Acceleration Characteristics of a Rock Slide Using the Particle Image Velocimetry Technique

The Particle Image Velocimetry (PIV) technique with high precision and spatial resolution is a suitable sensor for flow field experiments. In this paper, the PIV technology was used to monitor the development of a displacement field, velocity field and acceleration field of a rock slide. It was found that the peak acceleration of the sliding surface appeared earlier than the peak acceleration of the sliding body. The characteristics of the rock slide including the short failure time, high velocities, and large accelerations indicate that the sliding forces and energy release rate of the slope are high. The deformation field showed that the sliding body was sliding outwards along the sliding surface while the sliding bed moved in an opposite direction. Moving upwards at the top of the sliding bed can be one of the warning signs for rock slide failure

Landslide motion assessment including thermal interaction : an MPM approach

Risk associated with landslides of natural or man-made origin depends on the prediction of the post-failure behaviour of the mobilized mass. Numerical models capable of integrating the landslide geometry and its evolution, the coupled hydro mechanical interaction and the soil properties in the context of dynamic forces and large displacements are currently under development. This thesis is a contribution to this effort. In this sense, the material point method (MPM) is especially suited for analyzing landslides with large displacements. This numerical procedure must be accompanied by tests under controlled conditions in order to accurately check and calibrate the numerical response. In this thesis the capabilities of the MPM code developed are evaluated through the modelling of scaled laboratory slope tests with large displacements. In order to achieve an adequate comparison of the experimental and numerical results, the experiments are analysed by means of the interpretation of sequential digital images of the movement of the granular medium during the test (PIV technique). A novel procedure is developed to obtain the field of deformations over time and the tracking of particle path in a manner suitable for comparison with numerical results calculated in MPM. The main objective of the thesis was the development of a comprehensive calculation tool capable of simulating the behaviour of the slides from the initial triggering to the post-failure phase including thermal effects that determine the evolution of the movement. A formulation for non-isothermal problems coupled with hydraulic and mechanical behaviour in MPM was developed and implemented. The formulation includes the dissipation of frictional work as heat, which takes place, mainly, in shear bands. The described phenomena are strongly dependent on the thickness of the shear band and this result in a strong dependence of the numerical results in MPM with the discretization mesh. A novel procedure to solve this problem is presented in this thesis. Finally, very rapid Vajont landslide (Italy 1963) is modelled. A plain strain 2D model is presented without an “a priori” definition of the sliding surface. In fact, in a generalization of previous and recent work, the mobilized materials are not restricted to rigid solids interconnected along a predefined contact surface and the heat generation is not it is limited to a single predefined surface. Thus, thermal interaction processes are developed throughout the model as a function of the location and intensity of deformations.El riesgo asociado con deslizamientos de origen natural o artificial depende de la predicción del comportamiento posterior a la rotura de la masa movilizada. Actualmente se están desarrollando modelos numéricos capaces de integrar la geometría del deslizamiento y su evolución, la interacción hidromecánica acoplada y las propiedades del suelo en el contexto de fuerzas dinámicas y grandes desplazamientos. Esta tesis es una contribución a este esfuerzo. En este sentido, el método del punto material (MPM) es especialmente adecuado para analizar deslizamientos con grandes desplazamientos. Este procedimiento numérico debe ir acompañado de ensayos bajo condiciones controladas para poder comprobar y calibrar la respuesta numérica. En esta tesis se evalúan las capacidades del código MPM desarrollado, mediante la modelación de ensayos de laboratorio a escala con grandes desplazamientos. Para lograr una adecuada comparación de los resultados experimentales y numéricos, se analizan los experimentos mediante la interpretación de imágenes digitales secuenciales del movimiento del medio granular durante el ensayo (técnica PIV). Con este fin, se desarrolla un procedimiento novedoso para la obtención del campo de deformaciones en el tiempo y el seguimiento de la trayectoria de las partículas de forma idónea para la comparación con resultados numéricos calculados en MPM. El principal objetivo de la tesis fue el desarrollo de una herramienta potente de cálculo capaz de simular el comportamiento de los deslizamientos desde la rotura inicial hasta la fase de post-rotura incluyendo efectos térmicos que determinan la evolución del movimiento. Para esto, se desarrolla e implementa una formulación para problemas no isotérmicos acoplados con el comportamiento hidráulico y mecánico en MPM. Esta formulación incluye la disipación del trabajo friccional en forma de calor, lo cual ocurre principalmente en las bandas donde se localiza la deformación de corte. Este fenómeno descrito es fuertemente dependiente con el espesor de la banda de corte y esto se traduce en una fuerte dependencia de los resultados numéricos en MPM con la malla de discretización empleada. En esta tesis se presenta un novedoso procedimiento para solventar este problema. Por último se presenta la modelación del movimiento ocurrido en el deslizamiento rápido de Vajont (Italia 1963). Se introduce un modelo 2D en deformación plana sin una definición "a priori" de la superficie de deslizamiento. De hecho, generalizando los trabajos hechos anteriormente, los materiales movilizados no se restringen a solidos rígidos interconectados a lo largo de una superficie de contacto predefinida y la generación de calor no se limita a una única superficie predefinida. Así, los procesos de interacción térmica se desarrollan en todo el modelo en función de la localización e intensidad de las deformaciones.Postprint (published version

Landslide generated impulse waves

Landslide generated impulse waves were investigated in a two-dimensional physical laboratory model based on the generalized Froude similarity. Digital particle image velocimetry (PIV) was applied to the landslide impact and wave generation. Areas of interest up to 0.8m by 0.8m were investigated. The challenges posed to the measurement system in an extremely unsteady three-phase flow consisting of granular matter, air, and water were considered. The complex flow phenomena in the first stage of impulse wave initiation are: high-speed granular slide impact, slide deformation and penetration into the fluid, flow separation, hydrodynamic impact crater formation, and wave generation. During this first stage the three phases are separated along sharp interfaces changing significantly within time and space. Digital masking techniques are applied to distinguish between phases thereafter allowing phase separated image processing. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into the kinematics of the wave generation process. Differential estimates such as vorticity, divergence, elongational, and shear strain were extracted from the velocity vector fields. The fundamental assumption of irrotational flow in the Laplace equation was confirmed experimentally for these non-linear waves. Applicability of PIV at large scale as well as to flows with large velocity gradients is highlighte

Experimental Study of Sub-aerial, Submerged and Transitional Granular Slides in Two and Three Dimensions

«RÉSUMÉ: Les glissements de terrain sont reconnus comme des dangers naturels avec des dommages majeurs qui peuvent causer un danger pour la vie humaine et/ou des pertes matérielles en raison de leur comportement destructeur. Ils se produisent généralement près des régions montagneuses (classées comme des glissements de terrain non submergés ou sous-aériens) ou près des zones côtières telles que les océans, les lacs, les berges des rivières, les baies (considérées comme des glissements de terrain sous-marins) qui génèrent des vagues destructrices de grande amplitude, semblables à des tsunamis.» et «----------ABSTRACT: Landslides are recognized as natural hazards with massive casualties and loss of properties due to their damaging behavior. They usually happen near the mountainous regions (classified as unsubmerged or sub-aerial landslides) or near coastal areas such as oceans, lakes, riverbanks, bays (considered as submarine landslides) that generates destructive tsunami-like waves with high amplitudes. Deformable landslides usually can be regarded as the downward movement of granular material on an inclined and/or flat plane due to their nature. In this regard, in the present study, we experimentally investigate the gravity-driven slide of granular materials for various slope angles, material types, bed roughness, and flow regimes in 2D and 3D experimental setups.

Physical modeling of tsunamis generated by three-dimensional deformable granular landslides

Tsunamis are gravity water waves that are generated by impulsive disturbances such as submarine earthquakes, landslides, volcanic eruptions, underwater explosions or asteroid impacts. Submarine earthquakes are the primary tsunami source, but landslides may generate tsunamis exceeding tectonic tsunamis locally, in both wave and runup heights. The field data on landslide tsunami events are limited, in particular regarding submarine landslide dynamics and wave generation. Tsunamis generated by three-dimensional deformable granular landslides are physically modeled in the NEES (Network of Earthquake Engineering Simulation) 3D tsunami wave basin (TWB) at Oregon State University in Corvallis, Oregon. A novel pneumatic landslide tsunami generator is deployed to simulate natural landslide motion on a hill slope. The instrumentation consists of various underwater, above water and particle image velocimetry (PIV) cameras, numerous wave and runup gauges and a multi-transducer acoustic array (MTA). The subaerial landslide shape and kinematics on the hill slope and the surface elevation of the offshore propagating tsunami wave and runup on the hill slope are measured. The evolution of the landslide front velocity, maximum landslide thickness and width are obtained along the hill slope. The landslide surface velocity distribution is obtained from the PIV analysis of the subaerial landslide motion. The shape and the size of the submarine landslide deposit are measured with the MTA. Predictive equations are obtained for the tsunami wave amplitude, wave period and wavelength in terms of the non-dimensional landslide parameters. The generated 3D tsunami waves propagate away from the landslide source as radial wave fronts. The amplitudes of the leading tsunami waves decay away from the landslide source in radial and angular direction. The wave celerity of the leading tsunami wave may be approximated by the solitary wave speed while the trailing waves are slower due to the dispersion effects. The energy conversion rate between the landslide and the generated wave is estimated. The observed waves are weakly non-linear in nature and span from shallow water to deep water depth regime. The unique experimental data serves the validation and advancement of numerical models of tsunamis generated by landslides. The obtained predictive equations facilitate initial rapid tsunami hazard assessment and mitigation.Ph.D.Fritz, Herman

Grain Reynolds number scale effects in dry granular slides

©2020. The Authors. Scale effects are differences in physical behavior that manifest between a large event and a geometrically scaled laboratory model and may cause misleading predictions. This study focuses on scale effects in granular slides, important in the environment and to industry. A versatile 6 m long laboratory setup has been built following Froude similarity to investigate dry granular slides at scales varied by a factor of 4, with grain Reynolds numbers Rein the range of 102 to 103. To provide further comparison, discrete element method simulations have also been conducted. Significant scale effects were identified; the nondimensional surface velocity increased by up to 35%, while the deposit runout distance increased by up to 26% from the smallest to the largest model. These scale effects are strongly correlated with Re, suggesting that interactions between grains and air are primarily responsible for the observed scale effects. This is supported by the discrete element method data, which did not show these scale effects in the absence of air. Furthermore, the particle drag force accounted for a significant part of the observed scale effects. Cauchy number scale effects caused by unscaled particle stiffness resulting in varying dust formation with scale are found to be of secondary importance. Comparisons of the laboratory data to that of other studies and of natural events show that data normalization with Re is an effective method of quantitatively comparing laboratory results to natural events. This upscaling technique can improve hazard assessment in nature and is potentially useful for modeling industrial flows

Landslide motion assessment including thermal interaction : an MPM approach

Risk associated with landslides of natural or man-made origin depends on the prediction of the post-failure behaviour of the mobilized mass. Numerical models capable of integrating the landslide geometry and its evolution, the coupled hydro mechanical interaction and the soil properties in the context of dynamic forces and large displacements are currently under development. This thesis is a contribution to this effort. In this sense, the material point method (MPM) is especially suited for analyzing landslides with large displacements. This numerical procedure must be accompanied by tests under controlled conditions in order to accurately check and calibrate the numerical response. In this thesis the capabilities of the MPM code developed are evaluated through the modelling of scaled laboratory slope tests with large displacements. In order to achieve an adequate comparison of the experimental and numerical results, the experiments are analysed by means of the interpretation of sequential digital images of the movement of the granular medium during the test (PIV technique). A novel procedure is developed to obtain the field of deformations over time and the tracking of particle path in a manner suitable for comparison with numerical results calculated in MPM. The main objective of the thesis was the development of a comprehensive calculation tool capable of simulating the behaviour of the slides from the initial triggering to the post-failure phase including thermal effects that determine the evolution of the movement. A formulation for non-isothermal problems coupled with hydraulic and mechanical behaviour in MPM was developed and implemented. The formulation includes the dissipation of frictional work as heat, which takes place, mainly, in shear bands. The described phenomena are strongly dependent on the thickness of the shear band and this result in a strong dependence of the numerical results in MPM with the discretization mesh. A novel procedure to solve this problem is presented in this thesis. Finally, very rapid Vajont landslide (Italy 1963) is modelled. A plain strain 2D model is presented without an “a priori” definition of the sliding surface. In fact, in a generalization of previous and recent work, the mobilized materials are not restricted to rigid solids interconnected along a predefined contact surface and the heat generation is not it is limited to a single predefined surface. Thus, thermal interaction processes are developed throughout the model as a function of the location and intensity of deformations.El riesgo asociado con deslizamientos de origen natural o artificial depende de la predicción del comportamiento posterior a la rotura de la masa movilizada. Actualmente se están desarrollando modelos numéricos capaces de integrar la geometría del deslizamiento y su evolución, la interacción hidromecánica acoplada y las propiedades del suelo en el contexto de fuerzas dinámicas y grandes desplazamientos. Esta tesis es una contribución a este esfuerzo. En este sentido, el método del punto material (MPM) es especialmente adecuado para analizar deslizamientos con grandes desplazamientos. Este procedimiento numérico debe ir acompañado de ensayos bajo condiciones controladas para poder comprobar y calibrar la respuesta numérica. En esta tesis se evalúan las capacidades del código MPM desarrollado, mediante la modelación de ensayos de laboratorio a escala con grandes desplazamientos. Para lograr una adecuada comparación de los resultados experimentales y numéricos, se analizan los experimentos mediante la interpretación de imágenes digitales secuenciales del movimiento del medio granular durante el ensayo (técnica PIV). Con este fin, se desarrolla un procedimiento novedoso para la obtención del campo de deformaciones en el tiempo y el seguimiento de la trayectoria de las partículas de forma idónea para la comparación con resultados numéricos calculados en MPM. El principal objetivo de la tesis fue el desarrollo de una herramienta potente de cálculo capaz de simular el comportamiento de los deslizamientos desde la rotura inicial hasta la fase de post-rotura incluyendo efectos térmicos que determinan la evolución del movimiento. Para esto, se desarrolla e implementa una formulación para problemas no isotérmicos acoplados con el comportamiento hidráulico y mecánico en MPM. Esta formulación incluye la disipación del trabajo friccional en forma de calor, lo cual ocurre principalmente en las bandas donde se localiza la deformación de corte. Este fenómeno descrito es fuertemente dependiente con el espesor de la banda de corte y esto se traduce en una fuerte dependencia de los resultados numéricos en MPM con la malla de discretización empleada. En esta tesis se presenta un novedoso procedimiento para solventar este problema. Por último se presenta la modelación del movimiento ocurrido en el deslizamiento rápido de Vajont (Italia 1963). Se introduce un modelo 2D en deformación plana sin una definición "a priori" de la superficie de deslizamiento. De hecho, generalizando los trabajos hechos anteriormente, los materiales movilizados no se restringen a solidos rígidos interconectados a lo largo de una superficie de contacto predefinida y la generación de calor no se limita a una única superficie predefinida. Así, los procesos de interacción térmica se desarrollan en todo el modelo en función de la localización e intensidad de las deformaciones

Tsunamis generated by fast granular landslides: 3D experiments and empirical predictors

Landslides falling into water bodies can generate impulsive waves, which are a type of tsunamis. The propagating wave may be highly destructive for hydraulic structures, civil infrastructure and people living along the shorelines. A facility to study this phenomenon was set up in the laboratory of the Technical University of Catalonia. The set-up consists of a new device releasing granular material at high velocity into a wave basin. A system employing laser sheets, high-speed and high-definition cameras was designed to accurately measure the high velocity and geometry of the sliding mass as well as the produced water displacement in time and space. The analysis of experimental data helped to develop empirical relationships linking the landslide parameters with the produced wave amplitude, propagation features and energy, which are useful tools for the hazard assessment. The empirical relationships were successfully tested in the case of the 2007 event that occurred in Chehalis Lake (Canada).Peer ReviewedPostprint (author's final draft

Particle Image Velocimetry (PIV) for Positron Emission Particle Tracking (PEPT) and Turbulence Modeling Validation

A Particle Image Velocimetry (PIV) experiment is designed and data collected with intention to validate Positron Emission Particle Tracking (PEPT) methods. The PIV data are collected in a narrow rectangular channel for flow Reynolds number near 20,000. The narrow channel and attendant pump, header tanks and flow instrumentation are portable and designed to allow identical tests in a Concord Microsystems MicroPET P4 pre-clinical PET scanner at the pre-clinical Imaging Suite at the UT Hospital. The PIV data are instantaneous velocity field data, allowing statistics on the flow turbulence to be collected in the Eulerian frame. The PEPT method measures activated particle trajectories in time, corresponding to a Lagrangian measurement. The relationship between the PIV data collected herein, and the anticipated PEPT data is explored to provide a path for validating the performance of the PEPT method for flow measurement. The utility of the PEPT method extends to opaque fluids and flow in complex and opaque flow boundaries. These flow conditions are impossible or technically difficult for optical PIV methods to address. The PEPT method also provides full 4 dimensional particle trajectory data, with temporal and spatial resolution competitive with the most advanced optical PIV methods

A study of rainfall infiltration on slope stability using sand piles to reinforce slopes

Slope instability, predominantly manifested as landslides, stands as one of the most formidable natural hazards, posing significant challenges to sustainability. Prolonged rainfall events are a vital trigger for landslides, with global variations in rainfall patterns primarily attributed to climate change. For instance, on October 3, 2020, the UK experienced its wettest day since 1891, with an average of 31.7 mm of rainfall, illustrating this climatic change. This research aims to investigate the mechanisms of soil slope failure under varying rainfall conditions by combining finite element modeling with physical modeling. The primary objective is to understand the complexities of soil slope failure under different rainfall intensities and durations and to evaluate the effectiveness of sand piles in mitigating failure and reducing damages. The study begins with a numerical analysis using finite element methods, examining various soil slopes with different inclination angles subjected to varying rainfall conditions. A coupled flow-deformation analysis is conducted to unravel the behavior of slopes during rainfall infiltration. Sand piles' length, diameter, spacing, and stiffness are optimized for effectiveness. Next, the optimized parameters from the numerical analysis guide the design and testing of a laboratory-based physical model. This dual approach reveals how slope geometry significantly influences rainfall-induced instability. Gravity forces increase with slope height and inclination, while gentler slopes with longer ponding times, experience more significant rainfall impact. This prolonged infiltration reduces matric suction, diminishing soil shear strength and destabilizing the slope. Conversely, steeper slopes, with shorter ponding times, see more water as surface runoff. The efficacy of sand piles in stabilizing fine soil slopes is highlighted. Sand piles function as both drainage and reinforcement mechanisms, providing effective drainage paths and facilitating the transfer of infiltrated water to the surface as runoff. This reduces pore water pressure and increases matric suction, thereby enhancing soil shear strength and slope stability. The slope was monitored, and soil displacements were measured using a novel approach called the Automated Sensory and Signal Processing System (ASPS). Images captured during the experimental program were processed in MATLAB, applying mathematical equations to extract useful features and categorize slopes based on displacement levels. Low displacement indicated stable conditions, while high displacement signaled potential instability and the need for further intervention. To validate the findings, a case study was conducted on the Azad Pattan Road in Kashmir, Pakistan. This site, consisting of fine silty soil similar to the soil type used in the finite element and lab modeling, provided a real-world application of sand piles. The geology of the slope mirrored the conditions studied in the numerical and physical models, allowing for the practical application of optimized sand pile parameters. In conclusion, this research significantly contributes to understanding slope stability under varying rainfall conditions. By integrating numerical analysis, physical modeling, and the application of sand piles, the study offers a comprehensive view of the factors influencing slope failures and effective stabilization techniques. The case study on Azad Pattan Road in Kashmir further validates these findings, demonstrating practical implications for mitigating landslides in areas prone to slope instability. These insights are invaluable for fortifying resilience against climate change-induced natural hazards