## 4 Discussion
Hydrogen bonds readily form between these planes, leading to strong interlayer attraction and tight crystal layer connections. However, for kaolinite, water mainly adsorbs onto the  
Figure 13: Schematic diagram of intercrystallite structure changes in chlorite and kaolinite: (**a**) dry state; (**b**) submerged for 14 days; (**c**) submerged for 30 days; (**d**) submerged for 60 days. surface of the mineral, with little effect on interlayer spacing due to its small interlayer distance [44]. In contrast, chlorite exhibits more noticeable swelling upon contact with water. This swelling is partly due to the thickening of the bound water film at the particle surfaces, which increases the intergranular spacing and causes slight intergranular expansion (as observed by the changes in the sizes of chlorite and kaolinite unit cells in Figure 13a-d). Although the expansion is limited compared to more expansive minerals like montmorillonite, this mechanism plays a more significant role in chlorite compared to kaolinite [45; 46]. The expansion stress generated can be significant enough to compress and displace the quartz framework, leading to new intergranular cracks [47]. Under external loads, the quartz framework deforms, compressing the pore space. If the pore space becomes less than the volume of free water within the pores, the incompressible water exerts pressure, resulting in the expansion of other micropores. This leads to the formation of interconnected cracks within the clay minerals. Moreover, if the crack tips adsorb free water, the high curvature at these crack tips indicates the difference in the properties of adsorbed water from the water adsorbed on the pore walls, significantly reducing the fracture energy of the rock and lowering the critical stress necessary for crack initiation [48]. This explains the decrease in the elastic modulus of the rock samples. (4) Failure modes based on microscopic mechanisms: According to relevant standards and the experimental results, it can be inferred that clay minerals are relatively uniformly distributed within the quartz framework, as shown in Figure 14a. With increasing soaking time of sandstone, the clay minerals gradually expand. The analyses in (1), (2), and (3) above reveal increasingly irregular expansion, as shown in Figure 14b-d. Additionally, the area of cracks traversing the clay minerals gradually increases, leading to the formation of different failure states. Therefore, the failure modes through microscopic mechanisms offer a strong foundation for the mechanistic analysis presented above. Although this study primarily focuses on the effect of water immersion on rock weakening, it is important to acknowledge that, in real-world conditions, water and mechanical load often act simultaneously on rocks. This synergistic effect could lead to more complex degradation mechanisms than those observed in this study. Future research should investigate the combined effect of water and mechanical load on rock failure, as these factors can interact to accelerate the weakening process [49; 50]. Experiments simulating the combined effects of water immersion and mechanical loading will provide a  
Figure 14: Schematic diagram of failure mode evolution based on microscopic mechanisms: (**a**) dry state; (**b**) submerged for 14 days; (**c**) submerged for 30 days; (**d**) submerged for 60 days. more comprehensive understanding of rock behavior, especially in natural environments such as landslides, mining operations, and deep geological processes [8; 51]. Exploring these coupled effects will be crucial for more accurately predicting rock stability under real-world conditions.