## 4 Analysis of Data Sources and Evaluation Factor Selection
### Analysis of Evaluation Factor Selection
#### 4.2.6 Engineering Geological Rock Formations  
The lithology of the strata provides the structural foundation for landslides, and various engineering geological rock formations have unique mechanical and physical characteristics that lead to various kinds of disasters. The soil body that constitutes a slope is not only subject to gravity, but also to shear stress, and the geotechnical soil that resists the effective stress determines both the likelihood of the occurrence of slope failure and the change in slope instability in time and the nature of the geotechnical body is of considerable importance to both the occurrence and the development of slope failure. The mechanical properties of the geotechnical body depend on the particle and mineral composition of the geotechnical body, the structural configuration of the geotechnical body, the nature of adsorbed cations and the nature of pore water, and the composition and structure of the geotechnical body depend on the cause of the geotechnical body and the historical processes it has undergone. The study area's stratigraphic lithology is separated into seven categories of engineering geological rock formations, such as loess-like subsandy soil monolayer soil and interbedded, relatively weak sandstone conglomerate (Figure 9). The engineering geological rock formations in the study area with the most developed disasters were discovered to be the tougher layered volcanic clastic rock formations and the weakly interlayered sandstone conglomerate.  
The middle mountainous area and the pile hilly area, with a slower topography, are important loess distribution areas, and loess landforms such as loess beams can often be seen. The structure of the soil is relatively dense, and slightly wet, with small wormholes containing calcareous nodules and conchoidal shells, and columnar joints are developed.  
Figure 9: Tekes County engineering geological rock formation. A—An interbedded hard to weak clastic rock group that is primarily made up of sandstone and mudstone; B—A hard intrusive rock formation; C—A relatively hard–medium thick-layered carbonate rock formation; D—A multiple-layer system of sand, gravel, and silt; E—A layered weak clastic rock formation that is dominated by mudstone; F—A single-layer soil that contains pebbles and gravel; G—A block, hard- to weak-layered clastic rock formation that is dominated by sandstone.  
From the results of the particle analysis of the soil, it can be seen that they are all powdery clay and clay, and in the east-west direction, there is a trend of the powder content increasing from west to east. The loess-like soil monolayer is the most widely covered geotechnical body in the landslide-prone area, and its lithology is light yellow-greyish-yellow chalk. Its structure is relatively loose, wormholes, large void structures, and vertical joints are relatively developed, and the shear strength is relatively high in the unsaturated state, but greatly reduced when saturated with water. Its main physico-mechanical indexes are as follows: natural water content (\(\omega\)) in 8.14\(\sim\)21.3%, specific gravity (Gs) in 2.70\(\sim\)2.71, porosity (n) in 0.42\(\sim\)0.54, plasticity index (IP) in 7.68-13.23, compression coefficient (\(\mathrm{a_{V}}\)) in 0.89 MPa\({}^{-1}\)-1.06 MPa\({}^{-1}\), compression modulus (Es) in 2.05-2.42 MPa, high shear strength in the natural state, cohesion (c) in the range of 9.13-48.3 kPa, and angle of internal friction (\(\varphi\)) in the range of 13-37\({}^{\circ}\), and the strength decreases rapidly after contact with water, with the cohesion (c) in the range of 3.7\(\sim\)20.1 kPa, and the angle of internal friction (\(\varphi\)) in the range of 11-33\({}^{\circ}\).