Nicola Sciarra

SPH modeling of fast muddy debris flow: numerical and experimental comparison of certain commonly utilized approaches

SPH (Smoothed Particle Hydrodynamics) is a particle, purely mesh-free Lagrangian method, proposed by different authors, well suited to the computing of highly transitory free surface flows of complex fluids in complex geometries. Different approaches have been proposed in order to better simulate the mutual interaction between particles and their interactions with boundaries. Therefore, the main target of this article is to discuss and explore the numerical performance of certain commonly utilized SPH approaches, based essentially on mass and momentum balances, in the simulation of a 2D fast mudflow in fast motion, composed of fluid and solid material, assumed to be just one equivalent phase (fluid-solid). The “Herschel-Bulkley”, non Newtonian constitutive equations, describing a viscoplastic material suitable to reproduce the rheological behaviour of mudflows, has been selected. Hence, a laboratory experimental test, already proposed in literature and, after properly scaling, representative of a real fast flow phenomenon, was considered for comparison with numerical outcomes carried out by a research code that has already been tested and discussed in previous papers. A simple but effective statistical approach was developed and applied in order to identify and utilize a numerical index suitable for the quantitative measurement of the degree of matching between numerical results and measurement data affected by experimental errors. More than thirty numerical experiments were performed, of which the most significant eleven simulations are discussed. Satisfactory results were achieved. As outcomes, it was verified that, in particular for the selected experimental test, Rusanov flux addition within the continuity equation with the proper choice of both the viscosity term of momentum and the SPH boundary conditions, is suited to enhancing the performance of this type of numerical simulation of a fast flow.

2D modelling of large-scale platform margin collapses along an ancient carbonate platform edge (Maiella Mt., Central Apennines, Italy): geological model and conceptual framework

Abstract Results of numerical simulations of large-scale platform margin collapses along the edge of the Cretaceous platform of the Maiella (Central Apennines) are presented, adding a new contribution to the understanding of the role and quantification of the various factors that control triggering of these phenomena and the production of breccias and megabreccias. For this purpose, a sophisticated numerical code, widely used in recent contexts to simulate overall mass movements and deep gravity-driven deformation, is applied for the first time to an ancient system on a scale of several kilometres. The modelling carried out is a simplified attempt to understand a very complex phenomenon produced over a very long time-span. It tests whether the perturbing causes in the model, acting together or separately, are able to activate such large-scale collapse, and helps to understand the effects of perturbing causes and their variations. In particular, modelling was carried out considering both static (variations in sea level) and dynamic (seismic events without and with fault formation) conditions and combinations of them. Variations in sea level alone do not produce all the effects observed but may certainly be a predisposing element. Seismic shock simulations show that fracturing and shear stresses are concentrated on the platform margin, representing the most sensitive and vulnerable area. Earthquake swarms associated with an active fault are the most likely means of triggering large-scale platform margin collapses, such as those occurring during the Early Cretaceous in the Maiella.

Geomorphological features of the Montebello sul Sangro large landslide (Abruzzo, Central Italy)

ABSTRACT This work presents the first results of an integrated geomorphological analysis of a large earthflow in Montebello sul Sangro (Abruzzo, Central Italy). The study is based on a multitemporal geomorphological investigation supported by the morphometric analysis of the drainage network and numerical landslide modelling. The multitemporal geomorphological investigation, based on the interpretation of aerial photos, LiDAR data and field geomorphological mapping, outlined the recent geomorphological history and multiple activation phases of the landslides. A 2D Finite Difference Method (FLAC, Fast Lagrangian Analysis of Continua) analysis of the main landslide scarp, affecting the village of Montebello sul Sangro (Italy), was performed. Finally, in order to outline the morphometric features of the landslide area, local slope autocorrelation was used as a morphometric index. The analysis was aimed at studying the evolution of the active current landslide and specifically the possible retreat of the main scarp.

Conceptual and Numerical Models Applied on the River Pellice (North Western Italy)

Modelsareasimplifyingabstractionofreality.Furthermore,theyprovideoneofthecruciallinks between the analysis of processes and the study of the world around us, the two traditional activities of geomorphology. Starting from these considerations, the present research illustrates the reconstruction of spatial variation in channel morphology in the long, medium and shortterm period using the traditional geomorphologic methods of investigation. This reconstruction allows a preliminary comparison with the conceptual model of the Italian rivers but it leaves several doubts on river evolution in the short-term period. As a consequence, the numerical modelhasbeenintroduced inordertoestimateandevaluateasetofevolutionaryscenariosalong the river and to give an answer to its future evolution. In our research activity, we have applied the Conceptual Evolution Model (CEM) proposed by Surian and Rinaldi and its following updating for the Italian rivers and a cellular automaton (CA) model (CAESAR) at the case-study of the River Pellice, left tributary of the River Po in North Western Italy.

First results of morphometric analysis, multitemporal geomorphological investigation and numerical modeling of the Montebello sul Sangro landslide (Abruzzo, Central Italy)

In this work the first results of an integrated geomorphological analysis of a large earth flow in Montebello sul Sangro (Abruzzo, Central Italy) are presented. The study is based on a new morphometric analysis of the drainage network, a multitemporal geomorphological investigation and a numerical landslide modeling. In order to reconstruct the topography of the Montebello area before the landslide and, accordingly, to explore the possible triggering causes of the instability phenomena, autocorrelation of local slope was introduced as a morphometric index. Multitemporal geomorphological investigation is based on the interpretation of aerial photos, LiDAR data and field geomorphological mapping. The analysis allowed for the outline of the recent multiple activation phases of the landslides. Finally, a 2D Finite Difference Method (FLAC) analysis of a slope, particularly representative because close to the village of Montebello sul Sangro (Italy), was performed.

Application of CAESAR for catchment and river evolution

In recent years the application of reduced complexity models (RCM) is proving to be an excellent alternative resource for evaluating the hydrological response of catchments within a period of time up to decades. In addition, the past two decades have seen significant improvements in the study of river morphology, in particular with regard to the analysis of the processes governing the fluvial evolution resulting from the erosion and transport of sediments. Hence, this paper is aimed at the discussion of the employment of the research code CAESAR, based on cellular automaton (CA) approach, in order to evaluate the water and the sediment outputs from an alpine catchment. Then, the output of the model is applied to a river reach in order to forecast the river evolution in the near future.

DSGSDs Induced by Post-Glacial Decompression in Central Apennine (Italy)

During the last 30 years of studies in the field of mass movements located in the calcareous-marly and marly-sandy Apennines (Umbria-Marches and Latium-Abruzzi regions), over to a large number of landslides with different dimensions, even a lot of deep-seated gravitational slope deformations (DSGSDs) have been recognized and analysed. These phenomena are also located in that sector of central Italy affected by a cold climate during the past and actually temperate (central Apennine chain).

Slope Stability Modelling of a Sandstone Cliff South of Livorno (Tuscany, Italy)

This paper will examine a sandstone cliff south of the town of Livorno Italy, between the Rio Maroccone mouth to the north and the Leone cove to the south, in its most dangerous area, between the sea and the main road Aurelia. The aim of this paper is to divide the area into homogenous hazard classes and assess the possible kinematic evolution. The paper refers to an evaluation of parameters that may trigger rock falls on the cliff, which could constitute dangers for tourists. The identification of critical areas has been achieved through the elaboration of landslide susceptibility maps. The geotechnical study was carried out on the Macigno Fm at the site. Field surveys and indirect tests for classifying rock masses and estimating the uniaxial compression strength (UCS) were performed. Some numerical analyses were executed to study the static and dynamic behavior of the slope. The results confirm the vulnerability of the areas, demonstrating the dynamic instability of the analyzed sections and a precarious equilibrium is also in static conditions. These analyses, compared with the site surveys, show poor data and in some cases alarming results; some portions of the cliff are under limit equilibrium conditions or close to it, especially in some of the areas appreciated by tourists and bather. Through the numerical modeling the critical situation of these slopes becomes even more evident, confirmed by some rock falls of small blocks occurred during the geomechanical survey period. To make the situation even worse, the whole area is constantly subject to exogenous agents such as strong winds and the wave action, which determine a rapid deterioration of the mechanical characteristics of strength in the Macigno Sandstone.

Water and Sediment Output Evaluation Using Cellular Automata on Alpine Catchment: Soana, Italy - Test Case

In the alpine contest, the estimation of the rainfall (inflow) and the discharge (outflow) data are very important in order to, at least, analyse historical time series at catchment scale; determine the hydrological maximum and minimum estimate flood and drought frequency. Hydrological researches become a precious source of information for various human activities, in particular for land use management and planning. Many rainfall- runoff models have been proposed to reflect steady, gradually-varied flow condition inside a catchment. In these last years, the application of Reduced Complexity Models (RCM) has been representing an excellent alternative resource for evaluating the hydrological response of catchments, within a period of time up to decades. Hence, this paper is aimed at the discussion of the application of the research code CAESAR, based on cellular automaton (CA) approach, in order to evaluate the water and the sediment outputs from an alpine catchment (Soana, Italy), selected as test case. The comparison between the predicted numerical results, developed through parametric analysis, and the available measured data are discussed. Finally, the analysis of a numerical estimate of the sediment budget over ten years is presented. The necessity of a fast, but reliable numerical support when the measured data are not so easily accessible, as in Alpine catchments, is highlighted.

Hazard assessment of a complex landslide: the case of Vestea (Abruzzo, Italy)

This short note aims to reconstruct the geomorphological hazard scenarios connected to the complex landslide that insists on the territory of Vestea (Civitella Casanova Municipality, in the province of Pescara, Italy). The landslide, active for several decades, probably since the XIX century, is located along a wide valley and starting from its head. It manifests frequently local reactivations with varying movement typology; while total reactivations, taking place in concomitance of particular climate and hydrogeological factors, are more rare.