The damage of mudded intercalation is an important factor affecting the slope stability.To study its damage mechanism

the compression tests under different confining pressures are carried out.The damage conditions are analyzed by the test data and the appearance of the failed specimens.CT scanning is used to carry out real-time CT scanning of the mudded intercalation at different loading times.Combined with MATLAB image processing

the damage recognition images of the mudded intercalation under different confining pressures are obtained

which reflect the development of the internal damage.Finally

according to the generalized strain equivalence principle

the damage variables are determined by the deformation modulus

and the relationship between the damage variables and the axial strain of the mudded intercalation is obtained.The results show that:（1）The strength of muddy intercalation generally increases with the increase of confining pressure

and the failure strain is 10%.Because of the difference of composition and structure

this strength rule is not obvious for certain samples;（2）There are weak layers in the muddy intercalation

and a small periodic collapse occurs during the loading process

showing a strain increase in the strength curve;（3）The damage and failure modes are different with and without confining pressures.Brittle failure is observed without confining pressures

and crack initiates and develops.Under certain confining pressures

plastic failure occurs

characterized by the compression of muddy intercalation

with the voids and fractures being closed.The critical confining pressure is between 0～50 kPa;（4）The damage equation established by this method fits well with the experimental results under different confining pressures

which is reasonable and feasible.