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With regards to the composition of natural rocks including voids or pores, deformation behavior is strongly affected by variation in porosity. By using a statistical damage-based approach, the characteristics of strain softening and hardening under the influence of voids and volume changes are investigated in the present paper. Suppose that a rock consists of three parts: voids, a damaged part, and an undamaged part. The effects of voids and volume changes on rock behavior are first analyzed through determination of the porosity and an associated damage model is then developed. Later, a statistical evolution equation describing the influence of the damage threshold on the propagation condition of rock damage is formulated based on measurement of the mesoscopic element strength. A statistical damage constitutive model reflecting strain softening and hardening behavior for rocks loaded in conventional triaxial compression is further developed and a corresponding method for determining the model parameters is also provided. Theoretical results of this proposed model are then compared with those observed experimentally. Finally, several aspects of the present constitutive model, which affect the relevant behavior of rocks, are particularly discussed. Key words: geotechnical model, strain softening and hardening, damage, statistics, porosity, volume change. Dans le cas de roches naturelles incluant des vides ou des pores, le comportement en deformation est fortement affecte par la variation de porosite;. Dans cet article, les caracteristiques d'ecrouissage et d'anti-eicrouissage, en relation avec les vides et les variations de volume, sont investigueees a l'aide d'une approche statistique basee sur les dommages. L'effet des vides et des variations de volume sur le comportement de la roche est analyse premierement par la determination de la porosite, ensuite un modele de dommages associes est deeveloppee. Par la suite, une equation d'evolution statistique, qui deecrit l'influence du seuil de dommage sur les conditions de propagation des dommages dans la roche, est formuleee selon les mesures de resistance mesoscopique des elements. Un modele constitutif statistique de dommages, qui reflete les comportements en ecrouissage et anti-eecrouissage de roches chargees en compression triaxiale conventionnelle, est developpe, ainsi qu'une methode permettant de determiner les parameetres du modele. Les resultats obtenus a l'aide du modele proposee sont compares aux resultats experimentaux. Pour terminer, plusieurs aspects du modele constitutif qui influencent le comportement des roches sont discutes de facon particulieere. Mots-cles: modele geotechnique, ecrouissage et anti-ecrouissage, dommage, statistique, porosite, variation de volume. [Traduit par la Redaction], Introduction A thorough understanding of deformation behavior in rocks is an essential and paramount requirement for analysis and design of rock engineering, and the correlation between load and deformation is [...]