Effects of in-situ stresses on dynamic rock responses under blast loading

The depletion of shallow-buried reserves has been driving the exploitation activities into the deeper crust, and the rising lithostatic stress thus poses substantial challenges to dynamic rock breakage. In this paper, we present new mechanistic insights into the effects of in-situ stresses on blast responses of intact rocks via integrated analytical and numerical analyses. An elastodynamic framework was first developed to characterize the blast wave propagation in pre-stressed rocks. The analytical solution suggests that the rock pressure can essentially promote dynamic compaction by diverting the explosive loading path and suppress fracturing by imposing circumferential compression. Such effects are more pronounced in the minor principal stress (sigma(3)) direction of anisotropic stress fields. The rock responses under the coupled static-dynamic loadings were then simulated using a constitutive framework that was proven valid in this study for broad spectrums of pressures and strain rates. Image processing of the breakage patterns shows that the crushed zone contracts as the rock pressure rises. The crushed zone becomes elliptic in anisotropic stress fields, and its major axis coincides with the major principal stress (sigma(1)) direction and declines more slowly than the minor axis aligned with sigma(3). The orientation distribution shows quantitatively that fractures get increasingly more clustered around sigma(1) as stress anisotropy rises, and the fracture density decreases more rapidly in equibiaxial conditions with greater vertical stresses. The consistent insights of the analytical and numerical studies can improve the mechanistic understanding of the evolution of dynamic rock behavior in different in-situ stress conditions.