With the subsection implementation of Yunnan-Tibet railway project, the planning and design of Lijiang-Shangri-La section has been put on the agenda. However, due to the complex topographic and geological conditions, it is still difficult to determine the route after several rounds of argumentation. According to the preliminary plan (figure 13- 1), there are three route selection schemes for Lijiang-Shangri-La section of Yunnan-Tibet Railway: ① Lijiang-Changsongping-Hutiaoxia Upper and Lower Exit-Shangri-La scheme (western route scheme); ② Lijiang-Daju-Baishuitai-Xiaozhongdian-Shangri-La scheme (combined scheme); ③ Lijiang-Daju-Baishuitai-Tianshengqiao-Shangri-La Scheme (Eastern Route Scheme). According to the preliminary analysis, the west route scheme has good engineering geological conditions and can be recommended. In this scheme, 34 new railway tunnels are required, with a total length of 87 130 m, accounting for 54.4% of the total length of this section. The longest tunnel is the Yufeng Temple Tunnel in the northwest of Lijiang, with a total length of10970 m. There are 39 railway bridges (10253 m) and 82 culverts (4,547m) to be built, accounting for 9.2% of the total length of the line. The complex engineering geological conditions make the scheme still have many problems, and the engineering construction is difficult.

In order to better guide the route selection of this section of railway, on the basis of regional crustal stability evaluation, we introduce the analytic hierarchy process based on GIS technology into the engineering geological stability evaluation (engineering geological condition evaluation) of Lijiang-Shangri-La railway planning area. In the evaluation process, the factors such as terrain slope, engineering geological rock group, slope structure, geological disaster development, crustal stability, micro-landform type (height difference between terrain and railway design), human engineering activities, precipitation, distance from river valley and so on are comprehensively considered, and the advantages of GIS technology in processing massive data information are fully utilized, and the analytic hierarchy process model is used to evaluate the engineering geological stability of Lijiang-Shangri-La railway planning area. According to the evaluation results, it can guide the comparison and optimization of this section of the line.

Second, the principle of analytic hierarchy process based on GIS

Analytic Hierarchy Process (AHP) is a systematic analysis method combining qualitative analysis with quantitative analysis, which was put forward by American mathematician Sattyt L. in 1970s. It is suitable for decision analysis of multi-criteria and multi-objective complex problems, and can quantify the decision-making thinking process of decision-makers on complex systems, thus providing a basis for choosing the optimal decision (Figure 13-2). After years of application practice, many researchers began to combine GIS technology with AHP method, which greatly improved the application effect of traditional AHP method in geoscience research (Harris et al., 2000; Liu Zhenjun, 20065438+0; Peng et al., 2005). The analytic hierarchy process based on GIS makes full use of the spatial classification and spatial analysis functions of GIS technology, and has obvious advantages in the collection, processing and automatic drawing of evaluation index data. Not only can the related influencing factors of engineering geological stability be analyzed in more detail, but also the evaluation results are more intuitive and convenient for application without the limitation of the number of calculation units in the calculation process.

Figure 13- 1 Schematic Diagram of Lijiang-Shangri-La Section of Yunnan-Tibet Railway

Figure 13-2 Technical Roadmap of Analytic Hierarchy Process Based on GIS

The zoning evaluation process of engineering geological stability based on GIS analytic hierarchy process can be roughly divided into the following steps:

(1) Determine the research area, research object and research goal, conduct data analysis, and determine the data required for engineering geological stability zoning, including data sources and data quality indicators.

(2) Data processing of collected data, including digitization, format conversion, projection conversion, layering and attribute coding. On the MapGIS 6.7 software platform, the spatial database of research area and research object is established.

(3) According to the characteristics of the research target, the factors affecting the target are analyzed, the hierarchical index model and hierarchical structure of the target are established, and the judgment matrix is constructed. Experts comprehensively score the impact factors, sort the graded list, solve the weight vector and check the consistency, so as to get the values of each index factor, and extract the analysis factors by using the spatial analysis function of GIS.

(4) Using ArcGIS 9.2 software platform, the evaluation area is rasterized, and each grid is regarded as an operation unit of model evaluation, and the data in the database is rasterized according to the rules. Then, the model evaluation method of graphic superposition is used to assign the weights of various factors involved in the evaluation to different grids. Each factor is graphically superimposed, and the attribute value is calculated algebraically. Then, the superimposed grid is digitized to generate new graphics and form the final evaluation result.

(5) Mathematical model for zoning evaluation of engineering geological stability:

Crustal stability and main engineering geological problems along Yunnan-Tibet railway

In which: b-engineering geological stability index, AJ-weight, NJ-index.

(6) Through the analysis and calculation of the distribution range of engineering geological stability index values, combined with the field investigation results, comprehensively evaluate the suitability of railway engineering construction in different regions.