# Fuzzy Synthetic Evaluation of the Long-Term Health of Tunnel Structures
## 2 Determination of the Evaluation Methods and Ideas for the Tunnel Structural Health
### Application of Fuzzy Synthetic Evaluation of Long-Term Structural Health in Cang Ling Tunnel
#### 3.4.2 The Determination of Criteria and Weight of Each Index in the Evaluation Model  
In order to scientifically evaluate the structural health status of Cang Ling Tunnel, it is necessary to establish the relationship between each index in the fuzzy synthetic evaluation model and the health level of the structure. In other words, it is necessary to establish the evaluation criteria for each factor. 1. Research on the evaluation criteria of the internal force and contact pressure for the tunnel structure. With the increase of service time of the tunnel, the primary support will deteriorate gradually, as has been mentioned before, or the bearing capacity of the primary support will gradually decrease due to corrosion and other reasons. From now on, the load of the surrounding rock will gradually transfer to the secondary lining. The secondary lining will become an important bearing unit. The safety of the tunnel structure will also be reflected in the safety of the secondary lining. Therefore, the internal force of the secondary lining is the most important information for the safety of tunnel structure during the operational period. In the tunnel structure safety evaluation system that is based on the values of the internal force of the secondary lining (the axial force and bending moment), the key point is scientifically defining the bearing capacity of the supporting structure under different safety conditions. Therefore, based on the self-designed horizontal loading device, and taking the Cang Ling Tunnel as the prototype, the authors carried out a destructive model test for the surrounding rock-supporting system of the tunnel over the entire life cycle (Figure 8) [13]. The whole test bench is \(5.34\) m \(\times\) 5.44 m \(\times\) 2.4 m, including the 3.64 m \(\times\) 3.64 m \(\times\) 0.3 m test trough and the 3 m \(\times\) 3 m \(\times\) 0.3 m model specimen. The model specimen is laid between two 25 mm thick steel plates. The upper and lower boundary of the cover plate is confined by two box beams whose sizes are 0.6 m \(\times\) 0.4 m. In order to keep the specimen in the plane strain state in the loading process, two sets of 4-6 high precision hydraulic jacks of 60 t in total are connected with the upper two boxes beam to control the vertical displacement of the specimen. The initial geostress field is achieved by eight high precision hydraulic 60-t jacks. Two jacks are applied in each direction of the load in the way of surface force through the load distribution beam. The oil pressure is driven by the air pressure through an electric pump. After using the WY-300/V type hydraulic regulator to adjust the hydraulic pressure, two sets of different loads are exported, according to the predetermined value. This system can guarantee the stability accuracy of the load applied at each level. The model test steps are as follows:  
1. In order to keep the plane strain state and reduce the friction between the test tank and the simulated surrounding rock, the upper and lower steel plate and the distribution beam are buttonted. Then the film is pasted on the upper and the lower steel plate to isolate the surrounding rock and the butter;
2. According to the different factors of surrounding rock, wires are pulled around the test tank to control the feeding quantity. After artificial leveling, a compaction rammer is used. Compacted density is controlled by the cutting ring method. The upper steel plate is lifted after compaction, then the vertical jack is installed to restrain the vertical displacement;
3. According to the initial geostress field of each section in the similarity comparison tests, the specimen is loaded with the initial geostress before the excavation of the tunnel. Then the tunnel is excavated in the middle of the surrounding rock under the initial geostress field. Rock bolts are inserted and a steel arch is installed when necessary;
4. The primary support is constructed and the pressure cells are fixed to it with cross buckles.