## 5 Engineering Applications  
### Numerical Simulation of Slopes  
Natural gas, as a kind of clean energy, has been widely used in civil and industrial fields due to its good economy and environmental protection. Piles AA001-AA004 of China-Russia East Line Natural Gas Pipeline is a controlled project of transit section, located in Heihe City, Heilongjiang Province. The geographical coordinates of Piles AA001-AA004 are between 127\({}^{\circ}\)21\({}^{\prime}\)24\({}^{\prime\prime}\) and 127\({}^{\circ}\)21\({}^{\prime}\)06\({}^{\prime\prime}\) east longitude and 50\({}^{\circ}\)17\({}^{\prime}\)30\({}^{\prime\prime}\) and 50\({}^{\circ}\)17\({}^{\prime}\)24\({}^{\prime\prime}\) north latitude. The monitoring area belongs to the landform of low mountains and hills. The ground elevation in the area is 95-290 m, while the relative elevation difference is 150-200 m. The cutting depth of the valley is 80-120 m. The monitoring area is characterized by cold temperate continental monsoon climate, with warm and rainy summer. The locations of the Pile AA001-AA004 and the monitoring slope are shown in Figure 8a. The slope angle is about 40\({}^{\circ}\), the total length of the horizontal distance of the slope is 477 m, and the height difference is about 120 m. The slope body is mainly composed of a sand-gravel layer on the surface and strong weathered andesite. The surface of the monitoring area is exposed in a large area, and the surface layer is mainly composed of sandy gravel. The second layer is breccia and gravel layer, mainly consists of strong weathered andesite, with a particle size of 0.5-5 cm. The joints and fissures are relatively developed. The groundwater in the monitoring area is divided into two types, namely, loose accumulation pore water and bedrock fissure water. The loose accumulation pore water is recharged by atmospheric precipitation and river water in the region, which is greatly affected by seasons. The recharge is abundant in rainy seasons. Bedrock fissure water is only recharged by atmospheric precipitation. It is necessary to conduct a slope stability analysis since the stability of the slope covered by the natural gas pipeline directly affects the stability of oil and gas transportation. According to the hydrogeological data in the field, the stability of the slope is evaluated and the FOS of the slope is calculated based on the numerical simulation method. A simple model of the landslide in the monitoring area is established in the leading software for slope stability calculation. The coordinates of the control points of each structural layer are input with the landslide foot as the origin, and the established model is shown in Figure 8b. The shear strength of rock and soil in the monitoring area of the first section of entry in Table 6 is used as the calculation parameter, and the calculation is carried out according to different moisture contents. The calculation method is to automatically search for the most dangerous sliding surface, and the step length is 1 m. After the dangerous sliding surface is determined, the step length is reduced to continue calculating the FOS. The safety factors are shown in Table 7. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Model**} & **Positive Ideal** & **Negative Ideal** & **Comprehensive** & \multirow{2}{*}{**Ranking**} \\  & **Solution** & **Solution** & **Score** & \\ \hline RF & 0.0188 & 0.1052 & 0.8482 & 1 \\ DT & 0.1175 & 0.0113 & 0.0877 & 8 \\ SVM & 0.1061 & 0.0185 & 0.1484 & 7 \\ GBDT & 0.0354 & 0.0958 & 0.7301 & 3 \\ KNN & 0.1011 & 0.0219 & 0.1782 & 6 \\ Adaboost & 0.0923 & 0.0310 & 0.2513 & 5 \\ Bagging & 0.0701 & 0.0522 & 0.4270 & 4 \\ ANN & 0.0220 & 0.1163 & 0.8410 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Ranking results based on critic-TOPSIS method. In the situation of low water content (6%) and high water content (25%), the slope in the monitoring area tends to slide in shallow layers along the interface between soil and rock layers.