## 4 Correlation Analysis of Shield Tunneling Parameters
### Correlation Analysis and Tunneling Strategy Optimization  
Based on the normal distribution test results for the shield tunneling parameters, an appropriate correlation analysis method is chosen to examine the relationship between the tunneling parameters within specific stratum sections and the overall shield interval. The correlation findings are depicted in Figure 14.  
The following can be analyzed from Figure 14:  
(1) Slurry Pressure and Grouting Pressure  
In the volcanic ash strata, the disparity between the grouting pressure and the slurry pressure typically falls within the range of 0.2 to 0.3 MPa, with the grouting pressure exceeding the slurry pressure by around 0.22 MPa (see Figure 7 for details). The slurry pressure demonstrates a positive correlation with the tunnel burial depth. It is advisable to \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Tunneling Parameters** & **Stratum I** & **Stratum II** & **Stratum III** & **Total Interval** \\ \hline Mud pressure & 0.01 & 0.01 & 0 & 0 \\ Grouting pressure & \(\surd\) (0.2) & \(\surd\) (0.2) & 0.002 & 0 \\ Grouting amount & \(\surd\) (0.2) & 0 & 0 & 0 \\ Unearthed amount & 0 & 0 & 0 & 0 \\ Total thrust & \(\surd\) (0.065) & 0.013 & 0 & 0 \\ Cutter torque & \(\surd\) (0.2) & 0 & 0 & 0 \\ Cutter speed & 0.01 & 0 & 0 & 0 \\ Excavation speed & \(\surd\) (0.144) & 0 & 0.002 & 0 \\ \hline \hline \end{tabular} Note: \(\surd\)—obeys a normal distribution; ()—normal test \(p\)-value.  
\end{table} 
Table 10: Normal distribution test results. Figure 14: Correlation analysis results of the tunneling parameters. maintain the grouting pressure approximately 0.22 MPa higher than the slurry pressure. Additionally, consideration should be given to potential ground subsidence and local uplift. Monitoring the safety of upper building structures in correspondence with ground settlement and the shield tunneling position is crucial for shallow-buried shield tunnels. This allows for timely adjustments to the grouting pressure. (2) Grouting Pressure and Grouting Amount  
In the volcanic ash strata, there exists a negative correlation between the grouting pressure and the grouting amount. The prompt and effective filling of slurry plays a crucial role in maintaining the relative stability of the soil. Should any indication of a positive correlation between the grouting pressure and the grouting amount emerge, it is imperative to conduct timely inspections of the grouting equipment to ensure smooth grouting operations and the overall safety of the shield tunneling process. (3) Total Thrust and Slurry Pressure  
In the volcanic ash strata, the total thrust is strongly negatively correlated with the mud pressure (correlation coefficient is \(-0.61\)), indicating that as the mud pressure increases, the total thrust setting will decrease, which is obvious in the \" volcanic ash debris + round gravel \" composite formation (correlation coefficient is \(-0.64\)). (4) Unearthed Amount and Total Thrust  
In the volcanic ash strata, there is a positive correlation between the unearthed amount and the total thrust. Specifically, in the composite stratum of \"clay + volcanic ash debris + round gravel\", the unearthed amount shows a moderately positive correlation with the total thrust (correlation coefficient is \(0.54\)). This correlation is significantly stronger than that observed in \"volcanic ash debris + round gravel\" and \"clay + volcanic ash debris\". (5) Cutter Torque and Total Thrust  
In the volcanic ash strata, there is a negative correlation between the cutter torque and the total thrust. Specifically, in the \"volcanic ash debris + round gravel\" composite stratum, a strong negative correlation is observed (correlation coefficient is \(-0.77\)). However, in the \"clay + volcanic ash debris + round gravel\" composite stratum, a weak positive correlation exists. The presence of clay poses a significant hindrance to shield tunneling, necessitating attention being paid to the mud cake conditions.