###### Abstract  
The effect of the dry-wet cycle, characterized by periodic water level changes in the Three Gorges Reservoir, will severely degrade the bearing performance of rock formations. In order to explore the effect of the dry-wet cycle on the mesoscopic damage mechanism of jointed sandstone, a list of meso-experiments was carried out on sandstone subjected to dry-wet cycles. The pore structure, throat features and mesoscopic damage evolution of jointed sandstone with the action of the dry-wet cycle were analyzed using a-low-field nuclear magnetic resonance (NMR) technique. Subsequently, the impact on the mineral content of dry-wet cycles was studied by small angle X-ray scattering (SAXS). Based on this, the mesoscopic damage mechanism of sandstone subjected to dry-wet cycles was revealed. The results show that the effects of the drying-wetting cycle can promote the development of porous channels within sandstone, resulting in cumulative damage. Besides, with an increase in dry-wet cycles, the proportion of small pores and pore throats decreased, while the proportion of medium and large pores and pore throats increased. The combined effects of extrusion crush, tensile fracture, chemical reaction and dissolution of minerals inside the jointed sandstone contributed to the development of mesoscopic pores, resulting in the increase of porosity and permeability of rock samples under the dry-wet cycles. The results provide an important reference value for the stability evaluation of rock mass engineering under long-term dry-wet alternation. dry-wet cycle; jointed sandstone; mesostructure; porosity; damage characteristics +
Footnote †: journal: Applied sciences  
0000-0002-4307-2278-2  
number of dry-wet alternating cycles. [PERSON] et al. [16] investigated the evolution mechanisms of sandstone damage under the action of alternating dry-wet cycles. It was found that the strength of the rock gradually decreased under this action. [PERSON] et al. [17] discussed the influence of dry-wet alternation action on the physico-mechanical parameters of sandstone, and found that the elastic modulus and density decreased with the increase of the number of dry-wet alternating cycles. [PERSON] et al. [18] revealed the relationship between the degradation mechanism and dry-wet alternation. [PERSON] et al. [19] studied the mechanical properties of sandstone and declared that the tensile strength and compressive strength decrease with the increase of the wet-dry alternation number, while [PERSON] et al. [20] found that the degradation of surrounding rocks was accelerated by long-term water circulation. [PERSON] et al. [21] researched the mechanical stability of sandstone under acidic dry-wet cycles and dynamic loading, and noted that peak stress and elasticity decreased as the acidity and cycle frequency increased. In the research mentioned above, the macroscopic damage features and evolution laws of rock masses subjected to dry-wet alternation is revealed. However, research on the internal damage of jointed rock masses during dry-wet alternation action is relatively scarce. Rock masses are a complex solid material, and it is hard to accurately measure or describe their meso-damage by means of the conventional methods. In recent years, nuclear magnetic resonance technology (NMR), CT scanning technology and other technical methods have been widely adopted to research the meso-degradation law of rock [22; 23; 24; 25]. With the aid of CT scanning technology, [PERSON] et al. [26] explored the cracking process in coal and rock under compression and found that the cracking process is partitioned into an initial stage, a stable growth stage and an accelerated growth stage. [PERSON] et al. [27] studied the mesoscopic damage of fractured sandstone under compression, and proposed a macro-meso damage constitutive model using logistic growth theory. [PERSON] et al. [28] concluded that cohesion and internal friction angle decrease under the action of dry-wet alternation. [PERSON] et al.