Claude Bacconnet

Probability-based assessment of dam safety using combined risk analysis and reliability methods – application to hazards studies

Dam safety assessment is a major challenge for engineers specialising in hydraulic works. It is now standardised in regulations providing for hazards studies using probability-based risk analysis procedures. Dam safety probability-based assessment includes two key scientific issues: the modelling of complex mechanisms that occur within the works, and a probability-based assessment of structural safety. This paper introduces a combined application of risk analysis and dam reliability methodologies. This combination required the completion of our work on the adaptation of risk analysis methods to dams, and on the probability-based modelling of strength and loading input data for a reliability-based analysis. These methodologies are then implemented as part of a hazards study on a roller-compacted-concrete gravity dam.

Probability modelling of shear strength parameters of RCC gravity dams for reliability analysis of structural safety

ABSTRACT 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.

On the loading/shear strength coupling in the probabilistic formulation of the limit-state in shear for gravity dams

ABSTRACT 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.

Study on a semi-probabilistic method for embankment hydraulic works: Application to sliding mechanism

ABSTRACT Both in France and at the global level, hydraulic works have remained excluded from semi-probabilistic regulations. As far as embankment hydraulic works are more specifically concerned, there are no formal rules for their design. In this context, the French Commitee on Large Dams initiated a research project to define a semi-probabilistic limit-state method for the design of embankment hydraulic works. This paper accounts for the work done over two years. It determines the position of embankment hydraulic works in relation to Eurocode 7. It briefly outlines the suggested semi-probabilistic limit-state method and focuses on the sliding limit-state. Applying the method to a pseudo-homogenous dam helps comparing the standard deterministic practice, the Eurocode 7-based approach and the developed semi-probabilistic method.

Modulus Estimation of Surrounding Soils of Underground Structures in Service

Most underground structures in urban areas were built several decades ago and require diagnosis and maintenance to ensure their longevity. To ensure that diagnosis is as complete as possible, it is necessary to evaluate their state on three levels: structure lining, contact interface (soil/structure), and surrounding soil. However, at present, there is no fully appropriate technique for characterizing the parameters of surrounding soils and their variability in situ. This paper deals with a less invasive methodology used to obtain an estimation of the elasticity modulus of the surrounding soil of underground structures in service. The combined use of a dynamic lightweight penetrometric test (PANDA) and geoendoscopic tests permits estimating the deformation modulus of soils from the tip resistance (qd) for a given material and from relations established for different soil models. The paper first presents the complete methodology proposed for in situ soil characterization, then the experimental work carried out in the laboratory for obtaining the relations linking the penetration tip resistance to the elastic modulus for four soil models and for different density and moisture conditions. Finally, the performance and adaptability of the methodology for estimating soil-deformation modulus and its variability is demonstrated by in situ testing campaigns in the Paris subway network.

Methodology for Confirming the Micropiles Service Performance Based on Dynamic Tests

AbstractThe uplift load test is the most widely used technique for assessment of the performance of micropiles. Although this static load test is easy to perform and interpret, it is expensive, slo...

Liquefaction potential of sand tailings dams evaluated using a probabilistic interpretation of estimated in-situ relative density

In Chile, sand tailings dams represent the most common deposits of mining residues. These structures present a potential risk in terms of mechanical instability due to their potential susceptibility to seismic liquefaction. In order to manage these risks, it is necessary to take a probabilistic approach, thus accounting for inherent variability of material properties. However, in practice, implementing such an approach is impeded by the difficulty of acquiring and managing the data to be used in the reliability calculations and is conditioned by the relevance of the probabilistic models chosen to represent this variability. This paper proposes a method for onsite determination of the tailings relative density (DR%), and its variability, using dynamic penetration tests. This method was applied to a typical Chilean sand tailings dam, and proposes a single model for all such tailings dams by associating a probability law to the variation of DR%. Finally, the validity of this approach is demonstrated by performing a reliability calculation of liquefaction potential (which is the main cause for the failure of this type of structure in this country) for a particular tailings dam.