Recent laboratory studies of the flow and fracture of rocks under general triaxial compression are reviewed .New Developments in laboratory techniques have made it possible to measure three principal stresses and strains under general triaxial stress states

in which all three principal stresses are different . Strength and ductility of isotropic rocks are markedly affected not only by the least compression σ3

although these two effects are rather additional in strength

but opposite in ductility .The experimental results show that dilatancy is highly anisotropic rocks have been also measured under the general triaxial compression .In this case

the effect of the intermediate compression markedly depends on the orientations of the weak planes.