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 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.

The activity of deep landslides in slopes formed of clayey turbidites has been observed to be connected to the climatic regime in the Mediterranean, based on field data and phenomenological interpretations. With the aim of investigating this connection, the effects of the soil–vegetation–atmosphere interaction on the piezometric regime were investigated by means of hydraulic finite-element analyses of the transient seepage across a prototype clayey slope. The ground surface condition was defined accounting for rainfall and evapotranspiration flux, estimated through the United Nations' Food and Agriculture Organization Penman–Monteith approach. The predicted excursions of the piezometric head within the slope over time were found to agree with field observations. The predicted piezometric profiles were investigated to evaluate the infiltration processes during the year and show how these bring about seasonal piezometric excursions. The results of the hydraulic analyses were then input into limit equilibrium analyses to assess the impact of the slope–vegetation–atmosphere interaction on the stability of landslide bodies of different depths. The results show how such impact depends on the stratigraphy of the slope. Furthermore, the variability of the climatic precursor of landsliding with landslide depth was characterised to guide the design of early warning systems for mitigation purposes.

The paper reports the results of a slope-atmosphere interaction analysis performed with reference to geo-hydro-mechanical conditions typically observed on the Southern Apennines (Italy). The aim of the analysis is to gain some understanding in the characterisation of climatic variables employed to identify instability thresholds in clay slopes. A seepage analysis was undertaken first, showing that Mediterranean climates can produce significant pore-pressure changes also at depths not usually considered to be affected by atmospheric conditions. Based on the results of the seepage analysis, limit equilibrium analyses were carried out for a 5 m and a 20 m deep landslide, confirming that also deep movements in clay slopes can be related to slope-atmosphere interaction. The characterisation of climatic variables aimed at identifying instability thresholds is finally discussed based on the analyses reported in the paper. The results show that net rainfall cumulated over 2 and 6 months represent suitable climatic variables for the 5 m and the 20 m deep landslide, respectively. These findings suggest that the stability of a clay slope, when referred to shallow movements, is likely to depend on the rainfall infiltrating over a few weeks at least. When deep movements are considered, the stability seems to depend more on the rainfall gradually infiltrating during the most rainy seasons.

This paper discusses the relation of the coefficient of saturated permeability in a given direction, k_i, with the void ratio, e, for fissured and unfissured clays, wherein k_i characterises the hydraulics of the equivalent uniform porous model. The k_i–e data for the fissured clays are compared with what is observed for unfissured clays, either natural or reconstituted. For each clay, the k_i–e data result from laboratory investigation and are related to the fissuring identity of the clay, classified through a fissuring characterisation chart. Through this procedure, the study provides an initial rational insight of the variability of the k_i–e law with both the micro- and the meso-scale clay features. Fissuring is shown to cause meso-scale non-uniformities of the flow patterns, which may cause a variation between the k_i for steady-state seepage and that controlling transient seepage. In general, fissuring increases the clay permeability with respect to the same clay if unfissured and also with respect to the same clay when reconstituted. Also, the study sheds light on the difference between the k_i–e law holding during compression and that during swelling for both unfissured and fissured clays, showing that such difference is more important for fissured clays.