Spreading of Kaolin and Sand Mixtures on a Horizontal Plane: Physical Experiments and SPH Numerical Modelling

open4noThe investigation of the collapse of a well-known soil volume is a simple experiment that permits to make several interesting considerations. This paper, at first, presents a brief overview of some physical experiments led to understand how the composition of a three-phase mixture influences the mass collapse. In particular, the run-out and the maximum height of the deposit are considered as two fundamental quantities for characterizing the behaviour of the mass in each test. In a second step, the experimental results obtained are used as case studies for the calibration of a mesh-less numerical model. Several simulations are carried out using the SPH-Geoflow code implementing a Bingham law to reproduce each bi-phases test. A comparison between the numerical results and the physical data permits to choose the most reliable value of the constitutive parameters for each tested case. The errors between the physical and the numerical run-out and maximum heights become the fundamental quantity to define the quality of the best simulation. Indeed, some final considerations about the relationship existing among the constitutive parameters and the kaolin content of the mixtures are reported.openBrezzi, Lorenzo; Cola, Simonetta; Gabrieli, Fabio; Gidoni, GiacomoBrezzi, Lorenzo; Cola, Simonetta; Gabrieli, Fabio; Gidoni, Giacom

A new data assimilation procedure to develop a debris flow run-out model

Abstract Parameter calibration is one of the most problematic phases of numerical modeling since the choice of parameters affects the model\u2019s reliability as far as the physical problems being studied are concerned. In some cases, laboratory tests or physical models evaluating model parameters cannot be completed and other strategies must be adopted; numerical models reproducing debris flow propagation are one of these. Since scale problems affect the reproduction of real debris flows in the laboratory or specific tests used to determine rheological parameters, calibration is usually carried out by comparing in a subjective way only a few parameters, such as the heights of soil deposits calculated for some sections of the debris flows or the distance traveled by the debris flows using the values detected in situ after an event has occurred. Since no automatic or objective procedure has as yet been produced, this paper presents a numerical procedure based on the application of a statistical algorithm, which makes it possible to define, without ambiguities, the best parameter set. The procedure has been applied to a study case for which digital elevation models of both before and after an important event exist, implicating that a good database for applying the method was available. Its application has uncovered insights to better understand debris flows and related phenomena

Calibration strategies of a depth-integrated numerical model for the propagation of flow-like landslides

Nowadays, the numerical models are important allies for the study of physical and natural phenomena. They become progressively more complicated because various differential equations are included to consider the different processes involved in a singular phenomenon. The number of parameters used to adapt the numerical results to the real measurements increase consequently. Among the huge quantity of natural phenomena studied, the landslides are definitely important and, among them, the flow-slides are a type, which actually have an increasing occurrence frequency because of the climate change. When the velocity of the flowing material is high, this type of natural hazard becomes even more worrying. The risk and the damage, which may result, are significant, especially when the landslide is located in close proximity to residential areas. The catastrophic effects range from the destruction of buildings and infrastructures, to the most tragic loss of human lives. Three processes of a flow-slide could be individuated: the trigger mechanism, the propagation and the final deposit. Topic of this thesis is the study of the last two phases that occur after the mass collapse has already happened. The propagation and the deposit phases will be here analyzed using a model which integrates the Saint Venant‘s equations developed for the flow of an equivalent homogeneous material according to the shallow water hypothesis. The model is applied before to the simulation of several laboratory experiments and, then, for reproducing a debris flow really occurred in 2010 in Italy. The calibration phase is the basic operation for using a numerical model. The parameters considered have to be smartly defined to reproduce the phenomenon with a satisfactory likelihood. When the parameters have a physical meaning, it is necessary to check if they allow the model to produce reliable results, even when the model necessarily introduces strong approximations. Sometimes, anyway, the parameters to include in the calculation have just a mathematical significance. In this case, it is even more important to calibrate the model paying attention to all the complexities of the phenomenon, because if the calibration strategy does not take into account the various aspects of the case study, the parameters obtained by the back-analysis may be senseless. This thesis wants to show the complexity that may characterize the calibration procedure. Once the numerical model has been adopted and its possibilities and limitations have been evaluated, the analysis of different cases will help to evidence the difficulties that the back-analysis can present. To this aim, in this work, three main case studies are presented: the spreading of a column of cohesive material on a horizontal plane, numerous flume tests performed using three-phases mixtures and, finally, a real debris flow occurred in 2010 along the Rotolon stream, in North-Western sector of Veneto region (Italy). It is important to underline that all the laboratory tests are performed on purpose to apply the back-analysis, paying therefore particular attention to the data acquisition conditions. For all the case studies, many calibration procedures are applied in order to individuate the most suitable to reduce the uncertainty in the determination of the fitting parameters

Calibration strategies of a depth-integrated numerical model for the propagation of flow-like landslides

Nowadays, the numerical models are important allies for the study of physical and natural phenomena. They become progressively more complicated because various differential equations are included to consider the different processes involved in a singular phenomenon. The number of parameters used to adapt the numerical results to the real measurements increase consequently. Among the huge quantity of natural phenomena studied, the landslides are definitely important and, among them, the flow-slides are a type, which actually have an increasing occurrence frequency because of the climate change. When the velocity of the flowing material is high, this type of natural hazard becomes even more worrying. The risk and the damage, which may result, are significant, especially when the landslide is located in close proximity to residential areas. The catastrophic effects range from the destruction of buildings and infrastructures, to the most tragic loss of human lives. Three processes of a flow-slide could be individuated: the trigger mechanism, the propagation and the final deposit. Topic of this thesis is the study of the last two phases that occur after the mass collapse has already happened. The propagation and the deposit phases will be here analyzed using a model which integrates the Saint Venant‘s equations developed for the flow of an equivalent homogeneous material according to the shallow water hypothesis. The model is applied before to the simulation of several laboratory experiments and, then, for reproducing a debris flow really occurred in 2010 in Italy. The calibration phase is the basic operation for using a numerical model. The parameters considered have to be smartly defined to reproduce the phenomenon with a satisfactory likelihood. When the parameters have a physical meaning, it is necessary to check if they allow the model to produce reliable results, even when the model necessarily introduces strong approximations. Sometimes, anyway, the parameters to include in the calculation have just a mathematical significance. In this case, it is even more important to calibrate the model paying attention to all the complexities of the phenomenon, because if the calibration strategy does not take into account the various aspects of the case study, the parameters obtained by the back-analysis may be senseless. This thesis wants to show the complexity that may characterize the calibration procedure. Once the numerical model has been adopted and its possibilities and limitations have been evaluated, the analysis of different cases will help to evidence the difficulties that the back-analysis can present. To this aim, in this work, three main case studies are presented: the spreading of a column of cohesive material on a horizontal plane, numerous flume tests performed using three-phases mixtures and, finally, a real debris flow occurred in 2010 along the Rotolon stream, in North-Western sector of Veneto region (Italy). It is important to underline that all the laboratory tests are performed on purpose to apply the back-analysis, paying therefore particular attention to the data acquisition conditions. For all the case studies, many calibration procedures are applied in order to individuate the most suitable to reduce the uncertainty in the determination of the fitting parameters.Oggigiorno, i modelli numerici ricoprono un ruolo di fondamentale importanza per lo studio di fenomeni fisici e naturali. Essi diventano via via sempre più complessi grazie all’aumento del numero di equazioni differenziali implementate in ciascun modello al fine di tener conto dei differenti aspetti che caratterizzano il fenomeno oggetto studio. Conseguentemente cresce anche il numero dei parametri da valutare per adattare i risultati ottenuti dal modello numerico alle misure reali. Tra tutti i fenomeni naturali che si possono considerare, i frane sono indiscutibilmente molto importanti. Tra i diversi tipi di frane, le colate sono una tipologia che si presenta sempre con maggior frequenza a causa dei cambiamenti climatici in atto e con effetti molto dannosi. Quando, poi, la velocità raggiunta in questi fenomeni diventa elevata, aumenta il loro potere distruttivo. I rischi e i danni che ne possono nascere non sono trascurabili, in modo particolare quando le colate avviene in prossimità di aree residenziali. Gli effetti catastrofici che ne possono scaturire spaziano dalla distruzione di edifici e infrastrutture, fino ad arrivare alla ancor più tragica perdita di vite umane. Quando si studia un movimento di colata, tre processi devono essere presi in considerazione: il meccanismo di innesco, la fase di propagazione ed infine il deposito. Questa tesi riguarda principalmente lo studio degli ultimi due processi che si verificano, cioè, quando il materiale ha già iniziato il suo movimento. Le fasi di propagazione e di arresto sono qui analizzate utilizzando un modello numerico sviluppato integrando le equazioni di Saint Venant per il flusso di un materiale monofase omogeneo in acque basse. Il modello è stato applicato sia per la simulazione di esperimenti di laboratorio sia per riprodurre un debris flow avvenuto nel nord Italia nel 2010. Quando si utilizza un modello numerico, la fase di calibrazione rappresenta un’operazione essenziale affinché si possano ottenere buoni risultati. I parametri utilizzati dal codice devono essere attentamente definiti in modo che il modello possa riprodurre il fenomeno fisico con elevata accuratezza. Quando i parametri hanno un significato fisico, risulta necessario controllare se il loro utilizzo, considerando le approssimazioni che il modello inevitabilmente comporta, permette di produrre risultati affidabili. A volte, tuttavia, i parametri che devono essere inseriti nel modello prescindono dalla natura fisica del caso in esame, ed hanno solamente un significato in termini matematici. Quando questo avviene, risulta ancor più importante calibrare il modello, cercando di cogliere l’intera complessità del fenomeno. Se la strategia di calibrazione non tiene conto dei vari aspetti che caratterizzano il caso di studio, infatti, i parametri ottenuti tramite back-analysis potrebbe non aver alcun senso. Questa tesi si pone l’obiettivo di sottolineare la complessità che può contraddistinguere il processo di calibrazione. Dopo aver deciso quale modello numerico utilizzare ed averne comprese possibilità e limitazioni, lo studio di casi di studio differenti permette di evidenziare le criticità e le problematiche che la back-analysis può presentare. A tale scopo, in questo lavoro vengono considerati principalmente tre casi di studio. Il primo riguarda il collasso di una colonna di materiale coesivo su di un piano orizzontale. Successivamente la procedura è applicata ad un gruppo di prove in canaletta condotte con diverse miscele di argilla e sabbia. Infine, viene analizzata la colata detritica avvenuta nel 2010 lungo il torrente Rotolon, situato in nella parte nord-occidentale del Veneto. È importante sottolineare che tutti i test di laboratorio sono stati eseguiti appositamente per la successiva applicazione della back-analysis, prestando quindi particolare attenzione alle modalità di acquisizione dei dati. Per tutti e tre i casi, è stata ricercata ed applicata una strategia di calibrazione per ridurre l’incertezza nell’identificazione dei parametri ottimali

Wadenow: A Matlab Toolbox for Early Forecasting of the Velocity Trend of a Rainfall-Triggered Landslide by Means of Continuous Wavelet Transform and Deep Learning

A procedure aimed at forecasting the velocity trend of a landslide for a period of some hours to one or two days is proposed here together with its MATLAB implementation. The method is based on continuous wavelet transform (CWT) and convolutional neural network (CNN) applied to rainfall and velocity time series provided by a real-time monitoring system. It is aimed at recognizing the conditions that induce a strong increase, or even a significant decrease, in the average velocity of the unstable slope. For each evaluation time, the rainfall and velocity scalograms related to the previous days (e.g., two weeks) are computed by means of CWT. A CNN recognizes the velocity trend defined in the training stage corresponds to these scalograms. In this way, forecasts about the start, persistence, and end of a critical event can be provided to the decision makers. An application of the toolbox to a landslide (Perarolo di Cadore landslide, Eastern Alps, Italy) is also briefly described to show how the parameters can be chosen in a real case and the corresponding performance

Calibration of rheological properties of materials involved in flow-like landslides

One of the effects of climate change is an expansion of the areas affected by flow-like landslides and an increase in human loss and economic damage caused by these natural hazards. The risk assessment connected to flow-like landslides utilizes several study approaches, such as the mapping of lands affected in the past, the understanding of triggering and propagation mechanisms through the monitoring of some watershed basins periodically subject to flow-like landslides, and the prediction of flow-like landslide propagation by means of advanced mathematical models. Research has made much progress in the development of advanced mathematical models able to account for various rheological models, 3D morphology of the slope, and engagement of other materials from the boundary, etc. Calibration of the parameters is, however, one of the most problematic phases of numerical modelling; the validation of propagation models is usually carried out on the basis of laboratory flume tests executed in very simple conditions or on the basis of data achieved from field observation, which are very often of low quality. After a brief state-of-art review concerning the most recent developments in flow-like landslide modelling, the present paper examines the techniques adopted for calibrating the models. Particularly, it considers the difficulties linked to the upscaling of rheological properties moving from the physical tests performed in viscometer or artificial flume, and attaining the estimation of average properties of the heterogeneous materials involved in real flow-like landslides

AUTOMATIC RECOGNITION AND VOLUME CALCULATION OF LANDSLIDE COLLAPSE AREA BASED ON IMAGE SEQUENCE

Digital photogrammetry technology based on fixed multi-view cameras has attracted widespread attention in the field of geotechnical engineering due to its low-cost and contactless mode. For the purpose of studying the surface collapse of a landslide monitored with these low-cost cameras, we have developed a photogrammetric algorithm that can quickly detect the collapses, determine the collapse area and calculate the collapse volume. With the field data and small-scale experiments, we have verified the accuracy of the program. The method of quickly and automatically obtaining collapse information proposed in this paper will improve the efficiency of landslide monitoring system based on photos and it is of great significance for further research and the realization of a collapse prediction tool

Post-Collapse Evolution of a Rapid Landslide from Sequential Analysis with FE and SPH-Based Models

none6Propagation models can study the runout and deposit of potential flow-like landslides only if a reliable estimate of the shape and size of the volumes involved in the phenomenon is available. This aspect becomes critical when a collapse has not yet occurred and the estimation of the unstable volume is not uniquely predictable. This work proposes a strategy to overcome this problem, using two established analysis methods in sequence; first, a Strength Reduction Method (SRM)-based 3D FEM allows the estimate of the instable volume; then, this data becomes an input for a Smoothed Particle Hydrodynamics (SPH)-based model. This strategy is applied to predict the possible evolution of Sant’Andrea landslide (North-Eastern Italian Alps). Such a complex landslide, which affects anhydrite–gypsum rocks and is strongly subject to rainfall triggering, can be considered as a prototype for the use of this procedure. In this case, the FEM–SRM model is adopted, which calibrates using mapping, monitoring, geophysical and geotechnical data to estimate the volume involved in the potential detachment. This volume is subsequently used as the input of the SPH model. In this second phase, a sensitivity analysis is also performed to complete the evaluation of the most reliable final soil deposits. The performed analyses allow a satisfactory prediction of the post-collapse landslide evolution, delivering a reliable estimate of the volumes involved in the collapse and a reliable forecast of the landslide runout.noneBrezzi, L.; Carraro, E.; Pasa, D.; Teza, G.; Cola, S.; Galgaro, A.Brezzi, L.; Carraro, E.; Pasa, D.; Teza, G.; Cola, S.; Galgaro, A

Distributed optical fiber systems for monitoring the serviceability strain response of an Italian concrete arch dam and its foundation

Concrete arch dams are large constructions aiming at producing hydroelectricity, providing water for irrigation and controlling flooding. Although the maximization of the water level of the basin allows to optimize the management of the dam, an accurate monitoring of such large structures must be carried out carefully to evaluate the deformations in operational conditions. Traditionally, the monitoring of the dam body as function of the environmental temperature and reservoir water level is performed through visual inspections, periodic manual surveys or topographical measurements. Nevertheless, this monitoring is complex and time consuming due to the considerable spatial extension of dams. Recently, both traditional survey and innovative techniques for field monitoring have greatly improved, making these checks faster and more complete. In this context, the use of Distributed Optical Fiber Sensors (DFOS) as detector of strain and temperature can be considered a very attractive option, allowing the measurements of spatially dense and distributed data along large distances and with high resolution. The paper deals with the monitoring of a concrete double arch dam, namely Ponte Cola dam, located in Valvestino (BS) in North Italy. Between December 2020 and February 2021, two different types of DFOS both in the foundation and along the crown of the dam were installed. The DFOS are one for strain and one for temperature measurement. Several measurement campaigns were carried out. These measurements have been compared with the ones obtained from traditional monitoring techniques, to estimate the reliability and potentiality of such an innovative system in monitoring the very low strains developed in this type of structures