Mudstone is susceptible to disintegration and argillization when it encounters water. To reveal the evolution of deformation and damage characteristics of mudstone under water-rock interaction

this paper conducts dry-wet cycles experiments on mudstone specimens

collects speckle images of the whole process of experiments by binocular camera

and calculates the three-dimensional displacements and strains on the surface of specimens by using three-dimensional digital speckle correlation software MultiDIC. The results indicate that under dry and wet cycling conditions without externally applied anthropogenic forces

the uneven water absorption and water loss of the mudstone specimen leads to differential expansion and contraction deformation in the adjacent areas. The local tensile strain and shear strain increase significantly in the transition zone of expansion and contraction deformation

where the new crack occurs. The tensile deformation is perpendicular to the crack surface. The direction of shear displacement is along the potential crack surface but perpendicular to the direction of the specimen surface. The specimen shrinks in the center of the specimen when it loses water

while the surrounding area is still expanding due to water replenishment from the center of the specimen. The speed of water loss deformation slows down

but the duration of water loss is longer

and the total deformation is greater than that during the immersion period. As the number of dry-wet cycles increases

the growth rate of crack width and depth first increases

then decreases

and finally tends to be stable. The crack surface becomes a new free surface

with the redistribution of expansion and contraction zones.