ABSTRACT:

The slope deformation processes described in the paper, define a typical example of unstable behaviour for a tectonically active chain area in Italy, where slopes are formed of highly tectonized soils and rocks. Monitoring data compared to numerical modelling results show the existence of two interconnected mechanisms of deformation in the slope: a fast shallow mechanism (slump-earthflow) and a deeper and slower deformation process (deep-seated creep). This mechanism is fundamentally due to the poor mechanical properties of the deep soils, which are at yield and therefore undergo significant plastic deformations for even limited changes in loading.

INTRODUCTION

The present paper discusses the mechanisms of deformation active in an unstable slope, the Vadoncello slope, located beneath the town of Senerchia (Figure 1) in the upper Sele River Valley (southern Apennines, Italy), where the epicentre of the November 1980 earthquake (Ms=6.9) occurred. A landslide was activated on the Vadoncello slope on 29 December 1993. At its toe there is the Serra dell'Acquara landslide, a 2.5 km long slump-earthflow, which is quiescent at present but was mobilized by the 1980 earthquake, when also a subsidiary landslide was activated in the lower part of the Vadoncello slope (Cotecchia et al. 1986). No significant displacements have been observed on these slopes since the end of 1980 till December 1993, except for some slow retrogression of the rear scarp of the 1980 Vadoncello subsidiary landslide. The 1993 landslide developed as a slump at the top of the slope, with crown behind the 1980 rear scarp, and an earthflow downslope (Figure 1). Since this event ground movements have been active on the slope, which define a mechanism of deformation reconstructed by means of monitoring data compared to numerical modelling results, as discussed in the following.

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