Abstract: Due to the influence of fluctuation of reservoir water level, the joint surface of rock slope is affected by dry-wet cycles. The shear strength of joint surface after dry-wet cycles becomes one of the key factors to control the stability of rock slope. At present, the research on the shear damage constitutive of rock joint surface after dry-wet cycles is not sufficient. Taking the red sandstone in the Three Gorges Reservoir area as an example, we obtain the strength and deformation characteristics of red sandstone under dry-wet cycles by carrying out joint direct shear tests of red sandstone under different dry-wet cycle numbers, and give a modified Iwan joint surface shear damage constitutive model considering the effect of dry-wet cycles. The results show that the shear stress-displacement curve of the joint specimen is characterized by five stages: initial compaction, linear elastic deformation, pre-peak softening, post-peak failure and residual deformation. By introducing the Logistic model, the shear damage constitutive model of the joint surface can reflect the actual damage process of the joint surface and better describe the shear deformation behavior of the regular serrated joint surface in the compaction stage. There is a logarithmic relationship between the number of dry-wet cycles and the parameters of the modified Iwan shear damage constitutive model. Through laboratory tests, the accuracy of the modified Iwan joint surface shear damage constitutive model considering the effect of dry-wet cycles is verified. The model can effectively predict the relationship between shear stress and shear displacement of joint surface after dry-wet cycles. The research results can provide some reference for the study of shear slip failure mechanism and disaster prevention of rock slopes in the Three Gorges Reservoir area.

Key words: red sandstone, joint surface, dry-wet cycles, shear constitutive model