Measurement of the fracture toughness K1C of rock was carried out through the evaluation of crack growth using calibration equations. Any point within the calibration range in the post-peak stage can be used to measure K1C. The AE monitoring revealed that large fracture processes started only when the load was near the peak of every cycle. AE bursts with large amplitudes increased with an increase in the crack growth.


La mesure du facteur d'intensite de contrainte critique K1C d'une roche a ete realisee en eValuant la croissance de fissure, grace aux equations de calibrage. Tout point de l'intervalle de calibrage, appartenant au stade post-pic, peut être utilise pour mesurer K1C. L'enregistrement de l'emission acoustique a revele que les procedes de large fracturation ne commençaient que lorsque la charge avoisinait le pic de chaque cycle. Les emissions acoustiques de grande amplitude augmentent avec la croissance de fissure.


Die Messung der Bruchzahigkeit K1C von Gestein wurde durch Berechnung des Bruchwachstums unter Anwendung der Kalibrierungsgleichungen durchgefuehrt. Jeder Punkt im Kalibrierungsbereich, der in der Phase nach dem Spitzenwert liegt, kann zur Messung Von Kic verwendet werden. Die Beobachtung der Schallemissionen zeigt, dass grosse Bruchprozesse nur beginnen, wenn die Belastung nahe an ihrem Spitzenwert in jedem. Zyklus liegt. Shallemissionen werden mit grossen Amplituden ausgesendet und nehmen mit Anstieg des Risswachstums zu.


Many stability problems in rock engineering are associated with fracture of rock. The resistance rock to crack growth is expressed by a term, the plane strain fracture toughness K1C, which is taken as a material parameter in fracture mechanics. It has been used in dealing with engineering problems in relation to fracture, such as hydraulic fracturing (Rummel and Winter 1982), gas driven fracturing (Nilson et Al.1985), tunnel boring (Lindqvist 1982), blasting (Rustan et al. 1983) and modelling of rock deformation (Nemat-Nasser and Obata 1988; Li and Nordlund 1993a and 1993b). The methods for determining the fracture toughness of rock are developed based on the analysis of well defined cracks. Ouchterlony (1986, 1988) and Sun and Ouchterlony (1986) have made great contributions in developing the test methods that have been accepted as the ISRM suggested methods. The chevron bending core specimen is one of the two specimens in the suggested methods. The main advantages of using this type of specimen are that the specimen preparation is easily carried out, the precracking is not needed, and the fracture is propagated within the slot. Loading cycles have to be performed in order to locate the critical point at which the fracture toughness is evaluated. In most of the cases, especially when the specimen is small, the nonlinearity correction has to be carried out in order to obtain an acceptable value for the fracture toughness. The stress field at a loaded crack tip is expressed by the stress intensity factor K that is related to the available energy release rate.


There exists a relation between the crack growth and the compliance of a bending beam, which can be established by experimental calibrations (Li and Wai 1990). Let g represent the dimensionless compliance of the bending beam, which is expressed by g=ED/S, where E is Young's modulus, D the diameter of the specimen and S the slope of the load vs. displacement curve. The initial and the growing crack lengths are represented by the dimensionless terms αο and α, which are defined as the ratios of the crack lengths to the diameter of specimen.

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