Federica Cotecchia

Deterministic Landslide Hazard Assessment at Regional Scale

The paper presents a new methodology for the deterministic assessment of landslide hazard at the regional scale in geologically complex chain areas. The methodology entails site specific geo-mechanical studies, as background of any hazard prediction application, and the creation of a Regional Landslide Manual portraying the geo-mechanical knowledge about the slope conditions across the region. The search in the regional manual of the landslide mechanisms which may correspond to the combination of landslide factors recorded at the local scale results in the hazard prediction. The testing of the methodology in the Daunia Apennines is discussed.

Slope instability processes in intensely fissured clays: case histories in the Southern Apennines

In slopes formed by tectonized clayey turbidites, the soil fissuring recurrently influences the hydro-mechanical soil properties, determining an impoverishment in strength and an increase in permeability of the slope that make them predisposing factors of landsliding. This paper presents three case histories of slopes within tectonized clayey turbidites that are representative of several others in the Southern Apennines and, more widely, in the southern Mediterranean. The paper reports a novel attempt to connect tightly the slope geomorphological and hydro-mechanical features to the slope geological history, through an introductory presentation of the geological setting and history of the chain where the slopes occur. The slopes, location of very slow landslides, have been reconstructed based upon field surveys and investigations, multi-aerial photo-interpretation, laboratory testing, monitoring and numerical modelling. Furthermore, novel is the attempt to present, all together, the behaviour of the soils involved in the three landslide case studies, in the light of the mechanical modelling approach to fissured clays recently presented in the literature.

Numerical modelling of slope–vegetation–atmosphere interaction: An overview

The behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and by soil–vegetation–atmosphere interaction. Porewater pressure changes within a slope related to variable meteorological settings have been shown to be able to induce soil erosion, shrinkage–swelling and cracking, thus leading to an overall decrease of the available soil strength with depth and, ultimately, to a progressive slope collapse. In terms of numerical modelling, the stability analysis of partially saturated slopes is a complex problem and a wide range of approaches from simple limit equilibrium solutions to advanced numerical analyses have been proposed in the literature. The more advanced approaches, although more rigorous, require input data such as the soil water retention curve and the hydraulic conductivity function, which are difficult to obtain in some cases. The quantification of the effects of future climate scenarios represents an additional challenge in forecasting slope–atmosphere interaction processes. This paper presents a review of real and ideal case histories regarding the numerical analysis of natural and artificial slopes subjected to different types of climatic perturbations. The limits and benefits of the different numerical approaches adopted are discussed and some general modelling recommendations are addressed.

The Influence of Meso-Structure on the Mechanical Behaviour of a Marly Clay from Low to High Strains

On October 31, 2002, a ML=5.5 earthquake struck the Molise region in Southern Italy. The strongly non-uniform damage distribution observed in the town of San Giuliano di Puglia suggested that site amplification significantly affected the seismic response of the Toppo Capuana marly clay formation.

From a phenomenological to a geomechanical approach to landslide hazard analysis

The diagnosis of landsliding at the slope scale resulted from synergic geohydromechanical analyses of the slope factors, which should represent the first step to assess landslide hazard. According to the methodological approach discussed in the paper, the landslide hazard analysis should start from a phenomenological interpretation of the slope behaviour, including the definition of the slope factors, getting then to a quantitative prediction of the slope evolution with time. This quantitative evaluation should result from limit equilibrium analyses and numerical modelling, both of them performed considering the outcomes of the phenomenological reconstruction. Therefore, the understanding of the slope factors and of the landslide mechanism at the slope scale should drive the landslide hazard assessment, through analyses performed for different levels of diagnosis (phenomenological, analytical and numerical). Some landslides, representative for chain slopes in the Italian peninsula, are discussed in the paper in order to show the maturity of the geohydromechanical diagnosis of landslide hazard and, hence, to properly design the mitigation actions. A methodology for intermediate to regional landslide hazard assessment, based on geomechanical interpretations, is finally proposed.

Interpretation of landslide mechanisms based on numerical modelling: two case-histories

Numerical modelling represents a powerful technique to develop a quantitative assessment of the stress–strain mechanisms leading to either first-time slope failures or evolution of slopes already failed in the past. In this perspective, a valid interpretation of the landslide behaviour and an adequate strategy of risk mitigation can be achieved from a numerical validation of both the causative factors and the evolution mechanism that have been previously assumed according to detailed phenomenological or simple analytical approaches. This paper presents two case histories of slow landslides in clay slopes, both located in Puglia (Southern Italy), for which detailed phenomenological studies have been firstly carried out to infer assumptions on the slope failure mechanisms that have been later on verified by means of numerical analyses accounting for soil mechanical behaviour and slope hydraulic processes. The first case study concerns the first-time failure of a stiff clay slope in Lucera, which has been induced by the slow dissipation of negative excess pore water pressures generated by previous quarry excavation at the slope toe. The second case history is represented by the analysis of the stress–strain evolution of the ancient Volturino landslide, which is observed to reactivate mainly in wet seasons.

Diagnosis of Slow Landslides Affecting Tectonised Clayey Slopes (Southern Apennines)

The assessment of the slope failure mechanisms, along with the identification of the factors promoting the development of the landslide processes, represents the keystone for an effective design of landslide mitigation. The paper outlines some mitigation strategies for some slow-moving landslides, involving heterogeneous and tectonized soils, located in the outer sector of Southern Apennines. These mitigation designs result from a comprehensive analysis of the failure slope scenarios as resulted from field surveys and investigations, slope monitoring and laboratory testing.

Landslide hazard assessment and judgment of reliability: a geomechanical approach

Landslide hazard maps are often defined as reliable a posteriori, in accordance with the real landslides occurring from the time of the map production. However, to be useful for planning, a reliability judgment concerning the hazard mapping should be a priori, based on data uncertainty characterization, and must be driven by the knowledge of the slope instability mechanisms. The landslide hazard assessment, when based on the deterministic diagnosis of the processes, may really lead to really providing clues about how and why the slope could fail (landslide susceptibility) and, possibly, when (landslide hazard). Such deterministic assessment can be pursued only through the interpretation and the geo-hydro-mechanical modelling of the slope equilibrium. In practice, though, the landslide hazard assessment is still seldom dealt with slope modelling, in particular when it addresses intermediate to regional zoning. The paper firstly offers an overview of the key steps of a methodology called the multiscalar method for landslide mitigation, MMLM, which that is a methodological approach for the intermediate to regional landslide hazard assessment using the hydro-mechanical diagnoses of landsliding. The validation of the MMLM to the geologically complex outer sectors of the Southern Apennines (Daunia-Lucanian mountains; Italy) is also delineated, together with a practical approach to incorporate a reliability judgment in the landslide susceptibility/hazard mapping.

Localisation Processes and Size Effects for Fissured Clay Specimens

The paper presents the results of Digital Image Correlation (DIC) method applied to plane strain tests carried out on specimens of fissured clays from the south of Italy. Information about physical properties and Fissuring IDentity of the clays are reported together with an outline of the global behaviourial framework of the fissured clay Represententative Element Volume (REV). DIC has been used to explain some discrepancies found in the global shearing behaviour of some specimens which did not fit the framework. DIC revealed the sources of such discrepancies, which made these specimens much smaller than the REV.