Pendant une éruption volcanique sur des sommets englacés, des coulées de débris syn-eruptifs,dénommées lahars, peuvent être générées par la fonte partiale de glaciers. Ce phénomène estbien connu sur le volcan Cotopaxi, Equateur. La présente étude concerne trois vallées et un cônede déjection sur le flanc sud-ouest de ce volcan. Une première analyse a été conduite par relevésde formes géomorphologiques dans ces vallées qui témoignent des processus d’érosion et desédimentation lors du passage de lahars dans le passé, notamment ceux du dernier événementéruptif datant de 1877 AD. Bien que les types des formes géomorphologiques déterminées sontles mêmes, leur distribution spatiale varie d’une vallée à l’autre en fonction d’une interaction deparamètres morphologiques locaux. Les conditions environnementales individuelles déterminentégalement le volume de l’écoulement, paramètre crucial dans la délimitation de zones de risques delahars dans les plaines adjacentes. Pour cela, une deuxième étude a été menée à grande échelle surle cône de déjection à l’exutoire de la vallée la plus au Sud des trois. Une analyse intégrale de la morphologiede surface et des affleurements naturels a été complétée par des données stratigraphiquesde subsurface obtenues via un sondage avec un Géoradar. Reconstituer l’architecture sédimentairede ce cône permet de visualiser la distribution spatiale de formes érosives et de dépôts. L’étude àrévélé que différentes parties du cône sont actives à des moments distincts et les épaisseurs dedépôts de lahars sont variables en fonction du type d’écoulement et de son volume. Ceci permetde relier les dynamiques géomorphologiques des plaines alluviales aux zones d’initiation de laharssur les flancs du volcan. Enfin, cette étude a débouché sur la mise en place d’une nouvelle fonctiondans le logiciel de modélisation de lahars LAHARZ prenant en compte l’incorporation progressive desédiment dans un contexte érosif dans les vallées, ce qui permet une meilleure délimitation de zonesde risque de lahars sur le cône. / During a volcanic eruption at ice capped volcanoes, syn-eruptive volcanic debris flows, lahars, canbe triggered through the partial melting of the glaciers. This phenomenon is well known to have happenedat Cotopaxi volcano, Ecuador, where the present study has been realized. The latter concernsthree drainages on the southwestern flank of the volcano and one alluvial fan. A first analysis hasbeen conducted assessing geomorphologic features in the drainages testifying from erosional anddepositional processes during past lahars, in particular of those generated during the last eruptiveevent dating back to 1877 AD. Although the types of determined geomorphologic features are thesame, their spatial distribution varies among the three valleys as a function of an interplay of localmorphologic parameters. The individual environmental conditions determine also the flow volumeof such lahars, a critical parameter when to delineating hazard zones in the adjacent lowlands. Thesecond analysis has therefore be performed at large scale on the alluvial fan forming at the mouthof the southernmost of the three drainages. An integral study of the surface morphology and naturalexposures was enriched with subsurface stratigraphic information obtained through a ground penetratingradar survey. The sediment architecture of the fan provides valuable insights on the distributionof erosional features and deposits. Different fan parts appear to be active at different times andlahar deposit thicknesses are highly variable as a function of flow type and volume. This allows torelate floodplain dynamics to the initiation zone of lahars on the upper flanks of the volcano. At last,this research led to integrate a new bulking function acknowledging for erosional processes in thevalleys into the lahar-modeling software LAHARZ allowing to better delineate lahar hazard zones onthe fan.

Dans le présent travail, nous étudions l'impact sur un obstacle rigide d'un écoulement transitoire à surface libre de fluide viscoplastique. Cette étude est conduite numériquement à l'aide de la méthode SPH (Smoothed Particle Hydrodynamics), en y intégrant le modèle rhéologique de Herschel-Bulkley. Le code employé est adapté à nos besoins et validé sur des cas test classiques. Les caractéristiques locales de l'écoulement à proximité de l'obstacle sont analysées et deux régimes d'impact sont mis en évidence en fonction de la pente d'écoulement. L'étude des pressions exercées sur l'obstacle, conduite spatialement et temporellement en fonction de ces régimes d'impact, nous permet de mettre en évidence les rôles respectifs des composantes gravitationnelle et cinétique de la pression. Nos résultats sont comparés systématiquement à des résultats expérimentaux issus de travaux précédents et sont cohérents avec ces derniers. Une étude comparative de nos écoulements de fluide viscoplastique avec des écoulements de matériau granulaires de propriétés similaires nous conduit à mettre en évidence des caractéristiques communes entre les deux matériaux. / In this work, we study the impact of a transient free-surface flow of viscoplastic fluid on a rigid obstacle. This study is conducted numerically using the SPH (Smoothed Particle Hydrodynamics) method, and the Herschel-Bulkley rheological model. The SPH code is adapted to our needs and validated on classic benchmarks. The local characteristics of the flow near the obstacle are analysed and two impact regimes are highlighted depending on the slope angle. By studying of the pressure exerted on the obstacle, both spatially and temporally, with regards to these impact regimes, we evidence the respective roles of the gravitational and kinetic components of the pressure. Our results are systematically compared with experimental data from a previous work and are shown to be consistent. A comparative study conducted on both our viscoplastic flows and flows of granular material of similar properties highlights common characteristics of the two materials.

Dans le présent travail, nous étudions l'impact sur un obstacle rigide d'un écoulement transitoire à surface libre de fluide viscoplastique. Cette étude est conduite numériquement à l'aide de la méthode SPH (Smoothed Particle Hydrodynamics), en y intégrant le modèle rhéologique de Herschel-Bulkley. Le code employé est adapté à nos besoins et validé sur des cas test classiques. Les caractéristiques locales de l'écoulement à proximité de l'obstacle sont analysées et deux régimes d'impact sont mis en évidence en fonction de la pente d'écoulement. L'étude des pressions exercées sur l'obstacle, conduite spatialement et temporellement en fonction de ces régimes d'impact, nous permet de mettre en évidence les rôles respectifs des composantes gravitationnelle et cinétique de la pression. Nos résultats sont comparés systématiquement à des résultats expérimentaux issus de travaux précédents et sont cohérents avec ces derniers. Une étude comparative de nos écoulements de fluide viscoplastique avec des écoulements de matériau granulaires de propriétés similaires nous conduit à mettre en évidence des caractéristiques communes entre les deux matériaux. / In this work, we study the impact of a transient free-surface flow of viscoplastic fluid on a rigid obstacle. This study is conducted numerically using the SPH (Smoothed Particle Hydrodynamics) method, and the Herschel-Bulkley rheological model. The SPH code is adapted to our needs and validated on classic benchmarks. The local characteristics of the flow near the obstacle are analysed and two impact regimes are highlighted depending on the slope angle. By studying of the pressure exerted on the obstacle, both spatially and temporally, with regards to these impact regimes, we evidence the respective roles of the gravitational and kinetic components of the pressure. Our results are systematically compared with experimental data from a previous work and are shown to be consistent. A comparative study conducted on both our viscoplastic flows and flows of granular material of similar properties highlights common characteristics of the two materials.

Este trabajo fue realizado en la quebrada Huaycoloro el cual forma parte de la cuenca que lleva el mismo nombre ubicada en el distrito de Lurigancho-Chosica en la provincia de Lima, donde se busca explicar los criterios de modelación de flujo de detritos aplicando dos modelos matemáticos de análisis para este tipo de flujos. El primero de libre acceso KANAKO-2D y el segundo de acceso de paga FLO-2D, ambos modelos requieren datos de entrada en común como la topografía digital del terreno, valores de rugosidad del canal, hidrogramas para diferentes periodos de retorno, propiedades reológicas del fluido a dos fases (agua-sedimento) entre otros. Para esta investigación se realizó un Modelo de Elevación Digital (DEM por sus siglas en inglés) con resolución espacial de 5mx5m, donde al hidrograma liquido se le añade el porcentaje de concentración de sedimentos para la representación del flujo de escombros en los modelos correspondientes, los parámetros reológicos (viscosidad, porcentaje de concentración, esfuerzo de cedencia) son tomados de manera referencial comparando resultados de estudios hechos en la quebrada con muestras validadas recopiladas de la literatura. Para finalmente con el procesamiento de estos datos en ambos programas, obtener resultados como profundidad de flujo, velocidad, concentración de sedimentos, fuerza de impacto, etc. De los cuales, este artículo se centró en la comparación de la profundidad del flujo de escombros de los respectivos modelamientos con un evento real, donde para el modelo Kanako-2D, Flo-2D y la medida en campo se presenta una profundidad promedio de 2.20, 2.50 y 2.60 metros respectivamente, por lo que se concluye que el programa Flo-2D es más preciso en su modelamiento para esta situación en especial. / This work was carried out in the Huaycoloro stream which is part of the basin that bears the same name located in the district of Lurigancho-Chosica in the province of Lima, where it seeks to explain the criteria of debris flow modeling applying two mathematical models analysis for this type of flows. The first one with free access KANAKO-2D and the second one with paid access FLO-2D, both models require common input data such as digital terrain topography, channel roughness values, hydrographs for different return periods, rheological properties of the two-phase fluid (water-sediment) among others. For this research, a Digital Elevation Model (DEM) was carried out with spatial resolution of 5mx5m, where the percentage of sediment concentration is added to the liquid hydrograph to represent the debris flow in the corresponding models, the Rheological parameters (viscosity, concentration percentage, yield stress) are taken as a reference, comparing results of studies carried out in the stream with validated samples collected from the literature. Finally, with the processing of these data in both programs, obtain results such as flow depth, velocity, sediment concentration, impact force, etc. Of which, this article focused on the comparison of the depth of the debris flow of the respective modeling with a real event, where for the Kanako-2D, Flo-2D and the field measurement an average depth of 2.20 is presented , 2.50 and 2.60 meters respectively, so it is concluded that the Flo-2D program is more accurate in its modeling for this particular situation. / Trabajo de investigación

La presente tesis aplica un análisis de tendencias asociados a la variación de la energía de impacto y localización que tienen las barreras flexibles ante eventos de flujos de detritos. Esto para establecer y considerar la variabilidad anteriormente mencionada como un parámetro de diseño para barreras flexibles y, por consiguiente, desarrollar una propuesta de ingeniería eficaz que permita maximizar el comportamiento de las barreras flexibles y sea aplicable a diferentes proyectos que consideren como propuesta estructuras de contención dinámica para frenar el impacto de los flujos de detritos. Todo esto tomando en cuenta los parámetros geotécnicos e hidro morfológicos de la zona, con principal importancia en la pendiente y la precipitación como desencadenante de eventos de flujos de detritos. El estudio se desarrolló en la quebrada Primero de Mayo ubicado en el distrito de Lurigancho, departamento de Lima, Perú. Tomando en cuenta que es una quebrada sin presencia de estructuras de contención previas y con un crecimiento poblacional no controlado que aumenta el riesgo de pérdidas económicas y sociales en la zona. Las simulaciones del comportamiento de las barreras flexibles ante diferentes situaciones de energía y localización se desarrollaron en el software Rocfall para establecer el número de barreras necesario para contener el flujo de detritos de la zona y plantear cuatro diferentes iteraciones para el estudio. / The proposal of a probabilistic factor is presented to determine the percentage of failure that can occur in shallow foundations, in our case footings. In this article we will present a comparison between the safety factor (F.S), defined by the standard E050 Soils and Foundations, and the probability of failure. This method will be executed through the simulation of input data, such as specific weight, cohesion, angle of friction and load stress. For this simulation process, the Monte Carlo method will be applied. Once the soil resistance values ​​have been obtained, considering its normal distribution and the stress, the probabilities of failure will begin to be analyzed using the strength and stress density curves. Finally, we will analyze the relationship that will occur between the F.S and the probability of failure to observe the behavior when increasing the parameters for resistance. / Trabajo de investigación

El presente trabajo consiste en el modelamiento hidrológico e hidráulico de la quebrada Huaycoloro ubicado en el distrito de Lurigancho – Chosica con fin de proponer soluciones de mitigación estructural y no estructural que integren los modelos. Comenzando por un análisis de eventos de flujo de escombros en el Perú con marco teórico que aborda conceptos básicos relacionados al estudio de hidrología e hidráulica. Para el modelo hidrológico, se realizó la caracterización de la cuenca de la quebrada obteniendo sus parámetros principales, así también se realizó el análisis de precipitaciones y así realizar un modelamiento hidrológico mediante HEC-HMS en colaboración con ArcGIS y determinar caudales máximos con periodo de retorno de 100, 200 y 500 años. El modelo hidráulico fue trabajado con el software FLO-2D PRO y el software libre japonés KANAKO -2D, cuyos parámetros de entrada son hidrogramas calculados por el modelo hidrológico, la topografía digital del terreno, los parámetros físicos y reológicos del flujo, entre otros. Para luego obtener velocidades y profundidades máximas para cada uno de los periodos de retorno mencionados anteriormente cuyos resultados serán comparados entre sí en determinados puntos de control y así precisar cuál de ambos softwares es el mejor, para posteriormente modelar los escenarios incluidas las estructuras y poder determinar su óptimo pre-dimensionamieto y analizar su nivel de mitigación frente al impacto de los flujos de escombros. Finalmente, se realizó la comparación de las modelaciones con estructuras y se propuso de manera conceptual y básica medidas no estructurales, realizando su respectivo análisis, viabilidad y eficiencia para mitigar este tipo de eventos. / The present work consists of the hydrological and hydraulic modeling of the Huaycoloro stream located in the district of Lurigancho - Chosica in order to propose structural and non-structural mitigation solutions that integrate the models. Starting with an analysis of debris flow events in Peru with a theoretical framework that addresses basic concepts related to the study of hydrology and hydraulics. For the hydrological model, the characterization of the basin of the creek was carried out, obtaining its main parameters, as well as the analysis of precipitation and thus perform a hydrological modeling using HEC-HMS in collaboration with ArcGIS and determine maximum flows with return period of 100, 200 and 500 years. The hydraulic model was worked with the FLO-2D PRO software and the Japanese free software KANAKO -2D, whose input parameters are hydrographs calculated by the hydrological model, the digital topography of the terrain, the physical and rheological parameters of the flow, among others. To then obtain maximum velocities and depths for each of the aforementioned return periods, the results of which will be compared with each other at certain control points and thus determine which of the two softwares is the best to subsequently model the scenarios including the structures and be able to determine their optimum pre-dimensioning and analyze their level of mitigation against the impact of debris flows. Finally, a comparison of the modeling with structures was carried out and non-structural measures were proposed in a conceptual and basic manner, performing their respective analysis, feasibility and efficiency to mitigate this type of events. / Tesis

Several regions of the Western United States utilize statistical binary classification models to predict and manage debris flow initiation probability after wildfires. As the occurrence of wildfires and large intensity rainfall events increase, so has the frequency in which development occurs in the steep and mountainous terrain where these events arise. This resulting intersection brings with it an increasing need to derive improved results from existing models, or develop new models, to reduce the economic and human impacts that debris flows may bring. Any development or change to these models could also theoretically increase the ease of collection, processing, and implementation into new areas. Generally, existing models rely on inputs as a function of rainfall intensity, fire effects, terrain type, and surface characteristics. However, no variable in these models directly accounts for the shear stiffness of the soil. This property when considered with the respect to the state of the loading of the sediment informs the likelihood of particle dislocation, contractive or dilative volume changes, and downslope movement that triggers debris flows. This study proposes incorporating shear wave velocity (in the form of slope-based thirty-meter shear wave velocity, Vs30) to account for this shear stiffness. As commonly used in seismic soil liquefaction analysis, the shear stiffness is measured via shear wave velocity which is the speed of the vertically propagating horizontal shear wave through sediment. This spatially mapped variable allows for broad coverage in the watersheds of interest. A logistic regression is used to then compare the new variable against what is currently used in predictive post-fire debris flow triggering models. Resulting models indicated improvement in some measures of statistical utility through receiver operating characteristic curves (ROC) and threat score analysis, a method of ranking models based on true/false positive and negative results. However, the integration of Vs30 offers similar utility to current models in additional metrics, suggesting that this input can benefit from further refinement. Further suggestions are additionally offered to further improve the use of Vs30 through in-situ measurements of surface shear wave propagation and integration into Vs30 datasets through a possible transfer function. Additional discussion into input variables and their impact on created models is also included.

In environmental impact assessment (EIA), accident risk should be considered as one impact. However, few studies have compared assessed risk levels with documented accidents. There is thus a need for assessing accuracy of risk assessment methodologies. The aim of this study was to develop and examine a risk assessment guideline based on environmental assessment. The guideline examination was carried out along the railway and the road between Kiruna and Narvik, Northern Scandinavia. The examined hazards were avalanches, debris flows, rock falls, slush flows, torrents, moose and reindeer. Documented accidents were quantified into an accident level. For each hazard type, six sections/sites were assessed. The propensities of these hazards were analysed through environmental assessments, especially by utilising geomorphology. Then, the accident densities along the sections/sites were compared with assessed accident phase indices describing risk and hazard in both spatial and temporal dimensions. The average uncertainty factors for both the risk and the hazard indices were about 5. This implies a fairly good precision. Risk and hazard indices were also rated and compared to the accident density rates. Thereafter, railway and road information was split up as different proposal alternatives in an EIA context. The total risk for each proposal was compared with the total accident density. The risk assessment guideline proved to be cost-efficient, rapid and relatively reliable in comparing accident risk.

In environmental impact assessment (EIA), accident risk should be considered as one impact. However, few studies have compared assessed risk levels with documented accidents. There is thus a need for assessing accuracy of risk assessment methodologies. The aim of this study was to develop and examine a risk assessment guideline based on environmental assessment. The guideline examination was carried out along the railway and the road between Kiruna and Narvik, Northern Scandinavia. The examined hazards were avalanches, debris flows, rock falls, slush flows, torrents, moose and reindeer. Documented accidents were quantified into an accident level. For each hazard type, six sections/sites were assessed. The propensities of these hazards were analysed through environmental assessments, especially by utilising geomorphology. Then, the accident densities along the sections/sites were compared with assessed accident phase indices describing risk and hazard in both spatial and temporal dimensions. The average uncertainty factors for both the risk and the hazard indices were about 5. This implies a fairly good precision. Risk and hazard indices were also rated and compared to the accident density rates. Thereafter, railway and road information was split up as different proposal alternatives in an EIA context. The total risk for each proposal was compared with the total accident density. The risk assessment guideline proved to be cost-efficient, rapid and relatively reliable in comparing accident risk.

L’objectif de cette thèse est de développer un modèle numérique 3D afin d’étudier le phénomène de laves torrentielles ; écoulements visqueux fortement chargés en matière solide, surgissant en montagne lors d’orages violents. Aujourd’hui, la prévision des zones de vulnérabilité s’appuie sur des outils de calcul 0D, 1D ou 2D. Or ces outils ne peuvent représenter pleinement le comportement à surface libre des écoulements du fait de nombreuses approximations et hypothèses. Ainsi cette thèse met en œuvre un code numérique 3D pour étudier ces écoulements. Ce travail aboutit à la construction d’un modèle 3D à partir de données réelles de terrain. Plusieurs scénarios ont été étudiés et comparés à des résultats issus d’un modèle 2D. Les résultats mettent en évidence les apports non négligeables de la modélisation 3D : zones d’étalement et de dépôt, phénomènes d’encombrement, modélisation fine des écoulements dans les zones chenalisées. Préalablement, le modèle 3D a été validé en comparant les résultats numériques à des données expérimentales issues de la littérature, pour des typologies d’écoulement représentatives de celles observées sur des sites grandeur nature. / The objective of this thesis is to develop a 3D numerical model to assess debris flow. These viscous flows, heavily loaded with solid matter, form when heavy rain occurs in mountains. Today, forecasts of potentially impacted areas are based on 0D, 1D and 2D numerical tools. However, these tools cannot fully represent the free surface behaviour of debris flows due to the approximations and assumptions on which they are based. Thus, this work utilises a 3D numerical code to study this phenomenon. A specific model is built with real field data. Several flow scenarios are studied and compared with a 2D numerical model. The results highlight the significant benefits of a 3D approach by providing information on the fine representation of flow dynamics over the catchment area. The model also predicts the impact of debris flow (overflowing on a road bridge) and the zones of deposition and spreading. It highlights possible congestion phenomena and reproduces flows in the channels by fully accounting for parietal friction, capabilities not provided by 2D models. Prior to this application, the 3D model was evaluated with five sets of experimental data to validate its ability to represent viscoplastic flows. Different types of flows are studied and are representative of those observed on real sites when debris flow occur.