## 4 Macro and Micro Damage Analysis  
### Macro and Micro Analysis of the Influence of Water-Shale-Rock Interaction on the Strength of Shale  
The effect of water on shale reflects a complex stress corrosion process, accompanied by the physical and mechanical behaviors of clay, such as slime expansion, water absorption, and disintegration. The main forms of water molecules in shale are as follows: (1) interlayer-bound water; (2) binding water between clay particles; (3) free water between pores and cracks. Among them, surface adsorption is the main process of cell-water interaction. The surface adsorption of water molecules reduces the surface energy of the cell, resulting in the expansion of the cell structure. During the interaction between water molecules and crystal cells, the energy, bonding morphology, and ion distribution characteristics of the crystal cells will change greatly. When water molecules enter the interlayer, the van der Waals force decreases, most notably in the cell energy system, and the interlayer binding water molecules deteriorate the interlayer bonding force. The bonding force between the mineral components of the shale is mainly produced by the clay minerals content when the shale rock is under water; on the one hand, the clay minerals content forms a hydration film that adsorbs water molecules, and the original clay cement forms a water-binder link. This causes the bonding forces and friction between the particles to weaken, and the water molecules act to lubricate. On the other hand, the clay particles become negatively charged, and the cations in the aqueous solution are enriched on the surfaces of the clay particles to produce osmotic repulsion. This causes the distance between the clay particles to become larger, and the water molecules act to wedge. According to the theory of the diffusion of a double layer of water-saturated clay particles in soil mechanics, the bonding force of clay is a manifestation of the attraction and repulsion between particles under the action of water and shale rock. With the increase in water content, the interaction force between particles decreases, and the shale rock cementation strength and micromechanical parameters deteriorate in water. Therefore, the fracture toughness of water-containing shale rock samples is lower than that under dry conditions. With the increase in water content, the primary cracking speed in shale becomes faster; thus, the strength of the shale rock sample with a higher water content will be lower. This is consistent with the experimental results. The effects of water on the macroscopic strength of the shale main rock are reflected in the following: (1) water absorption expansion; (2) cementing or disintegration; (3) solution/subduction; (4) pore pressure; (4) seepage dragging force; (6) deterioration of strength. The water-absorbing expansion of clay mineral particles and the water-absorbing expansion of clay mineral crystal cells are the intrinsic characteristics of the water-absorbing expansion of shale. When clay minerals encounter water, a hydration film is formed between particles. As water molecules are continuously embedded into clay particles, the gap between clay mineral particles increases, the microstructure is damaged, and the bonding force decreases. Macroscopically, the clay cement is argillated to form a fine slime. When the pore water shows fluidity under external loading, the small particles of pelletized clay are carried away, showing the phenomenon of latent erosion. In terms of mechanical properties, when the shale rock encounters cement, the internal argillaceous connection weakens to a hydrocolloidal connection, and the cohesion and internal friction angle of shale rock decrease. During the process of subduction, the bonding force of shale rock de deteriorates, its strength decreases, and large deformation occurs.