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Abstract The excavation in rocks is mainly an unloading behavior. The characteristics of strength and deformation failure of rocks are researched；propagation evolvement and mechanical mechanism of cracks are discussed under two unloading stress paths based on physical model test of fissured rocks. The strength and deformation failure of rocks，propagation of cracks are obviously impacted by the included angle of cracks with unloading direction and combination between cracks. The magnitude of unloading velocity and initial stress mainly influence strength and amount of sub-cracks on fissured rocks，but little on the law of expanding mode and deformation. The propagation of cracks is made by tensile stress brought via different rebound deformations and shear stress increasing but resisting shear decreasing under unloading；and the influence of these stresses on the expanding evolvement is highly related with dip angle of cracks.
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Received: 10 August 2009
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