since construction in 1976 two piers and the south-eastern abutment have been affected by significant displacements. Deformations of the structures were compensated by periodical repairs but eventually the accumulation of displacements caused serious structural damage, producing the closure of expansion joint among beams. Therefore, the need of restoring the serviceability of the viaduct gave the impulse for detailed studies to assess how the viaduct deformations are driven by instability mechanisms of the slope. Two main geotechnical investigations were undertaken in 1993 and in 1995. In 1995 a ground surface monitoring of a large area around the landslide initiated as well.

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