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Abstract: The Apennine mountains of the Parma Province (Italy) are characterized by a young geological structure subjected to continuous morphological modification in many areas. As a consequence, several active landslides can be identified in this region. Among others, slow movements occurring over large areas are the typical type of instability in this zone. The slow but constant deformation process can induce major damage when interacting with major civil infrastructures such as bridges, roads and railways, but has a less severe effect on agricultural practice and smaller structures. Four different slope instability phenomena are analyzed in this paper. All the slopes are characterized by similar geological and hydrogeological features and by similar deformation rates. All slopes have been studied by means of experimental tests and numerical modelling in order to understand the failure mechanism and the evolution of slope movement. The deformation of each slope was monitored using superficial topographic control points and inclinometers, while its water level regime is controlled by means of discontinuous piezometric readings. The monitoring results, together with in-situ and laboratory testing, allowed a more detailed understanding of processes such as deformation under a constant active stress. The development of a numerical model was necessary to predict creep rates. Special attention has been given to the mineralogical components of the material involved in the unstable areas, in order to identify the material structure characterizing these types of landslides. This work is aimed to be a methodological study of a type of complex phenomena that are recurrent in a zone of the Apennines. These phenomena can be partly considered as mudslides acting in undrained loading condition along localized shear zones but creep gives a fundamental contribution to mass deformation that must also be considered in the phenomenon modelling to be able to obtain measured displacement rates. For this purpose creep tests have been performed in undrained conditions and modeled by a finite difference code for the calibration of relevant material mechanical parameters. The paper reports the description of the problems encountered to sample and to make experimentation on this kind of complex materials along with the obtained results and, at the end, gives some operative suggestions on how to overcome such difficulties. [Copyright &y& Elsevier]

Landslide dams are a particular kind of natural dam which forms when an earth or rock mass reaches a river channel causing its complete or partial blockage. Since 1995, the Earth Sciences Department of the University of Firenze has been running a project involving the inventory of landslide dams in the Northern Apennines, which currently contains more than 60 case studies. It is known that the geotechnical characterisation of landslide dams is closely related to the grain size distribution of the materials composing the dams. In particular, grain size exerts a control on dam stability, influencing the strength and the permeability of the dam material. The main purpose of this work is to contribute to grain size characterisation of landslide dams by giving an outline of the possible methods that can be used for grain size assessment and showing the results obtained from the case studies selected in the Northern Apennines. Indeed, despite its importance, there are few quantitative studies directed at determining grain size distribution of debris dams, mainly because customary bulk sieve analyses are impractical when dealing with materials often ranging in size from blocks tens of cubic metres in size, to microscopic particles. This paper presents results derived from the application of two main sampling methods on 42 landslide dams, (a) volumetric analysis and (b) grid by number analysis (here presented in two variants). These techniques allow us to obtain very similar grain size distributions for the coarser part of the debris material, while some differences persist for the finer fraction. The paper would also like to highlight the importance of getting accurate grain size data, with particular reference to the determination of the hydrograph derived from a landslide dam failure. Many deterministic models attempt to approach this problem, by taking into account only the median percentile (D50) of the cumulate grain size distribution. However, in most of the selected cases, a marked bimodal distribution was found in the frequency diagrams, so the fiftieth percentile (D50) is often one of the less representative grain size classes. It should thus be taken carefully into account that this choice could be misleading, as it is not necessarily justified by the physical evidence. [Copyright &y& Elsevier]

Abstract: This paper describes the geometrical structure and the main kinematic features of an ancient and active landslide which develops in structurally complex formations of the Southern Apennines (Italy): a scaly clayey formation in the medium and lower part of the slope, and a stratified marly–calcareous rock formation in the upper part. The landslide 3D geometry was reconstructed by using topographic data, stratigraphies from continuous coring boreholes and inclinometer data. The analysis of the kinematic features was based on the measurement of deep and superficial displacements. Laboratory tests were carried out to evaluate shear strength parameters. It was found that in each investigated transversal section of the landslide channel the displacements can be considered uniform, and that the decrease of the displacement rates, from upslope to downslope, mostly depends on the increase in the areas of transversal sections, the “soil discharge” variations being slight. Stability analyses confirmed that shear strength close to the residual value is available on the slip surface. The large difference between residual strength and peak strength of the landslide material is consistent with the displacement uniformity. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to analyze the reactivation mechanism of ancient earth flows, with a view to gleaning information that can subsequently be utilized to formulate a risk-reduction strategy. All considerations made herein are the result of direct experience and observation of actual events which have occurred over the past few decades in the Northern Apennines. Particular attention has been paid to the analysis of the evolution of landslides during actual reactivation, acknowledging a typical, recurring succession of events that precede the failure of the slope. The hazard assessment of these large landslide bodies, which are of slope scale, constitutes a thorny problem, especially in view of the inapplicability of traditional deterministic models such as limit equilibrium stability analysis. Nevertheless, a site-specific assessment of probability of reactivation of these large and ancient earth flows is fundamental to effective land-use planning. [Copyright &y& Elsevier]

The paper discusses the results of an engineering-geology study of an area in central Italy affected by complex gravity induced slope instability. A finite-difference analysis was implemented to demonstrate that stratigraphy and recent tectonics have had a crucial impact on the gravitational processes that have occurred in a built-up area of the central Apennines (Italy). The creation of a reliable geological-evolutionary model proved to be a key tool for subsequent development of a numerical model, capable of elucidating the main factors and parameters controlling slope instabilities.The study area, in the vicinity of the small mountain village of Micigliano (central Apennines), displays extensive outcrops of carbonate platform lithotypes, hemipelagic marly-clayey deposits and arenaceous pelitic turbidites. Its tectonic setting is very complex, with intense faulting (thrusts, normal faults, and complex kinematic faults) and folding. A geological-evolutionary model of the instability processes in the various sectors of the study area was formulated and fine tuned, on the basis of detailed geological and engineering-geology surveys, assumptions on the mechanical and hydraulic characters of the local geological bodies, and observation of the morpho-evolutionary processes. Subsequently, a stress–strain analysis was applied to the model, using the finite-difference method, in order to reconstruct the complex mechanisms governing evolution of the various sectors of the investigated slopes and the effects of gravity-caused instability on the exposed lithotypes.The numerical model also helped to validate the consistency of the stress–strain assumptions with the deformation mechanisms observed in the various investigated sectors of the study area, yielding a kinematic picture of the causal factors of the local gravity-caused instability in space and time. [Copyright &y& Elsevier]