## 1 Introduction  
In addition to the Three Gorges Project, the reservoir area of large-scale hydropower projects in China often has a narrow and deep canyon field environment. The typical characteristics of high dams and large reservoirs and the large-scale water level drop caused by flood discharge can easily induce hydraulic erosion, seepage, latent erosion, dry-wet cycles, and other thorny problems in the reservoir fluctuation area that affect the stability of unloading rock mass after excavation of reservoir slopes [1]. On the one hand, the compound environment formed by high dams, large reservoirs, and narrow deep canyons provides a prerequisite for the excavation unloading rock mass in the water-fluctuation zone to fully soak and withstand high seepage pressure during the gradual impoundment of the reservoir. On the other hand, due to the comprehensive consideration of the maintenance of power stations, flood control of the reservoir and the prevention of infiltration damage of the slope, the large-scale sudden drop of water level forces the excavated reservoir slope of reservoir water-fluctuation zone to bear a sharp dry-wet cycle, which aggravates the structural deterioration of unloaded rock mass. Generally speaking, the open pores and cracks of the excavation unloading rock mass of the reservoir slope can be saturated under the impoundment, but the reservoir water drainage process cannot achieve its complete drainage. Under the induction of sunlight on the slope surface and the thermal conductivity of the rock mass, the deterioration of the pore structure of the rock mass induced by dry-wet cycle is bound to be more prominent in the reservoir slope of the reservoir fluctuation zone. Furthermore, the study of the dry-wet cycle of unloaded rock mass in reservoir slopes is of practical significance for comprehensively exploring the macro-meso-structure evolution mechanism of excavated rock mass on reservoir slopes in water-fluctuation zones. Excavation unloading exists widely in various kinds of geotechnical engineering construction; [PERSON] and [PERSON] [2] first began to study unloading rock mass mechanics in China, then many scholars at home and abroad also conducted in-depth research on unloading rock mass mechanics. Most of them start from the triaxial unloading test to study the crack evolution and failure mechanism, mechanical parameter damage degradation effect, and strength characteristics of various rocks during unloading [3; 4; 5; 6]. Considering the influence of unloading rate on rock failure mode, triaxial unloading tests under different unloading rates were designed and carried out to analyze the failure characteristics of rock [7; 8; 9; 10]. On this basis, many scholars intervened in the influence of various unloading paths and studied the energy evolution characteristics of rock in triaxial unloading failure processes from macro and meso perspectives [11; 12; 13]. With the gradual enrichment of test methods, many achievements have been made on the influence of dry-wet cycles on rocks from a microscopic point of view. [PERSON] et al. [14] and [PERSON] et al. [15] established the relationship between structural characteristics, fracture development trend, fractal dimension, and correlation dimension by analyzing the crack growth and acoustic emission characteristics of samples and studied the water weakening effect of dry-wet cycling on rocks. Based on the scanning electron microscope (SEM) test, [PERSON] et al. [16] proposed the concept of erosion degree of argillaceous sandstone under dry-wet cycles based on the analysis of mesoscopic images of rock samples with different dry-wet cycles and established the relationship between mesoscopic and macroscopic. On this basis, [PERSON] et al. [17] and [PERSON] et al. [18] established the meso-damage evolution equation based on fractal dimensions and studied the influence of dry-wet cycles on meso-characteristics of altered granite.