In the paper is presented a new linear strength criterion with the assumption that (i) decisive about the brittle failure of rock material are both the shearing stresses and the normal tensile stresses, (ii) in a clastic material, the tensile stresses may be evoked also when the applied stresses are the compressive ones, (iii) the relation between the shearing stresses and normal tensile ones is expressed by a linear function. In the new strength criterion 61 - 6c + d 623,the coefficient d is a certain function of the so-called brittleness index of the rock z=6c/6T and a parameter depending on the rock structure v'. Taking as an example six different sandstones and granites, it has been shown that, contrary to Sondal- Botkin-Mirolubov criterion, Anderson criterion and modified Griffith criterion, the new linear' criterion expresses at least well the ultimate strength of these rocks in the conditions of conventional triaxial compression, approximating the empirical data 61=f(63-62) with the values of parameter v' equal to 0.41+0.45 for sandstones and 0.13+0.21 for granltes.
Dans cet article on a presente un critère nouveau de rupture fragile des roches en admettant que (i) ce sont des contraintes de cisaillement ainsi que des contraintes normales de traction qui decident de la rupture fragile des roches, (ii) qu'en materiau clastique des contraintes de traction peuvent apparaître aussi dans une situation où des contraintes appliquees ce sont des contraintes de compression, (iii) qu'on exprime la relation entre des contraintes des cisaillement et des contraintes normales de traction par la fonction lineaire. Dans le nouveau critère de rupture 61 - 6C + d 623 le coefficient d c'est une fonction de l'indice de fragilite z-6c/6T et du parametre v' dependant de la structure d'une roche. On a montre sur six exemples des grès et des granites differents qu'au contraire du critère de Sondal-Botkin-Mirolubov, du critère d'Anderson et du critère modifie de Griffith, ce nouveau critère lineaire exprime au moins bien la resistance ultime de ces roches dans les conditions de la compression triaxiale de revolution, en approximant des donnees empiriques 61-f(63-62) aux valeurs du paramètre v' egales 0,41+0,45 pour des grès et 0,13+0,21 pour des grànites.
Im Artikel ist ein neues lineares Bruchkriterium angegeben worden, unter der Voraussetzung, daβ (i) vom Sprödbruch des Gesteins sowohl Schubspannungen als auch normale Zugspannungen entscheiden, (ii) im klastischen Material können die Zugspannungen auch dann entstehen, wenn angelegte Spannungen Druckspannungen sind, (iii) der Zusammenhang zwischen Schubspannungen und Zugspannungen mit linearer Funktion ausgedrueckt ist. Unter neuem Bruchkriterium 61=6c + d 623 stellt der Koeffizient d eine Funktion des sogenannten Sprödigkeits wertes des Gesteins dar z-6c/6T und des vom Gefuege abhangigen Parameters V'. Am Beispiel von sechs unterschiedlichen Sandsteinen und Graniten ist gezeigt worden, daβ im Gegensatz zum Sondal-Botkin.Mirolubov-Kriterium, Anderson-Kriterium und modifiziertem Griffith-Kriterium, das neue Linearkriterium mindestens gut die Grenzfestigkeit dieser Gesteine bei triaxialer Beanspruchung auβert, approximativierend empirische Angaben von konventionellen dreiachsigen Druckversuchen 61-f(63-62) mit den Parameterwerten V' gleich 0,41+0,45 fuer Sandsteine und 0,13+0,21 fuer Granite.
The results of experimental and theoretical studies on the mechanism of brittle failure seem to indicate that in the case of the material subjected to a triaxial state of stress the damage of its structure is not only the result of shearing stress or only normal stress; it is both of these stresses that are always decisive about the process of fracturing.
The shearing stresses loosen the material and prepare the fracture, however, the breaking of continuity (and macroscopic failure) of the material occurs as a result of the normal tensile stresses.
Such stresses may be evoked not only in the material subjected to tension (this case was analyzed by Pisarenko and Lebedev, 1969, 1976), but also when the so-called applied stresses are the compressive ones.
And it is just this case of a material subjected to triaxial compression in which tensile stresses occur as a result of compression, that will be examined in this paper with the purpose of deriving the criterion of brittle failure expressing the ultimate strength of such a material in the function of confining pressure.
On the basis of an analysis of the mechanism of deformation of a certain clastic model made up of discs with a definite diameter (representing atoms, molecules or grains) and connecting springs with a definite stiffness (representing atomic interaction forces, intermolecular forces or intergranular bonds), Trollope, 1966, 1968 (cf. also Brown and Trollope, 1967) has shown that if 61, 62 and 63 are applied stresses acting in three mutually perpendicular directions, then the corresponding effective stresses are defined by the following formulae:
