• Unconfined compression tests on unsaturated completely weathered granite reveal diverse stress-strain behaviors (brittleness, softening, ductility) controlled by moisture content and dry density.
• Unconfined compressive strength increases to an optimum at ~10.5% moisture content, then declines sharply beyond a critical value of 13.0%.
• Shear failure dominates the deformation and fracture of CWG specimens, with ultimate failure modes governed primarily by moisture content rather than dry density.
• A novel damage-based constitutive model accurately replicates the undrained mechanical behavior and quantitatively captures key mechanical indexes.