Multiscale analyses of failure pattern transition in high-porosity sandstones

High-porosity sandstones are important host rocks for hydrocarbon and groundwater reservoirs. It is of significance to investigate their failure pattern transitions under different loading conditions. A hierarchical multiscale modeling approach is employed, coupling the finite element method and the discrete element method, to compare and analyze the failure pattern transition in typical geotechnical boundary value problems, e.g., (drained) biaxial compression tests, borehole stability problems, hydro-mechanical problems, etc. The failure patterns with distinct geometric features, including pure compaction band and shear-involved deformation band, are formed under different loading conditions. The transitions between different patterns, due to stress concentration, boundary conditions, pore pressure, etc., complicate the failure patterns in boundary value problems. The increase in the effective mean stress tends to transit the shear-involved band deformation to the compaction band one and the decrease tends to cause the transition from the compaction band deformation to the shear-involved band one.