• Cracks at the slope crest tend to propagate in shear mode with an initiation angle of approximately 8°, while toe cracks may propagate in either tensile or shear mode.
• Shear crack initiation angle at the crest increases with slope angle, crack position parameter, and crack length parameter, but decreases with crack inclination angle, with a maximum variation of about 30°.
• Tensile crack initiation angle at the toe decreases with slope angle, crack inclination angle, and crack length parameter, while the influence of crack position parameter is minor, with maximum changes ranging from 25° to 60°.
• Theoretical predictions of crack propagation modes and directions align well with transparent soil model test results, validating the analytical stress field formula.