A method to determine relevant geomechanical parameters for evaluating the hydraulic erodibility of rock

Among the methods used for evaluating the potential hydraulic erodibility of rock, the most common methods are those based on the correlation between the force of flowing water and the capacity of a rock to resist erosion, such as Annandale's and Pells' methods. The capacity of a rock to resist erosion is evaluated based on erodibility indices that are determined from specific geomechanical parameters of a rock mass. These indices include unconfined compressive strength (UCS) of rock, rock block size, joint shear strength, a block's shape and orientation relative to the direction of flow, joint openings, and the nature of the surface to be potentially eroded. However, it is difficult to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock. The assessment of eroded unlined spillways of dams has shown that the capacity of a rock to resist erosion is not accurately evaluated. Using more than 100 case studies, we develop a method to determine the relevant geomechanical parameters for evaluating the hydraulic erodibility of rock in unlined spillways. The UCS of rock is found not to be a relevant parameter for evaluating the hydraulic erodibility of rock. On the other hand, we find that the use of three-dimensional (3D) block volume measurements, instead of the block size factor used in Annandale's method, improves the rock block size estimation. Furthermore, the parameter representing the effect of a rock block's shape and orientation relative to the direction of flow, as considered in Pells' method, is more accurate than the parameter adopted by Annandale's method

Determining relative block structure rating for rock erodibility evaluation in the case of non-orthogonal joint sets

The most commonly used method for assessing the hydraulic erodibility of rock is Annandale’s method. This method is based on a correlation between the erosive force of flowing water and the capacity of rock resistance. This capacity is evaluated using Kirsten’s index, which was initially developed to evaluate the excavatability of earth materials. For rocky material, this index is determined according to certain geomechanical factors related to the intact rock and the rock mass, such as the compressive strength of intact rock, the rock block size, the discontinuity shear strength and the relative block structure. To quantify the relative block structure, Kirsten developed a mathematical expression that accounted for the shape and orientation of the blocks relative to the direction of flow. Kirsten's initial concept for assessing relative block structure considers that the geological formation is mainly fractured by two joint sets forming an orthogonal fractured system. An adjusted concept is proposed to determine the relative block structure when the fractured system is non-orthogonal where the angle between the planes of the two joint set is greater or less than 90°. An analysis of the proposed relative block structure rating shows that considering a non-orthogonal fractured system has a significant effect on Kirsten’s index and, as a consequence, on the assessment of the hydraulic erodibility of rock

Contribution à l'instrumentation des ouvrages en béton application des fibres optiques pour la mesure des déformations internes

La nécessité de surveiller les ouvrages de génie civil, plus spécialement les grands barrages, ne fait maintenant plus de doute, autant parmi les concepteurs que les gestionnaires. Le vocable « sécurité des barrages » fait maintenant partie du vocabulaire des techniciens, ingénieurs et administrateurs et il intègre plusieurs aspects spécifiques: la sécurité du public, l'environnement et l'économie. Aussi, les conséquences de la rupture ou de l'endommagement d'un barrage de grande envergure sont des pertes, plus ou moins considérables, à tous les paliers énumérés auparavant. Dans Ie cas des barrages, la modification de l'état de la structure, souvent liée au vieillissement du béton, doit être suivie afin de garantir la sécurité de l'ouvrage La technologie des capteurs a fibre optique est actuellement en plein essor. Cette technologie est particulièrement intéressante puisqu'elle permet d'installer des capteurs extrêmement efficaces a des endroits jusqu'à maintenant inaccessibles. La sensibilité des capteurs et la rapidité de lecture permettent d'envisager, entre autres, la mesure des faibles déformations et des comportements cycliques. En ce qui a trait a l'instrumentation géotechnique et structurale, cette technologie laisse entrevoir de nombreuses possibilités.Abstract: Surveillance of large engineering structures, especially large dams, is of great concern among designers as well as for managers. The expression""dam security"", now common for dam technicians, engineers and managers, includes many specific aspects: public security, environment protection and economy. Also, the consequences of large dam failure or damaging are losses in all aspects already mentioned. Keeping track of the changing state of dams, often related to the aging of structure concrete, is quite important regarding security aspects. Fiber optic sensors technology is expanding very rapidly. The particular interest of this technology is the possibility to install efficient sensors at locations difficult to reach. The sensitivity of these sensors and their fast response allow, among other things, to measure small strains and cyclic behavior. Regarding geotechnical and structural instrumentation, this technology gives rise to many perspectives. Among many research avenues, development of a simple internal strain detection probe for specific application in concrete dam monitoring is proposed. This research theme is a continuation of the Cylindre instrumenté de l'Université de Sherbrooke (CIUS) development. Application of fiber optics and real time monitoring system to dam instrumentation could be hold as the originality of the present work. Actually, working on the design of small fiber optic and vibrating wire strain measuring probe is the main task. Installed in dams, this type of probe would allow an accurate real-time monitoring of the global or local behaviour of the structure and also, eventually, remote monitoring. Design of the proposed device first begins with a validation, in laboratory and on site, of the new fiber optic sensor technology for concrete instrumentation. Results show that the embedded Fabry-Pérot sensors allows to monitors internal strains in concrete because the modification of the properties of the surrounding concrete is negligible. Temperature is of less effect on the embedded sensor and correction factors are unnecessary. Finally, development of an internal strain measurement probe is possible with this new type of strain gauge

Determining rock erodibility parameter « relative block structure » for non-perpendicular hydraulic flow

The most commonly used method for assessing the hydraulic erodibility of rock is the Annandale’s method. This method is based on a correlation between the force of flowing water and the capacity of rock resistance. This capacity is evaluated using the Kirsten’s index which was initially developed to evaluate the excavatability of earth materials. This index is determined according to certain geomechanical factors, such as the compressive strength of intact rock, the rock block size, the discontinuities shear strength and the relative block structure. This last characteristic represents the required effort to erode the rock and, it can be quantified considering the shape and orientation of the blocks. To determine the relative rock structure in the field, the dip and dip direction of closer spaced joint set, as well as the ratio of joints spacingare required. It is found that the Kirsten’s concept can be applied only when the direction of flow is perpendicular to the strike of closer spaced joint set. Adjustments are introduced to Kirsten's initial concept concerning the relative block structure parameter. Thus, two equations are proposed which were used to propose a rating for the relative block structure parameter for a case example with non-perpendicular flow. La méthode la plus utilisée en pratique pour l’évaluation de l’érodabilité hydraulique du roc est celle d’Annandale. Celle-ci se base sur une corrélation entre la force érosive de l’eau et la capacité de résistance du roc. Cette capacité est évaluée à l'aide de l’indice de Kirsten initialement développé pour évaluer l’excavabilité des matériaux. Cet indice est déterminé en fonction de certaines caractéristiques géomécaniques telles que la résistance matricielle de la roche intacte, la taille des blocs, la résistance au cisaillement des discontinuités et la structure relative des blocs. Cette dernière caractéristique représente l’effort requis pour que le roc soit érodé et, elle peut être quantifiée en considérant la forme et l’orientation des blocs. En pratique, elle se détermine en fonction du pendage et la direction du pendage de la famille des joints les moins espacés, ainsi que le ratio d’espacement des joints. Il est observé que le concept de Kirsten n’est valide que lorsque l’écoulement est perpendiculaire à l’azimut de la famille des joints les moins espacés. Des ajustements sont introduits sur le concept initial de Kirsten concernant la structure relative des blocs. Ainsi, deux équations sont proposées et utilisées pour générer des pondérations de la structure relative des blocs pour un exemple de cas avec un écoulement nonperpendiculaire

Novel 3D Pixel Sensors for the Upgrade of the ATLAS Inner Tracker

The ATLAS experiment will undergo a full replacement of its inner detector to face the challenges posed by the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). The new Inner Tracker (ITk) will have to deal with extreme particle fluences. Due to its superior radiation hardness the 3D silicon sensor technology has been chosen to instrument the innermost pixel layer of ITk, which is the most exposed to radiation damage. Three foundries (CNM, FBK, and SINTEF), have developed and fabricated novel 3D pixel sensors to meet the specifications of the new ITk pixel detector. These are produced in a single-side technology on either Silicon On Insulator (SOI) or Silicon on Silicon (Si-on-Si) bonded wafers by etching both n- and p-type columns from the same side. With respect to previous generations of 3D sensors they feature thinner active substrates and smaller pixel cells of 50 × 50 and 25 × 100 µm2. This paper reviews the main design and technological issues of these novel 3D sensors, and presents their characterization before and after exposure to large radiation doses close to the one expected for the innermost layer of ITk. The performance of pixel modules, where the sensors are interconnected to the recently developed RD53A chip prototype for HL-LHC, has been investigated in the laboratory and at beam tests. The results of these measurements demonstrate the excellent radiation hardness of this new generation of 3D pixel sensors that enabled the project to proceed with the pre-production for the ITk tracker.publishedVersio

Amélioration de la détermination des propriétés de résistance de l'interface béton-rocher et des discontinuités des fondations rocheuses des barrages poids

CIGB 2018, 26è Congrès des Grands Barrages, Vienne, AUTRICHE, 01-/07/2018 - 07/07/2018La détermination des caractéristiques mécaniques régissant la stabilité d'un barrage existant peut s'avérer complexe notamment en ce qui concerne les discontinuités présentes en fondation et à l'interface barrage-fondation. Ces caractéristiques sont la résistance à la traction, la cohésion et l'angle de frottement. Fort de ce constat, IRSTEA et EDF ont lancé des travaux de recherche ces dernières années de manière d'une part à créer des données utiles à la compréhension des mécanismes de rupture et d'autre part à proposer des méthodologies d'estimation des caractéristiques mécaniques utilisables directement par l'ingénierie. Le présent article donne les principaux résultats des essais de traction et de cisaillement sur des interfaces béton-rocher. Ces résultats pourraient faire l'objet d'échange et de partage avec les ingénieries intéressées par le sujet. L'article présente également des méthodologies de détermination des caractéristiques de discontinuités rocheuses en cisaillement ainsi que des caractéristiques de résistance à la traction de l'interface béton-rocher. Des perspectives sont proposées quant à de futures actions de recherche prometteuses telles que la caractérisation de la cohésion apparente des discontinuités rocheuses et l'estimation de la géométrie du contact barrage-fondation par des méthodes non-destructives