ABSTRACT
In the previous Chapters, we have explored the nature of rock failure in uniaxial tension and uniaxial compression. However, we also have to consider the mechanisms of rock failure when a sample is subjected to more complex stress states. Experimental evidence indicates that rocks are significantly strengthened by confinement and that there is a brittle-ductile transition zone as the confining pressure is increased, i.e., beyond this zone the complete stress-strain curve continues to ascend, rather than descending as we have discussed for the uniaxial loading case in the previous Chapter. The behaviour of rock under the confinement condition is of fundamental and practical significance in both the structural geology and engineering fields. However, despite many years of theoretical and practical research, we still do not have a universally accepted failure criterion for the general case of a stressed rock sample, see Yu et al. (2009) where the main developments leading to a unified strength theory for geomaterials are described. Hence, the exploration of rock failure via numerical models continues to be helpful, as we will describe in this Chapter.
