Sabatino Cuomo

Modeling of Rainfall-Induced Shallow Landslides of the Flow-Type

The paper deals with the modeling of failure and postfailure stage of shallow landslides of the flow-type that often affect natural shallow deposits of colluvial, weathered, and pyroclastic origin. The failure stage is frequently associated to rainfall that directly infiltrates the slope surface and to spring from the underlying bedrock. The postfailure stage is characterized by the sudden acceleration of the failed mass. The geomechanical modeling of both stages, based on site conditions and soil mechanical behavior, represents a fundamental issue to properly assess the failure conditions and recognize the potential for long travel distances of the failed soil masses. To this aim, in this paper, the current literature on the failure and postfailure stages of the shallow landslides of the flow-type is first reviewed. Then, an approach for their geomechanical modeling is proposed and three different modeling alternatives are presented. These models are then used to analyze, at different scales, a relevant case study of Southern Italy Sarno-Quindici event, May 4-5, 1998. Numerical analyses outline that both site conditions and hydraulic boundary conditions are among the key factors to evaluate the reliability of landslides of the flow-type. The potentialities and limitations of the available models are also evidenced as well as the perspectives related to the use of more advanced numerical models.

Application of a SPH depth-integrated model to landslide run-out analysis

Hazard and risk assessment of landslides with potentially long run-out is becoming more and more important. Numerical tools exploiting different constitutive models, initial data and numerical solution techniques are important for making the expert’s assessment more objective, even though they cannot substitute for the expert’s understanding of the site-specific conditions and the involved processes. This paper presents a depth-integrated model accounting for pore water pressure dissipation and applications both to real events and problems for which analytical solutions exist. The main ingredients are: (i) The mathematical model, which includes pore pressure dissipation as an additional equation. This makes possible to model flowslide problems with a high mobility at the beginning, the landslide mass coming to rest once pore water pressures dissipate. (ii) The rheological models describing basal friction: Bingham, frictional, Voellmy and cohesive-frictional viscous models. (iii) We have implemented simple erosion laws, providing a comparison between the approaches of Egashira, Hungr and Blanc. (iv) We propose a Lagrangian SPH model to discretize the equations, including pore water pressure information associated to the moving SPH nodes.

Seasonal effects of rainfall on the shallow pyroclastic deposits of the Campania region (southern Italy)

The shallow deposits of unsaturated pyroclastic soils covering the slopes in the Campania region (southern Italy) are systematically affected by various rainfall-induced slope instabilities. The type and triggering of these instabilities depend on several factors, among which in situ soil suction—as an initial condition—and rainfall—as a boundary condition—play a fundamental role. Based on the available database—which includes a comprehensive catalogue of historical data, in situ soil suction measurements and soil laboratory tests along with the results of geomechanical analyses—this paper discusses the relationships among in situ soil suction and rainfall conditions and induced slope instability types. The goal is to reach a better understanding of past events and gain further insight into the analysis and forecasting of future events. In particular, the paper outlines how the season strongly affects the spatial distribution and the type of slope instability likely to develop. For example, erosion phenomena essentially occur at the end of the dry season and originate hyperconcentrated flows while first-time shallow slides prevail in the rainy season and later propagate as debris flows or as debris avalanches.

Inception of debris avalanches: remarks on geomechanical modelling

Debris avalanches are complex phenomena due to the variety of mechanisms that control the failure stage and the avalanche formation. Regarding these issues, in the literature, either field evidence or qualitative interpretations can be found while few experimental laboratory tests and rare examples of geomechanical modelling are available for technical and/or scientific purposes. As a contribution to the topic, the paper firstly highlights as the problem can be analysed referring to a unique mathematical framework from which different modelling approaches can be derived based on limit equilibrium method (LEM), finite element method (FEM), or smooth particle hydrodynamics (SPH). Potentialities and limitations of these approaches are then tested for a large study area where huge debris avalanches affected shallow deposits of pyroclastic soils (Sarno-Quindici, Southern Italy). The numerical results show that LEM as well as uncoupled and coupled stress–strain FEM analyses are able to individuate the major triggering mechanisms. On the other hand, coupled SPH analyses outline the relevance of erosion phenomena, which can modify the kinematic features of debris avalanches in their source areas, i.e. velocity, propagation patterns and later spreading of the unstable mass. As a whole, the obtained results encourage the application of the introduced approaches to further analyse real cases in order to enhance the current capability to forecast the inception of these dangerous phenomena.

Inverse Analysis for Rheology Calibration in SPH Analysis of Landslide Run-Out

Landslide run-out modeling is an important issue in engineering-based procedures for landslide hazard assessment. Nowadays, several numerical techniques are available among which Smooth Particle Hydrodynamic (SPH) is a promising tool which ensures reasonable computational times to achieve an accurate description of the main kinematic quantities such as heights and velocities of the mobilized volume(s). The reliability of run-out modeling is mostly based on the comparison of numerical results and field evidences, from which the selection of the most appropriate rheological model and the calibration of the rheological parameters are obtained. Rheology calibration is usually based on trial/error procedures which, in turn, rely on expert-judgment and/or previous acquired experiences for the same type of phenomenon. In the paper, an inverse analysis procedure is tested to calibrate a simple frictional rheological model within a SPH analysis of a case study for which a detailed data-set of in situ evidences is available.

Spatially distributed analysis of soil erosion in a mountain catchment

A spatial-distributed soil erosion analysis model was applied to a small-sized mountain catchment of Southern Italy, where shallow deposits of loose, cohesionless unsaturated air-fall volcanic (pyroclastic) soils exist. The physically-based LISEM model was used to analyze a past event, taking into account the potential role of both the soil suction and water content, and the spatial variability of soil thickness. The water discharge and the solid concentration at the outlet of the catchment were computed, as well as the spatial distribution of the eroded soil thickness was discussed for the uppermost areas of the catchment. The results of the paper show that the soil suction and the soil conductivity are key factors for the spatial-temporal evolution of both ground infiltration and runoff in the catchment. concentration (from low to high and vice-versa), which, in turn, are related to the water discharge at the outlet of a mountain catchment (Cascini et al., 2014). As far as the amount of the mobilized sediments, a wide range of erosion models exist, empirical or physically-based which differ each other depending on their overall complexity, number of processes considered and data required in realistic applications to boundary value problems. One common output of any erosion model is the spatial distribution of the eroded areas (Della Sala et al., 2013, 2014). The erosion patterns can be the result of long-term rainfalls and/or caused by one (or few) specific rainstorms. However, an accurate quantitative assessment of the soils eroded by a specific rainstorm can be only obtained through a physically-based model. This quantitative output information is necessary, for instance, when the design of the erosion control works is dealt with, aimed to mitigate the risk posed to life and property. It is worth noting that the physically-based soil erosion models are based on the solution of the fundamental equations of mass and momentum conservation for the water flow and mass sediment conservation (Merritt et al., 2003), and they require detailed input data, which often are uncertain for real case studies; in these cases, simplified assumptions are necessary to perform the analyses. The paper deals with a relevant case study of unsaturated soils, with field evidence available for: principal slope instabilities recorded at the uppermost areas of the catchment; the peak total discharge and solid volume at the outlet of the catchment where huge damage was caused. The principal aim was to investigate the spatial-temporal features of the erosion process throughout the

Penetration tests in shallow layered unsaturated pyroclastic soil deposits of Southern Italy

The paper deals with a recent extensive in-situ and laboratory investigation carried out in a site characterized by thin layered unsaturated air-fall volcanic (pyroclastic) soil deposits, which are very steep and prone to slope failures turning into catastrophic flows (Cervinara, Southern Italy). The field campaign was based on iron-rod drillings, penetration tests and hand-excavated shafts, beside to the collection of undisturbed soil specimens used for laboratory tests. The real sequence of the soil layers was identified in more than two hundreds verticals. In addition, while a series of available literature formulas are detected as unreliable for these soils, the paper propose new reliable empirical correlations between the soil friction angle (of three lithotypes) and both the number of blows of the penetration test and the vertical stress.

LARAM School 2018: the doctoral school on “LAndslide Risk Assessment and Mitigation”

The international school for PhD students and young doctors on “LAndslide Risk Assessment and Mitigation” (LARAM) is presented and, specifically, information is provided about the next edition of the doctoral school that will held in Italy, at the University of Salerno, on September 3–14, 2018. The LARAM School is managed by the Geotechnical Engineering Group (GEG) of the University of Salerno, which recently became an Associate member of the International Consortium on Landslides (ICL). The 2018 edition of the LARAM School is organised as an ICL/IPL activity.

Propagation Modeling and Inverse Analysis of a Landslide in Hong Kong

Landslide propagation modeling is an important task in susceptibility and hazard analyses. Model reliability is typically assessed comparing numerical results to field observations. In this paper, the Smooth Particle Hydrodynamic (SPH) method and an inverse analysis procedure are used to calibrate the soil rheological parameters for a well-document landslide case history in Honk Kong. Two rheological laws are herein considered to simulate the behavior of the debris during propagation: single mixed-phase material depending on one frictional parameter; two-phase frictional material described by three additional input parameters regulating the consolidation process within the solid skeleton saturated with water. The results obtained by the performed analysis clearly indicate that the two-phase rheology outperforms the single phase one. Yet, in the latter case, some of the input parameters are correlated, thus they cannot be calibrated independently in the optimization procedure.

Insights from LS-RAPID Modeling of Montaguto Earthflow (Italy)

Open image in new window The paper deals with the numerical modeling of the Montaguto earthflow (Italy), as typical case of multi-stage flow-type landslide, formerly analyzed subdividing the whole process in subsequent stages. The paper proposed a unique simplified model including: (i) slope stability analysis to simulate the landslide initiation process due to pore pressure increase and (ii) landslide dynamic analysis for propagation, volume enlargement by entrainment and energy dissipation due to frictional, non-frictional and velocity dependent terms. The numerical results are capable to provide a substantial framework for interpreting the main kinematic and morphological features of the landslide.