Damage evolution and propagation paths of en-echelon cracks

A continuum damage mechanics model simulates the stress and damage fields and the corresponding paths of pressurized en-echelon cracks. The model includes gradual strength degradation and subcritical crack growth, together with development of process zones, strain localization and brittle failure. Prior to onset of damage, the calculated stress field around the pressurized cracks is the same as that produced by linear-elastic models. After the onset of damage, localized damage zones spread out around the crack planes, and their shape is sensitive to the state of stress. The model reproduces shapes of damage lobes and geometries of crack connections that are commonly observed around en-echelon dyke segments in sandstone. Thus, the distributed damage and the crack paths may help to better estimate the state of stress acting during growth of pressurized cracks (dykes). The close kinship between dykes and artificial hydrofracturing provides an economic incentive to incorporate our results in hydraulic fracturing analyses.