Conception d'un modèle de laboratoire d'un évacuateur de crue pour étudier l'érosion des masses rocheuses

L’érosion hydraulique du massif rocheux d’un évacuateur de crues résulte de l’action de l’eau sur celui-ci, un phénomène évalué par différentes méthodes en utilisant la corrélation entre la force érosive de l’eau et la capacité d’une masse rocheuse à y résister. L’érosion se produit lorsque la force érosive de l’eau dépasse la capacité de résistance des formations rocheuses. La résistance d’un massif rocheux est alors estimée par différents indices ainsi que la force érosive de l’eau. Avec ces indices et sur la base de certaines études de laboratoire, des méthodes d’évaluation d’érosion hydraulique ont été développées. Cependant les résultats obtenus par ces méthodes comportent plusieurs incohérences, notamment l’utilisation de certains paramètres hydrauliques et géomécaniques jugés non pertinents dans la détermination des forces en cause du processus d’érosion hydraulique. Le contenu de ce mémoire présente de nouvelles avancées dans l’investigation du phénomène d’érosion hydraulique. Notamment, l’identification des incohérences liées aux anciennes méthodes d’évaluation de l’érosion hydraulique à travers une revue de littérature, à la suite de laquelle nous essaierons de développer une méthode permettant la détermination de l’applicabilité des paramètres hydraulique dans le processus d’érosion. De nouvelles solutions sont donc proposées dans le but de mieux caractériser le processus d’érosion hydraulique, dont le développement d’une nouvelle méthode de détermination du volume exact des blocs de roche dans un massif rocheux. La conception d’un modèle physique réduit d’évacuateur de crue a également été nécessaire dans le but de pouvoir de caractériser le phénomène d’érosion. Ce modèle regroupe tous les paramètres considérés comme pertinents dans le processus d’érosion et sa représentativité dans l’étude de l’interaction entre la force érosive de l’eau et les paramètres géomécaniques a été validée à travers des essais d’écoulement. Les paramètres hydrauliques considérés dans la conception du modèle sont le débit, la vitesse d’écoulement, la pression d’eau et la pente du canal. Concernant les paramètres géomécaniques, nous avons le volume des blocs, la résistance en cisaillement des joints, la disposition des blocs par rapport à la direction de l’écoulement, l’ouverture des joints, l’altération des joints et la nature de la surface du canal potentiellement érodable

Identification of Hydraulic Parameters Influencing the Hydraulic Erodibility of Spillway Flow Channels

The rock mass erosion of dam spillways, a phenomenon involving the interaction between the hydraulic load of water and the capability of the rock mass to resist its destruction, remains a critical safety issue. The erosion resistance of a rock mass can be estimated through several erodibility indices, including those of Kirsten, Pells or Bollaert. Several indices have been developed to link rock resistance to the hydraulic parameters of water, i.e., the hydraulic load applied on a rock mass. The developed indices use the average flow velocity, the average shear stress on the bottom of the flow channel, the stress applied to the internal joints of fractured rock mass, the dynamic impulse force, and the power dissipation of water to represent the erosive force of water. From these indices, several methods of assessing hydraulic erosion have been developed, and all use the threshold line concept. Nonetheless, several uncertainties are associated with these methods. This paper presents and discusses the various means of calculating the erosive force of water as a hazard parameter for predicting potential rock erosion. The representativeness of these approaches is also discussed, and we clarify nuances associated with each method. We then provide guidelines for future research aimed at improving estimates of the erosive force of the water within spillway flow channels

Identification of hydraulic parameters influencing the hydraulic erodibility of spillway flow channels

The rock mass erosion of dam spillways, a phenomenon involving the interaction between the hydraulic load of water and the capability of the rock mass to resist its destruction, remains a critical safety issue. The erosion resistance of a rock mass can be estimated through several erodibility indices, including those of Kirsten, Pells or Bollaert. Several indices have been developed to link rock resistance to the hydraulic parameters of water, i.e., the hydraulic load applied on a rock mass. The developed indices use the average flow velocity, the average shear stress on the bottom of the flow channel, the stress applied to the internal joints of fractured rock mass, the dynamic impulse force, and the power dissipation of water to represent the erosive force of water. From these indices, several methods of assessing hydraulic erosion have been developed, and all use the threshold line concept. Nonetheless, several uncertainties are associated with these methods. This paper presents and discusses the various means of calculating the erosive force of water as a hazard parameter for predicting potential rock erosion. The representativeness of these approaches is also discussed, and we clarify nuances associated with each method. We then provide guidelines for future research aimed at improving estimates of the erosive force of the water within spillway flow channels

A Reduced-Scale Physical Model of a Spillway to Evaluate the Hydraulic Erodibility of a Fractured Rock Mass

The hydraulic erosion of the rock mass within dam spillways must be considered when assessing the stability of dam infrastructures. As this erosion results from the interaction between water and the rock mass, commonly applied methods to evaluate this phenomenon use the notion of a threshold line, a correlation between the water’s erosive force and the resistance of the rock mass against erosion. These methods are empirical or semi-empirical, and they have limitations regarding the characterization of this phenomenon. These methods are based on specific hydraulic and rock mass parameters, including a number of parameters that are irrelevant to the erosion process; thus, there is a need to upgrade the existing methods or to seek new solutions to characterize hydraulic erosion. We present a laboratory-scale physical model to determine the effects of rock mass parameters on erosion. This model is designed to determine individual and interactive effects of several hydraulic and rock mass parameters on erosion, including joint opening, block size, joint shear strength, and the nature of potentially erodible surfaces, as well as water pressure (static and dynamic), variations of flow rate and velocity, and channel roughness

Advancements in rock block volume calculation by analytical method for geological engineering applications

The shape, the volume, and the distribution of the rock blocks represent important geomechanical factors of a rock mass behavior in engineering works. Several methods have been developed for estimating these parameters, including numerical models, as well as analytical and empirical methods. However, their determination in actual in-situ conditions can be quite challenging. The existing analytical methods show limitations in determining the in-situ rock blocks volume. Numerical models provide more reliable estimates of these parameters, but they are not accessible to all, and they require a good working knowledge. Increasing the accuracy of existing analytical methods, or developing more reliable and accessible methods, are more realistic approaches to obtain better estimates of rock block volumes. This paper presents a new method to obtain more accurate estimates of in-situ rock block volume. The method is developed for rock a mass consisting of three persistent joint sets, each set having constant spacing and orientation values. It is based on vector products to obtain exact block volumes, an improvement as compared to previous methods. The volumes of the rock blocks are calculated through the multiplication of the blocks’ edge vector. The results of the developed equation are validated with the output of numerical simulations using 3DEC version 7.0 software, and the results indicate that the developed method makes it possible to determine in-situ rock block volume more reliably than the existing methods