[pt] A alteração de rochas e juntas provoca modificações em suas propriedades, levando à redução da resistência do maciço rochoso e, consequentemente, à redução da segurança das obras de engenharia. O processo de alteração modifica o material e altera seu comportamento geomecânico. Esta pesquisa apresenta os estudos realizados para avaliação do comportamento mecânico das juntas rochosas dos maciços de gnaisse que compõem o circuito hidráulico do Aproveitamento Hidrelétrico Simplício, em função de sua alteração. Foram realizadas compilação e análise de dados obtidos em pesquisas anteriores, para parametrização das juntas em diferentes níveis de alteração. As análises de estabilidade determinísticas mostraram que o processo de alteração das juntas de gnaisse pode reduzir significativamente o fator de segurança do talude, em até metade de seu valor inicial. Além disso, as análises probabilísticas mostraram um aumento da probabilidade de ruptura de aproximadamente 10 por cento entre as classes de alteração estudadas. Os resultados mostram a importância da avaliação do nível de alteração das juntas nos projetos de engenharia. / [en] Rock and joint alteration leads to modifications in their properties, resulting in a reduction of rock mass strength and consequently a decrease in the safety of engineering structures. The alteration process changes the material and alters its geomechanical behavior. This research presents the studies conducted to evaluate the mechanical behavior of rock joints in the gneiss massifs that make up the hydraulic circuit of the Simplicio Hydroelectric Plant due to their alteration. Compilation and analysis of data from previous research were carried out to parameterize the joints at different levels of alteration. Deterministic stability analyses showed that the alteration process of gneiss joints can significantly reduce the slope safety factor by up to half of its initial value. Furthermore, probabilistic analyses revealed an increase in failure probability of approximately 10 percent among the studied alteration classes. The results underscore the importance of assessing the level of joint alteration in engineering projects.

L’objectif de l’étude est d’identifier le comportement des liaisons d’un mécanisme du point de vue des déplacements en fonction des défauts de forme et des jeux. Le sujet est abordé selon une approche théorique et une approche expérimentale.La partie théorique montre la dualité entre les deux concepts utilisés : le domaine jeu et la surface convexe des différences. Elle montre également la typologie des domaines et l’influence des incertitudes de forme sur ces domaines.En parallèle, un dispositif expérimental est développé. Il permet, non seulement, de réaliser la mesure des déplacements dans la liaison avec l’exactitude nécessaire, mais aussi, de valider les résultats par une simulation de l’assemblage à partir de la mesure 3D des surfaces en contact. L’expérimentation porte sur plusieurs couples de surfaces comportant des défauts de forme de différents types. L'influence d'un chargement mécanique est étudiée afin de quantifier les déformations locales de surfaces de contact et l'évolution des écarts de position entre les pièces. / The aim of the study is to identify, in terms of displacements, the joint behavior of a mechanism in function of form defects and gaps. Two approaches are proposed : a theoretical approach and an experimental one.The theoretical part presents the duality between the two concepts used in the experimental approach : gap hull and convex difference surface. It outlines also the typology of gap hulls and the influence of the form uncertainties on gap hulls.In parallel, an experimental device is developed. It allows, not only, to carry out the measure of displacements in the joint with the necessary accuracy, but also, to validate the results by an assembly simulation from the 3D measurement of the surfaces in contact. The experimentation involves several pairs of surfaces with different types of form defects. The influence of mechanical loads is studied in order to quantify the local deformation of the surfaces in contact and the evolution of location deviations between these surfaces.