## 3 Design Analysis of Curtain Grouting
### Result Analysis
#### 3.2.5 Internal Force Analysis of Secondary Lining  
The internal force of the secondary lining is an important indicator for analyzing and evaluating the safety of the structure. The axial force diagram of the secondary lining arch crown (Table 15) shows that when the secondary lining concrete reaches the design strength, the axial force of the lining structure will increase significantly after bearing the remaining surrounding rock pressure. Under the conditions of no curtain grouting and curtain grouting, respectively, the maximum axial forces reach 42.84 kN and 29.09 kN. When the measuring point of the arch crown is more than 21 m away from the palm surface, the axial force area tends to be stable, with a slight decrease generally valued at approximately 4 kN. Secondly, the maximum difference between the axial force of the secondary lining under the condition of no curtain grouting and the axial force of the arch crown under the condition of curtain grouting is around 10 kN, with a difference in the axial force values under the two conditions of approximately 25%, thus indicating the ability of curtain grouting to comprehensively enhance the secondary lining's safety reserve or improve the secondary lining stress. Table 16 shows the variation in the bending moment stress at each measuring point of the secondary lining arch crown. The certain similarity in the stress trend between the secondary lining bending moment and the axial force is reflected as follows: the secondary lining bending moment under the condition of no curtain grouting firstly reaches the maximum at 38.39 kN.m and then slightly decreases to 34.12 kN.m. Meanwhile, the secondary lining bending moment with curtain grouting firstly reaches the maximum of 30.72 kN.m, and then slightly decreases to 27.30 kN.m. Secondly, the maximum difference \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**The Advance Progress of**} & \multicolumn{1}{c}{**18**} & \multicolumn{1}{c}{**21**} & \multicolumn{1}{c}{**24**} & \multicolumn{1}{c}{**27**} & \multicolumn{1}{c}{**30**} & \multicolumn{1}{c}{**33**} & \multicolumn{1}{c}{**36**} \\ \multicolumn{1}{c}{**Heading Face (m)**} & & & & & & & & & \\ \hline A-1 & 9.27 & 39.45 & 42.84 & 41.98 & 40.81 & 39.43 & 38.78 \\ B-1 & 0.00 & 20.35 & 31.00 & 33.51 & 32.09 & 31.61 & 30.96 \\ C-1 & 0.00 & 0.00 & 18.63 & 30.20 & 33.15 & 32.30 & 31.98 \\ D-1 & 0.00 & 0.00 & 0.00 & 19.35 & 31.48 & 34.27 & 33.95 \\ E-1 & 0.00 & 0.00 & 0.00 & 0.00 & 19.81 & 31.78 & 35.62 \\ A-2 & 9.27 & 29.59 & 32.13 & 31.48 & 30.61 & 29.57 & 29.09 \\ B-2 & 0.00 & 15.26 & 23.25 & 25.13 & 24.06 & 23.71 & 23.22 \\ C-2 & 0.00 & 0.00 & 13.97 & 22.65 & 24.86 & 24.23 & 23.99 \\ D-2 & 0.00 & 0.00 & 0.00 & 14.51 & 23.61 & 25.71 & 25.46 \\ E-2 & 0.00 & 0.00 & 0.00 & 0.00 & 14.85 & 23.83 & 26.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Axial force trend of secondary lining arch crown (Unit: kN). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**The Advance**} & \multicolumn{1}{c}{**6**} & \multicolumn{1}{c}{**9**} & \multicolumn{1}{c}{**12**} & \multicolumn{1}{c}{**15**} & \multicolumn{1}{c}{**18**} & \multicolumn{1}{c}{**21**} & \multicolumn{1}{c}{**24**} & \multicolumn{1}{c}{**27**} & \multicolumn{1}{c}{**30**} & \multicolumn{1}{c}{**33**} & \multicolumn{1}{c}{**36**} \\ \multicolumn{1}{c}{**Heading Face (m)**} & & & & & & & & & & & \\ \hline A-1 & \(-111.6\) & \(-138.0\) & \(-  
between the bending moment of the secondary lining without curtain grouting and the bending moment of the arch crown with curtain grouting is around 7.67 kN. The difference in bending moment values under the two conditions is around 20%. Therefore, the curtain grouting scheme can effectively increase the safety reserve of the secondary lining support and ensure the stability and durability of the tunnel lining structure.