214 publications from this institution
Most earth-dam failures are mainly due to seepage, and an accurate assessment of the permeability coefficient provides an indication to avoid a disaster. P
The shear strength of discontinuities plays a key role in the stability of rock masses, particularly in the case of analyzing the sliding stability of the rock foundations of gravity dams. This paper proposes a methodology for analyzing the spatial variability of shear strength along the joints of rock mass, based on the input parameters of the Barton and Choubey's model. The aim of this approach is to evaluate the reduction of the variance of the parameters involved at full-scale by identifying a deterministic trend varying in depth and a spatial correlation calculated from a variographic analysis. An advantage of this methodology is to use a simple experimental protocol (a laser profilometer, a portable shear test apparatus and a concrete sclerometer), which generates large sets of shear strength properties for assessing their spatial variability. The methodology is illustrated in the case of the rock foundation of a concrete gravity dam. Analysis of the spatial variability conducted for this case study led to a significant reduction of the variance of the variable analyzed. The advantage of this method is demonstrated through the evaluation of the probability of failure performed in a study of this structure's stability. Taking variance reduction into account in the case study led to significantly reducing the probability of failure assessed through a reliability analysis.
Forecasting flood characteristics (e.g., water levels and velocity) is a growing concern due to climate change. It is therefore necessary to consider the stability conditions of earthen levees used to mitigate floods during a flood risk assessment. This technical note presents a method to assess probabilistic flood hazard that takes into account levee failures, for a levee located along Etobicoke Creek in Toronto, Canada. We compute flood scenario probabilities resulting from multiple flood scenarios that accounts for both the levee failures across the length of the levee, and different levee-failure mechanisms (e.g., backward erosion and overtopping). Then, for each location of the flooded area, we compute a cumulative flood exceedance probability curve for flood depth and velocity. This method provides a flood-hazard map (depth and velocity) for a given probability and probabilistic maps for given values of depth or velocity.
No abstract is provided for this article.
No abstract is provided for this article.
Studies carried out to analyse the risks of levees must include an evaluation of the probabilities of occurrence of different failure mechanisms (overflow, internal erosion, sliding and scouring).The probabilistic quantitative evaluation of these mechanisms remains difficult due to often insufficient input data, the natural variability of the materials, structures of very long length, the availability of mechanical models for certain failure mechanisms, and the random nature of the stresses involved.This makes it necessary to call for expert judgement to evaluate the probabilities of failure.However, expert judgement is generally associated with a qualitative and subjective dimension, and it comprises biases liable to impair the capacities of an expert to elicit their evaluations.This article proposes an approach to processing expert judgement that includes the modalities of Individual expert Elicitation, Calibration, Aggregation, and Debiasing of expert judgement (IeCAD).This IeCAD approach has been developed for river levees in view to correcting biased expert evaluations in the case of evaluating the failure probability of structures.
No abstract is provided for this article.
No abstract is provided for this article.
Mountain reservoirs are hydraulic structures established in recreational mountain resorts designed to provide a water reserve mainly used for the production of artificial snow. Their siting in high-altitude zones makes them highly specific reservoirs subjected to and inducing risks and impacts on their human and ecological environment. Based on in-depth bibliographic and field research, Cemagref has launched a study on mountain reservoirs. The present article aims to establish the current state of the risks related to mountain reservoirs and their impacts on the environment, placing the development of mountain reservoirs in their societal, social, and environmental contexts. It will then develop mountain reservoir risks and impacts, focusing on the specific risks and uncertainties to which these structures are exposed, and the different environmental impacts related to the construction and management of these reservoirs.
RESUME : Les digues de protection contre les inondations sont des ouvrages a grands lineaires dont la performance est tres variable longitudinalement. Lors de crues, leur rupture meme tres localisee peut entrainer des inondations catastrophiques. Dans cette communication, nous proposons l’identification, la construction et la mise en œuvre d’une demarche d’aide a la decision permettant le decoupage des lineaires de digues en troncons homogenes et leur tri par niveau de performance. Nous proposons la formulation d’une methode de type critere unique de synthese et son l’application a des cas d’etudes.
Accident statistics for embankment dams show that internal erosion is a major cause of incidents involving these structures. However, internal erosion is a complex process and remains difficult to assess probabilistically. This technical note presents a probabilistic analysis of internal erosion for an existing embankment dam. The spatial variability of soil properties is modeled using random field theory and incorporated into a finite element seepage analysis. The probabilistic results yield spatial distributions of the means and variances of key hydraulic parameters, such as flow velocity and hydraulic gradient. By applying initiation criteria for three internal erosion mechanisms—backward erosion, suffusion, and contact erosion—the safety of the dam is assessed through the initiation probability ( P f ), derived from the probability distribution of the factor of safety (FoS) for each mechanism. This approach is used to evaluate the probability of internal erosion initiation across different zones of the dam. The results can then be used for risk analysis studies for embankment dams by assessing potential failure scenarios due to internal erosion. • Spatial variability of hydraulic properties modeled via random fields. • Coupled finite element seepage analysis with geostatistical inputs. • Initiation probability estimated for three internal erosion mechanisms. • Real-case application enhances dam safety risk assessment.
Modelling concrete shear strength is the main difficulty in probabilistic reliability analysis of gravity dam structural safety. The main reason arises from the lack of test data on the parameters. This paper proposes a procedure for probability modelling of Roller Compacted Concrete (RCC) gravity dam shear strength based on all tests performed during dam construction and all available data. The procedure embraces several methods: statistical analysis of RCC density, analysis of scatter at different spatial scales, data unification, and a physical formulation of the RCC intrinsic curve. A case study demonstrates the applicability of the procedure on an existing RCC gravity dam. The probability distributions obtained are incorporated into the formulation of the shear strength limit state using a first order reliability method and Monte Carlo simulations.
This paper presents a robust observer based on redundancy computing EMF on 2-axis rotor oriented reference frame. Driving sensorless synchronous machine is presented in 3 steps. The first is a stalling phase to avoid wrong rotation whatever the initial rotor position is. The second step is a calibration phase, to estimate accurately the electrical parameters of the drive. So using the 2 first step, finally we control the sensorless drive by estimating EMF, velocity and position which are quite close to reality only by voltages and currents measurements.
No abstract is provided for this article.
: A computational methodology dedicated to embankment dam performance assessment has been designed and implemented. The model's inputs are the whole set of available information and data: visual observations, monitoring measurements, calculated data, and documents related to design and construction processes. First, a formal grid is proposed to structure the inputs. It is composed of six fields: name, definition, scale, references as anchorage points on the scale, and spatial and temporal characteristics. Structured inputs are called indicators. Second, an indicator aggregation method is proposed that allows obtaining not only the dam performance but also the assessment of its design and construction practices. The methodology is illustrated mainly with the internal erosion mechanism through the embankment, but results concerning other failure modes are also provided. An application of the method for monitoring dams through time is given.
