# A Review of the Evolution Characteristics and Argillization of Clay Interbeds in Rockslides
## 3 Parameter Changes during the Argillization Process
### Macroscopic Mechanical Properties  
Most of the clay interbeds originated from weak interlayers. After argillization, the mechanical and engineering properties of weak interlayers would significantly deteriorate. During argillization, the deterioration of mechanical properties can be influenced by other physical property parameters in a mutually dependent manner. The certain relationship among the physical property parameters should be established in terms of the overall study. There are numerous related parameters that require an index to represent them synthetically. The natural property index was adopted to include water content, compactness, storage environment, composition and content of clay minerals, consistency state, and comprehensive evaluation of strength [23]. And through the natural property index, correlation equations were established between particle size composition and shear strength parameters under various consistency conditions. The friction coefficient decreased rapidly with an increase in clay content. When the clay content exceeded 30%, the friction coefficient decreased gradually as the clay content increased, eventually reaching a stable state. Figure 5: The relationship between the number of cycles and disintegration rate of soil under different conditions (modified from [PERSON], [PERSON] [22]). Clay interbeds in different places have different critical water content. And the critical water content would also change with different stages of clay interbed formation [24; 25]. The moisture content of clay interbeds directly affects their macroscopic mechanical properties. With the increase in water content, the cohesive force increased first, then decreased after reaching the critical water content value. And when the water content exceeded 19%, the stress-shear displacement curve of the clay interbed would change from an obvious gradient to a gentle gradient. The angle of internal friction decreases with an increase in water content in red sandstone interlayers. The cohesive force increased first and then decreased with the change in water content [26; 27]. If the water content suddenly increases sharply due to continuous rainstorms, the ongoing process of argillization would further decrease the shear strength [28]. When the clay content is low and the coarse particle content is high, the shear strength will still be high. This is because the coarse particles play a skeleton role when subjected to shear. Moreover, the coarse particles would be uniformly distributed in the matrix if the clay content were high. The particles were separated by the clay filling, and the main slip under shear would occur at the clay layer, which facilitated directional arrangement. As a result, a low shear strength was obtained. Therefore, the dynamic response characteristics of a bedding rock slope will be affected to a certain extent by the particle content. The grain size distribution trend, relief degree, and thickness will also influence the shear strength of clay interbeds [29; 30]. When the relief degree of the slip surface exceeded the thickness of the clay interbed, it resulted in a higher shear strength due to the slip-up effect caused by the change in contact mode. The dynamic strength index of clay interbeds is much higher than the static strength index [31]. Based on the clay interbed found in the left bank of the Xiaolangdi hydropower project of the Yellow River, the suggested value of the total dynamic strength index was obtained. The temperature will affect the shear strength after a critical degree, although the normal temperature did not play a strong controlling role in the formation of clay interbed. If the temperature exceeded 800 degrees, sandstone would completely change from shear failure or tensile failure to total collapse. But before 800 degrees, the shear strength of sandstone only fluctuated slightly [32].