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To study the deformation and failure mechanism of hard rocks, true triaxial compression tests were conducted on four types of hard rocks to obtain the complete stress-strain curves and failure modes. Under true triaxial compression conditions, the shapes of the complete stress-strain curves can be divided into three types: elastic-brittle (EB), elastic-plastic-brittle (EPB), and elastic-plastic-ductile (EPD) types. According to the different post-peak deformation behaviours, the stress-strain curves of EPB type can be subdivided into three sub-categories: post-peak instantaneous brittle (EPB-I), postpeak multi-stage brittle (EPB-M), and post-peak delayed brittle (EPB-D). The stress-strain curves change from EPD to EPB-D, EPB-M, EPB-I, and finally EB with increasing differential stress ([[sigma].sub.2] - [[sigma].sub.3]). The deformation characteristics are dependent on intermediate principal stress [[sigma].sub.2], minimum principal stress [[sigma].sub.3], mineral compositions, and mineral textures of rock samples. An increase in [[sigma].sub.3] leads to an increased ductility, while an increase in [[sigma].sub.2] leads to an increased brittleness. Moreover, rocks with regular mineral textures and low mineral hardness are more prone to ductility. When the deformation curve is transformed from EPD to EPB and then to EB, the tensile crack gradually predominates, and the macroscopic failure angle gradually becomes steeper. Key words: differential stress, mineral properties, tensile crack, deformation behaviour, failure modes. Afin d'etudier le mecanisme de deformation et de rupture des roches dures, de veritables essais de compression triaxiale ont ete realises sur quatre types de roches dures pour obtenir les courbes completes de contrainte-deformation et les modes de rupture. Dans des conditions de compression triaxiale reelle, les formes des courbes completes de contrainte-deformation peuvent etre divisees en trois types : elastique-fragile (EB), elastique-plastique-fracture (EPB) et elastique-plastique-ductile (EPD). En fonction des differents comportements de deformation post-crete, les courbes de contrainte-deformation du type EPB peuvent etre subdivisees en trois sous-categories : cassant instantane post-crete (EPB-I), cassant multi-etapes post-crete (EPB-M) et cassant retarde post-crete (EPB-D). Les courbes de contrainte-deformation changent de EPD a EPB-D, EPB-M, EPB-I, et finalement EB avec une contrainte differentielle croissante ([[sigma].sub.2] - [[sigma].sub.3]). Les caracteristiques de deformation dependent de la contrainte principale intermediate [[sigma].sub.2], de la contrainte principale minimum [[sigma].sub.3], des compositions minerales et des textures minerales des echantillons de roche. Une augmentation de [[sigma].sub.3] conduit a une ductilite accrue, tandis qu'une augmentation de [[sigma].sub.2] conduit a une fragilite accrue. De plus, les roches de texture minerale reguliere et de faible durete minerale sont plus sujettes a la ductilite. Lorsque la courbe de deformation est transformee d'EPD en EPB puis en EB, la fissure de traction predomine progressivement, et l'angle de rupture macroscopique devient progressivement plus prononce. [Traduit par la Redaction] Mots-cles: stress differentiel, proprietes minerales, fissure de traction, comportement de deformation, modes de defaillance., Introduction The stability of excavations in rock engineering (including deep tunnels and underground chambers) is of interest. As the depth of underground engineering operations gradually increases, rock masses are frequently [...]

To select an appropriate notch prefabrication method and notch length for obtaining relatively accurate and reliable rock mode I fracture toughness (KIC), as well as to improve understanding of macro fracture process and meso-fracture characteristics in the rock three-point bending test, three methods, i.e., wire cutting, saw blade cutting and water jet cutting were used to prefabricate notch in granite and marble specimens for three-point bending test. The comparison of micro fracture characteristics among three different cutting methods was conducted with the application of scanning electronic microscopic. The test results show that the effect of wire cutting method on KIC is the smallest. In addition, three-point bending tests on granite and marble containing dimensionless notch length of 0.1, 0.2, 0.3, 0.4, and 0.5 show that KIC tends to increase firstly and then decrease with increasing notch length. The dimensionless notch length of α = 0.3 is recommended for obtaining the representative KIC. The macroscopic failure of rock specimen undergoes a process of initiation of localization zone, development of localization zone, crack initiation, and finally fracture propagation. The acoustic emission process of rock specimen is observed with an obvious brittle characteristic, the crack opening displacement curve is consistent with the trend of cumulative acoustic emission curve, and the evolution of crack opening displacement curve can be regarded as a macroscopic characterization of the specimen internal failure development process.