  In this article we formulate and implement a computational multiphase
periporomechanics model for unguided fracturing in unsaturated porous media.
The same governing equation for the solid phase applies on and off cracks.
Crack formation in this framework is autonomous, requiring no prior estimates
of crack topology. As a new contribution, an energy-based criterion for
arbitrary crack formation is formulated using the peridynamic effective force
state for unsaturated porous media. Unsaturated fluid flow in the fracture
space is modeled in a simplified way in line with the nonlocal formulation of
unsaturated fluid flow in bulk. The formulated unsaturated fracturing
periporomechanics is numerically implemented through a fractional step
algorithm in time and a two-phase mixed meshless method in space. The two-stage
operator split converts the coupled periporomechanics problem into an undrained
deformation and fracture problem and an unsaturated fluid flow in the deformed
skeleton configuration. Numerical simulations of in-plane open and shear
cracking are conducted to validate the accuracy and robustness of the
fracturing unsaturated periporomechanics model. Then numerical examples of wing
cracking and non-planar cracking in unsaturated soil specimens are presented to
demonstrate the efficacy of the proposed multiphase periporomechanics model for
unguided cracking in unsaturated porous media.
