Study of Rock Fracture by Permeability Method

The permeability of sandstone was measured in triaxial tests. Within the range of confining pressures used here, permeability as a function of differential stress was found to decrease until a minimum value was reached at about 60–70% of the fracture strength, i.e., at a stress that lies between the crack-initiation stress and the stress corresponding to the volumetric strain reversal. Thereafter, permeability started to rise, and at about 85–90% of the fracture strength its rate of increase was greater. The permeability method was not sensitive enough to mark the point of crack initiation and the onset of crack coalescence. However, differential stress versus volumetric strain curves were, in general, similar to differential stress versus permeability curves. Thus, the permeability method can be successfully used to study the fracture mechanism of rocks.