Effect of the triaxial stress system on the failure of dolomite and limestone

Abstract

Failure under conditions of triaxial stress, in which two of the principal stresses are equal, have been studied intensely, but few investigations of the effect of the more general combined stress system have been made because of the experimental difficulties of achieving conditions of true homogeneous triaxial stress. A new triaxial apparatus has made possible the study of failure of brittle rocks under a general triaxial stress system in which all three principal stresses are different. By this method, the effects of the stress system to the fracture stress, yield stress and the ductility in several rocks. Dunham Dolomite and Solenhofen Limestone were experimentally studied. The fracture strength increases markedly not only with the increase of the least compression σ 3 but also with the increase of the intermediate compression σ 2, except for very high σ 2. The influences of σ 2 and σ 3 on the ductility and the stress drop, however, are just the opposite. A new empirical failure criterion, which corresponds to the modified von Mises theory, correlates the present results satisfactorily.