## 3 Experimental Results and Analysis
### Scanning Electron Microscopy Test and Analysis of Results
According to the theory of electric double layers, the electric double layer is formed by a fixed layer and a diffusion layer [15]. When heavy metals enter the soil, the chemical composition of the soil internally changes, the ionic balance is broken, the negative charge on the surface of the soil particles of heavy metal cations increases, the negative charge on the surface of the soil particles of heavy metal cations increases,, and the thickness of the electric double layer diffusion is affected. and the thickness of the electric double layer diffusion is affected. The attraction between soil particles weakens; that is, the distance between clay minerals increases with the increase in heavy metal ion concentration, proving that Guilin red clay is reshaped when heavy metal ions enter it. Due to the internal changes, the original ion balance inside the body of the soil breaks, decreasing the particle zeta potential. The thickness of the electric double layer diffusion and the attraction between soil particles decreased, and the distance between the soil particles increased. The result is similar to the role of lubrication under the same effect of normal stress. The friction between the particles weakened. 1. The results of the mercury pressure test indicated that the heavy metal (Pb\({}^{2+}\)) has a significant effect on destroying the microstructure of the soil. In addition, as the concentration of Pb\({}^{2+}\) increases, the pore space continuously expands, and the small pore space gradually becomes large pore space, thereby increasing the volume of the soil unit. The smaller the pore structure, the weaker the erosion effect. 2. The results of the electron microscope scanning test further illustrated the results of the mercury piezoelectric test. Under the influence of Pb\({}^{2+}\), an increase in the concentration of Pb\({}^{2+}\) reduces the thickness of the red clay's double electric layer, and the interparticle interaction force likewise becomes weaker as a result, producing a similar lubricating effect. 3. The results of the above two preceding experiments indicate that the microscopic mechanism of Pb\({}^{2+}\) contaminated Guilin red clay is as follows: on the one hand, when the heavy metal ions enter the soil body, the soil body generates fissures, which increases the pore volume and causes the structure to loosen; on the other hand, the thickness of the double electric layer on the surface of the soil particles decreases, which weakens the particle-particle interaction. In conclusion, the macroscopic mechanical properties of the Pb\({}^{2+}\) contaminated Guilin red clay are affected by two aspects. [PERSON], [PERSON] ([PERSON]), [PERSON] ([PERSON]), [PERSON], [PERSON] and [PERSON] conceived the presented ideas and elaborated the method. [PERSON], [PERSON] ([PERSON]) and [PERSON] wrote the manuscript. [PERSON]. ([PERSON]), [PERSON] ([PERSON]) and [PERSON] implemented the methods and performed the experiments. [PERSON] and [PERSON] supervised the research. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Heavy Metal Pollution Concentration** & 0\% & 0.1\% & 0.5\% & 1.0\% \\ \hline
**Porosity** & 56.82\% & 59.62\% & 62.97\% & 63.73\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Porosity of Pb\({}^{2+}\)-contaminated Guilin red clay. **Funding:** 1. Guangxi Innovation-Driven Development Special Project \"Research and Development and Experimental Demonstration of Key Technologies for the Synergistic Development of Water Resources Utilization and Water Ecological Industry in Typical Karst Wetlands of Lijiang River Basin\" (Guik AA20161004-1). 2. National Key Research and Development Program Project \"Research and Development and Experimental Demonstration of Key Technologies of Water Resources Regulation in Karst Wetland of Lijiang River Basin\" (2019 YFC0507502). 3.