# Analysis of Slope Stability in Ion-Adsorption Rare Earth Mine Under In Situ Leaching Condition
## 2 Methodology  
### Overview of the Studied Slope  
The studied ion-adsorption type rare earth mine is located at northwest of Cenxi, China. The terrain of the mining area consists of low mountains and hills, predominantly oriented in a northwest direction. Elevations range from 100 m to 300 m, with valleys typically between 85 m and 150 m. The slopes are relatively gentle, with gradients usually less than 40\({}^{\circ}\). These rare earth oxides are concentrated in the upper and middle sections of the granite-weathered crust, making the fully weathered layer the host for rare earth ore. The configuration of the ore body is heavily influenced by the terrain, undulating with the terrain, but to a lesser degree. The thickness of the ore body varies with its topographical position, and changes at the top, middle, and bottom of slope are stable: it is thickest in the middle of slopes with an average of 10.40 m, followed by the top slopes with an average of 10.06 m, and thinnest at the bottom with an average of 9.18 m. Generally, the central mining area, which is the initial mining area, shows a relatively greater average thickness. The ore bodies are positioned above the local erosion base level, and the terrain is conducive to natural drainage. No fault structures have been observed within the mining area. The hydrogeological boundary conditions are uncomplicated, with the ore bed resting on slightly weathered granite, which possesses strong water-blocking properties. The area has a well-developed surface water system characterized by rich vegetation and dense forest growth.  
The physical and mechanical properties of soil and rock are important parameters [30; 31] for calculating slope stability. Therefore, geotechnical exploration is essential to obtain the necessary parameters for verifying slope stability. Figure 2 presents photographs from the selected geotechnical exploration sites. Based on the test results of soil mass samples from the survey area and referencing relevant standard requirements along with comprehensive experience, recommended values for the physical and mechanical parameters of the slope's soil layers are provided in Table 1.  
Establishing the slope calculation profile is fundamental to building a geological model for slope stability analysis. A typical slope profile was selected through comparative analysis as illustrated in Figure 3. The chosen in situ leaching model of the rare earth mine in this study measures 76 m in width and has a maximum slope height of 41.6 m, with slope gradients ranging from 29\({}^{\circ}\) to 42\({}^{\circ}\). Field drilling identified four stratigraphic layers: topsoil, fully and semi-weathered granite zone, weathered layer, and bedrock.  
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multirow{3}{*}{**Soil Layer**} & \multirow{3}{*}{
\begin{tabular}{} \end{tabular} } & \multicolumn{4}{c}{**Shear Strength**} & \multicolumn{2}{c}{**Uniaxial**} & \multicolumn{2}{c}{**Design**} \\  & & & & & & **Strength of** & **Value of** & **Osmotic** \\  & & **Density** & & **Natural State** & & **Saturation State** & **Rock (MPa)** & **Bond** & **Coefficient** \\  & **(g/cm\({}^{3}\))** & **(g/cm\({}^{3}\))** & & **Cohesive Force C** & **Internal Friction Angle \(\psi^{\prime}\) (\({}^{\circ}\))** & **Cohesive Force C** & **Internal Friction Angle \(\psi^{\prime}\) (\({}^{\circ}\))** & **Saturation State** & **(firf)** & **(cm/s)** \\ \hline Topsoil Layer & 18.0 & 19.0 & 32 & 20 & 27 & 18 & / & 55 & \(8.2\times 10^{-3}\) \\ Completely & & & & & & & & & \\ Weathered & & & & & & & & & \\ Weathered & & & & & & & & & \\ Weathered & & & & & & & & & \\ Granite Zone & & & & & & & & & \\ Layer & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Recommended physical and mechanical parameters for various soil layers of the slope.  
Figure 2: (a) Partial borehole core and (b) in situ shear test.