• A novel damage variable equation integrating acoustic emission and resistivity parameters accurately characterizes damage evolution in sandstone under cyclic loading.
• The derived damage constitutive equation closely matches experimental data, validating its predictive capability for rock behavior under varying water contents.
• Nondestructive monitoring techniques (AE and resistivity) prove effective for real-time assessment of rock damage, offering advantages over destructive methods.
• The findings provide a theoretical foundation for enhancing safety and stability monitoring in underground rock engineering, particularly in water-sensitive conditions.