## 3 Example Analyses  
### Overview of Maji Hydropower Station and Classification Standards and Parameters  
Maji Hydropower Station is located in Mujiajia Village, Maji Township, Fugong County, Yunnan Province (Figure 3). The proposed dam site is a concrete double-curvature arch dam with a design height of 300 m. The project area is located southeast of the Qinghai-Tibet Plateau and belongs to the Hengduan Mountains in western Yunnan. The terrain is generally high in the north and low in the south. The dam site area mainly develops into alpine canyons. The mountains on both sides of the river are distributed above 3000 m-4000 m, and the relative height difference is 1500 m-2500 m, which belongs to the alpine canyon geomorphic unit. The overall flow direction of Nujiang River is roughly SE130\({}^{\circ}\)-SE170\({}^{\circ}\). The valley slopes on both sides are steep, and the slope is generally 45\({}^{\circ}\)-60\({}^{\circ}\). The cliffs are more common, showing a symmetrical 'V' shape (Figure 4). The strata in the area are relatively developed and are exposed from Proterozoic to the Quaternary. The metamorphic deformation of the strata is quite different. The changes in lithology and lithofacies are extremely complex. Magmatic, metamorphic, and sedimentary rocks are all exposed (Figure 5). The groundwater in the reservoir area mainly includes bedrock fissure water and loose rock pore water, mainly bedrock fissure water. According to Reference [35], an engineering geological classification scheme of the dam foundation rock mass was carried out. The quantitative standard of rock mass quality classification of the Maji hydropower station was determined, as shown in Table 2.  
Figure 4: Geomorphology and geology of the dam site. Figure 3: Traffic location diagram of Maji hydropower station. The evaluation of rock mass quality is closely related to the selection of evaluation indexes. These indexes mainly include geological factors and engineering factors. Geological factors include rock mass characteristics, stress state and joint surface distribution. Engineering factors refer to the external factors that are artificially formed in the later period of rock mass without disturbance. The rock mass quality evaluation index is very complex and diverse. In this paper, the rock mass quality evaluation index is determined according to the geological environment of the actual project, focusing on the study of rock mass characteristics before engineering activities. Based on the widely used specifications, combined with previous experience and a comprehensive consideration of the relevant literature, the rock mass quality classification of PD105 is taken as an example in this paper. Five evaluation indexes were used: saturated compressive strength (\(C_{1}\)/MPa), fracture spacing (\(C_{2}\)/m), acoustic wave velocity (\(C_{3}\)/m/s), RQD (\(C_{4}\)/%) and integrity coefficient (\(C_{5}\)) of rock [10; 35; 36; 37]. The weight of each evaluation index was determined by game theory, and the K-PSO clustering algorithm was used to evaluate the rock mass grade. The quality evaluation indexes of the rock mass are as follows (Figure 6). 1. Rock uniaxial saturated compressive strength \(R_{c}\) (MPa) reflects the degree of hardness of rock and rock characteristics. 2. Structural plane spacing \(J_{d}\) (m) represents the characteristics of the geological structure and rock mass structure. 3. Acoustic wave velocity \(V\) (m/s) can comprehensively reflect rock mass quality. 4. The RQD index reflects the size and integrity of rock mass. 5. Integrity coefficient \(K_{v}\) can be used to classify the rock mass integrity. Considering that the units of each evaluation factor are different, the classification criteria are dimensionless to eliminate the dimension of the index. The dimensionless treatment formulae are shown in Equations (18) and (19):  
Benefit indicators:  
\[A=(M-M_{min})/(M_{max}-M_{min}) \tag{18}\]