# A Review of the Evolution Characteristics and Argillization of Clay Interbeds in Rockslides
## 2 Definition and Formation of Clay Interbed
### Formation Stage of Clay Interbeds  
The formation of clay interbeds is the combined effect of macro and micro changes. The change in macro-structure is beneficial for the change in micro-structure. The localized non-uniform stress caused by microscopic changes exacerbates the failure of the macrostructure.  
Based on the assessment of structural damage, the argillization and disintegration of soft rock strata need to go through three processes: (1) failure process in the macrostructure; (2) loss of water in soft rock; and (3) the physicochemical process of clay mineralization produced via water absorption of damaged rock mass [11]. This stage division highlighted that the argillization process was a gradual transition from macroscopic disturbance to microscopic destruction, and it could be further divided into: (1) relatively calm lacustrine sediments being deposited and undergoing diagenesis; (2) undergoing intense tectonic activity; (3) physical weathering of rock masses due to changes in environmental conditions and the influence of tectonism; (4) weathering further causing water to penetrate into the rock mass, resulting in chemical weathering that generates various clay minerals; and (5) the function of clay minerals in terms of repeated flocculation and dispersion due to changes in the electric layer. It continuously breaks the particle, and the argillization process continues to occur [12].  
The formation stages from the weak interlayer to the clay interbed were further divided based on relevant laboratory experiments [13]: the sedimentary stage of soft rock, tectonic shear stage (interbed of shear fracture zone), groundwater hydrochemical stage (shear fracture zone with clay), and formation stage of clay interbed. This classification only expressed the main behavior in the process of the stage, and there were some differences between laboratory and in-site experiments. The argillization rate is very slow in the laboratory tests, and it could not be completely consistent with the actual conditions of inflow and loss of water.  
The evolution process could be divided into the ion exchange adsorption stage, mineral dissolution stage, and softening and disintegration stage according to the chemical elements. It was closer to the actual situation. The groundwater action was regarded to be the main influence in the whole evolution process [14]. Clay mineralization occurs not only in the final stage but also at different rates in each stage.  
Figure 2: Formation of clay interbed.  
According to the grain size composition and thickness of the clay interbed, it can be divided into five types: (1) clay, (2) clay with breccia, (3) clay with silty sand or silty sand with clay, (4) clay membrane, and (5) breccia with clay [9].  
The formation stages of clay interbeds have been discussed, including structure damage, laboratory experiments, chemical elements, and grain size. These views are mutually supportive and complementary to one another. But it still lacks a more uniform criterion for classification without considering the parent rocks, structural types, and mineral compositions of numerous clay interbeds as a basis.