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Altération par le gel des massifs rocheux : Etude expérimentale et modélisation des mécanismes de génération des contraintes dans les fissures

Abstract : Stone and rock falls bring about problems related to land management in mountainous areas. Yet, the temporal assessment of the risk of rupture in blocks requires a kinetic description of weathering phenomenon. In the case of limestone cliffs in mountainous areas, it can be estimated that the dominant weathering process lies in cracks propagation due to freezingthawing cycles. This freezing-thawing mechanism within a rock matrix was reproduced in laboratory experiments with notched specimens. Experimental results allowed us to establish a model for the stresses due to frost. This stress model, along a crack inner wall, exhibits a maximum, which spreads more and more deeply along with spending time, until a limit, which is intrinsic to the material. Actually, the generated stress results as a balance between the confining pressure induced by the ice front spreading deeply in the crack and the water leakage in the porosity network in the vicinity of the crack. It is thus strongly dependent on the crack geometry and on the porous network features of the rock. An analytical assessment of the stress intensity factor at the crack bottom, by using the model established for the stress, was carried out. It matches the possibility to initiate a rupture according to linear failure mechanics laws. Microscopic observations of the crack evolution throughout the freezingthawing cycles show a progressive and heterogeneous rupture of the limestone. The crack propagation was simulated numerically. This simulation gave encouraging results, as it brought up to light key-elements which could be used to establish a predictive model for the failure of a rock mass subject to freezing-thawing cycles.
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Marion Bost. Altération par le gel des massifs rocheux : Etude expérimentale et modélisation des mécanismes de génération des contraintes dans les fissures. Matériaux et structures en mécanique [physics.class-ph]. Ecole des Ponts ParisTech, 2008. Français. ⟨tel-00360420⟩

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