No abstract is provided for this article.
No abstract is provided for this article.
This paper proposes a methodology to take into account of the dependence between hydraulic loading and shear strength in a probability-based procedure for assessing the gravity dam structural safety. This is a major point in a probability-based approach where extreme loadings are a determining factor of dam reliability. The proposed approach uses a parabolic formulation of concrete shear strength. It aims at providing a better representation of the intrinsic curve for normal stress lower levels that might develop in the dam upstream area under extreme hydrostatic loading conditions. Based on the FORM method and on Monte Carlo simulations, a case study shows how relevant the proposed method is and the impact thereof on the results of a reliability analysis completed for an existing gravity dam.
No abstract is provided for this article.
Based on a previous experimental study that we conducted on granite joint replicas including thirty direct shear tests, this article proposes to integrate the joint roughness in the Mohr-Coulomb shear behaviour model (MC). The model integrates joint roughness into constitutive stress-displacement relationships describing mechanical behaviour of rock joint. The shear strength of rock joint is assessed by the MC shear criterion that takes into account the apparent cohesion. This MC model integrating rock joint roughness component is validated against other experimental results from the literature. It is able to accurately predict the peak shear strength of an unbounded rock joint with an average relative error of 7.9%. It is finally used to assess the role of joint roughness on the shear behaviour of a gravity dam foundation.
No abstract is provided for this article.
Cemagref and ISL consulting engineers produced for Nîmes city (France) a reliability study concerning a hydraulic works system, composed of several dams, singular civil works, canals and collectors networks, and intended to ensure protection against floods. This study constitutes one of the first quantitative reliability studies of a hydraulic works system realized in France. This article presents the step and the methodologies used in a reliability quantitative analysis. The methodological developments are illustrated all along the text through this remarkable application.
Les racines d’arbre sont reconnues comme un danger lorsqu’elles poussent dans les structures en remblai d’ouvrages hydrauliques, et notamment des digues. Deux principaux risques sont associes a la presence d’arbres sur ces ouvrages : l’erosion interne liee au developpement racinaire dans le corps de digue ou sa fondation et l’erosion externe relative au deracinement potentiel de grands arbres sous l’effet du courant ou du vent. L’objectif des travaux de these, est d’elaborer des methodes de prospection non destructives permettant de reperer et evaluer les developpements racinaires dangereux dans les ouvrages hydrauliques. Pour cela, une methodologie couplant une approche experimentale et de modelisation est etablie dans le but de caracteriser le systeme racinaire. / Roots are recognized as an environmental hazard when growing in hydraulic earth structures, especially dikes. Trees’ rooting in earth dikes generates two types of risks: internal erosion due to root development in earth embankments or their foundation, and external erosion (slopes and crest) which is often related to trees uprooting by the effects of currents or wind. The aim of the beginning thesis, subject of this paper, is to elaborate non-destructive prospection methods able to detect and evaluate dangerous tree roots growing in dike or dam body. To this end, we have to design a methodology including non-destructive methods and geophysical models in order to characterize the root system. Several geophysical methods are often used for exploration of soil. Nevertheless, given the complex variety of bank and soil properties composing earth dikes, these non destructive methods have to be adapted and improved to detect and localize woody roots in these specific conditions.
Click to increase image sizeClick to decrease image sizeThe use of gabions in the small dams in the Sahel regions of Africa is quite common, they are used in flood spillways in which the gabion weirs are usualtechniques. Indeed, apart from a good mechanical stability and a high level of resistance to flood flows, gabion weirs enable a large amount ofpredissipation of water energy before the stilling basin. In the present state of the technique the right dimensions for this type of structure are not well known. To define energy dissipation on the shoulders a systematic study of the standardized wasteways from 3 to 5 m high, for a flow rate of up to 3 m3/s per meter width, has been carried out on scale models on 1/5 scale.It has enabled the amount of energy dissipation to be quantified and enabled determination of dimensioning parameters for the stilling basin. The results obtained lead to a saving of 10 to 30 % over the length of the stilling basin compared to the lengths obtained with the methods used up to present. Moreover, we also wished to classify the flows on the shoulders and define the phenomena observed during the different hydraulic regimes.
Expert judgment plays an essential role in assessing the safety of levees, since these very long structures are generally old, few data are available for them, and they are subject to complex failure mechanisms. Expert judgement is required to assess the failure probabilities of levees when carrying out risk analysis studies. However, expert judgement is subject to biases that are highly likely to impair the quality of the probabilistic assessments obtained. This article presents a method for reducing biases in expert opinion, illustrated by its application to the case of an existing levee. Initially, the method comprises the calibration of the opinions of a panel of six experts based on the results of a quantitative analysis applied to 30 levee cross-sections for which numerical calculations were performed. It then proposes a procedure to debias expert assessments using bias correction coefficients. Regarding its application, the assessments made by the experts were debiased for 30 calibration variables. The correction coefficients obtained were then applied for the assessment of 10 variables of interest. The results show a significant reduction of biases, associated with a readjustment of the uncertainty intervals given by the experts.
Considering risk analysis in the industrial context we first present the main concepts dealing with risk and its analysis. Secondly we build up a synthesis of the different existing approaches: internal methods including physical and functional modelling, external methods including statistical approach and expertise. For each of them, we list the main applications in civil engineering and we develop their use in the peculiar case of dams.
Gabions are a common construction material in the African Sahel and elsewhere, especially for spillways. Stepped gabion spillways are structurally stable, resistant to water loads, and efficient energy dissipators, but there are no clear design rules to date. One‐fifth‐scale model tests representing 3–5 m high standard prototypes discharging up to 3m3⋅s-1⋅m-1 enabled us to establish quantified energy‐dissipation criteria and efficient stilling‐basin design rules, saving 10–30% on basin length as compared with current methods. The different types of flow over the stepped face are also described and analyzed: isolated nappe flow, partial nappe flow, and skimming flow. From a technical point of view, stepped gabion spillways can withstand flows up to 3m3⋅s-1⋅m-1 without great damage, if setting of gabions complies faithfully with the code of practice. Some advice is given on preventing gabion deformation.
