## 4 Numerical Analysis of a High Rock Temperature Tunnel
### Result Analysis  
To validate the aforementioned numerical model, the comparison between the calculated and measured temperatures at the BD3Z-85 and JWZ-1 boreholes is given in Figure 18. Obviously, the variation trends of the calculated and measured temperatures are nearly identical. However, there are some deviations between the computed temperatures and the measured data at some measuring points. In Figure 18a, the calculated temperature is generally approximately 3 \({}^{\circ}\)C higher than the measured value. This is because the rock mass in the numerical analysis is treated as a continuous medium, while the actual rock mass has many beddings and joints, which play the role of thermal resistance to some extent. The borehole depth of JWZ-1 is 120 m. It is obvious from Figure 18b that the measured temperature is greater than the calculated temperature within 78.5 m and that the maximum difference is approximately 6 \({}^{\circ}\)C. Below a depth of 78.5 m, the calculated value is greater than the measured value. Because the JWZ-1 borehole is located on the F2-6 fault (as shown in Figure 15), which is a thermal conductivity fault, the temperature rises within a certain depth range. The fault has a significant influence on the temperature field. Therefore, in the process of tunnel line selection, the thermal fault should be explored or the line should be kept away from the thermal fault as much as possible. Nevertheless, most parts of the two curves are in good agreement.  
To further validate the numerical model, the temperature values of the shoulder and hole bottom were derived from the numerical analysis using the coordinate relationship and compared to the corresponding measured values (as shown in Figure 19). The calculated temperature variation rule is basically consistent with the measured temperature variation rule at the road shoulder and hole bottom. However, there are differences between the calculated and measured values at individual locations. As shown in Figure 19a, the calculated value at the shoulder of the JWZ-1 borehole is 5.9 \({}^{\circ}\)C less than the measured value, which is 12.12% of the measured value. This is mainly affected by the thermal conductivity fault F\({}_{2-6}\). At the road shoulder and bottom of the BD3Z-95 borehole, the measured temperature is lower than the calculated temperature by 4.9 \({}^{\circ}\)C and 6.9 \({}^{\circ}\)C, respectively, which is 27.37% and 38.67% of the measured value. As seen from the figure, the BD3Z-95 borehole is located in the F\({}_{1-1}\) fault, which is a thermal insulation fault and  
Figure 17: Finite element meshes.  
Figure 18: Comparison between the computed and measured temperatures: (**a**) at the BD3Z-85 borehole and (**b**) at the JWZ-1 borehole.  
can prevent heat transfer. Therefore, the railway lines can be chosen to cross the insulation fault as much as possible.  
Through calculation, the maximum ground temperature in the direction of the Jiwox-iga tunnel line is 52.5 \({}^{\circ}\)C, the tunnel length with the ground temperature exceeding 28 \({}^{\circ}\)C accounts for 96.25% of the total tunnel length, and the length of the tunnel with a ground temperature higher than 45 \({}^{\circ}\)C is nearly 1200 m, as shown in Figure 20. After the excavation of the tunnel, the temperature of the tunnel face at a distance of 234-488 m from the right portal was measured, and the calculated temperature was compared with the measured value (as shown in Figure 20). The variation law of the calculated values is basically the same as that of the field measurements. However, a stage when the measured temperature dropped sharply was observed. The reason for this is that the air drill is drilled with water in the excavation, and the measures of spray watering and ventilation are adopted in the tunnel in advance, so the temperature of the tunnel face is reduced.  
Figure 19: Comparison between the calculated and measured temperatures: (**a**) at the road shoulder and (**b**) at the bottom of the boreholes.