In practical engineering

the rock mass in the hydro-fluctuation zone of the bank slope is not only subjected to wet-dry cycles

but also influenced by overlying stress

especially clastic rocks represented by mudstone. To study the shear mechanical deterioration characteristics of mudstone in the hydro-fluctuation zone under the combined action of stress and dry-wet cycles

typical mudstone from the bank fluctuation zone of the Three Gorges Reservoir Area was selected as the focal point of this study

and water-rock interaction tests considering the combined action of overlying stress and dry-wet cycles were carried out. The findings revealed: (1) During the combined action of stress and dry-wet cycles

the overlying stress accelerated the deterioration of the shear mechanical properties of mudstone. The greater the overlying stress

the more obvious the decline of the shear stress-shear displacement curve and the steeper the decrease in its slope

and the lower the shear strength and residual strength. (2) The shear strength of mudstone demonstrated a degradation pattern characterized by an initial rapid decline

followed by a gradual slowdown

and ultimately stabilization. The degradation observed in the first five cycles accounted for over 70% of the total degradation

and within the same cycle period

higher overlying stress levels corresponded to greater degradation amplitudes. (3) The increase in overlying stress significantly deteriorated the mesoscopic structure of mudstone

promoting fracture expansion

increasing the contact area of water-rock interaction

and accelerating processes such as the dissolution of calcareous cement and the expansion and contraction of illite and montmorillonite

leading to increased porosity and loose structure of mudstone. The research outcomes offer valuable insights for assessing the stability of clastic rock bank slopes in the Three Gorges Reservoir area.