## 5 An Intelligent Shield Attitude Correction Method  
As the BOTA-LSTM model can reasonably predict the multi-ring shield attitudes, an intelligent shield attitude correction method is then proposed based on the BOTA-LSTM model. The monitoring data from rings 413 to 453 in Figure 10 shows that the actual shield attitude deviation exceeds the range of \(\pm\)50 mm required by the code for construction and acceptance of metro engineering, indicating a need for correction of the shield attitude. The horizontal deviation of shield attitude is defined as negative for left and positive for right attitudes. The detailed process of the shield attitude correction method is shown in Figure 14.  
Figure 12: Comparison of ten results of LSTM and GRU models.  
Figure 13: Comparison of Bayesian hyperparameter optimization for GRU and LSTM models. (**a**) loss distribution and (**b**) optimization path.  
First, the proposed BOTA-LSTM model is applied to predict the attitude and total thrust for the next five rings (rings 1 to 5). The model predictions are analyzed to check if the shield attitude deviates beyond the \(\pm\)50 mm range. If any of the five rings express an attitude deviation exceeding 50 mm, it requires an adjustment in the shield construction parameters. The adjustment range of the shield construction parameters is shown in Table 11. It is noted that shield construction parameter adjustments should consider a comprehensive analysis of the total thrust predictions and geological survey reports.  
Using the adjustment of oil pressure as an example, if the shield machine transitions from hard rock to soft soil and the predicted values of total thrust show an unreasonable increase in the predicted values of total thrust, and subsequently, the shield machine deviates towards the right, the oil pressure in zones A# and B# should be reduced accordingly. Conversely, when moving from soft soil to hard rock with a decreased total thrust prediction, if the shield machine still deviates towards the right, the oil pressure in A# and B# should be increased. If the predicted attitude for all five rings is within the \(\pm\)50 mm range, the focus is then placed solely on the total thrust. If the total thrust is excessively high, a reduction in oil pressure in zones A#, B#, D#, and E# should be implemented. When it is found that the  
Figure 14: Process of parameter tuning for shield attitude correction.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Shield Construction Parameter** & **Value Range** \\ \hline A\# oil pressure (bar) & 0–200 \\ B\# oil pressure (bar) & 0–200 \\ C\# oil pressure (bar) & 0–200 \\ D\# oil pressure (bar) & 0–200 \\ E\# oil pressure (bar) & 0–200 \\ F\# oil pressure (bar) & 0–200 \\ Advance rate (mm/min) & 0–30 \\ Total thrust (kN) & 0–80,000 \\ Torque (kN\(\cdot\)m) & 0–25,000 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Adjustment ranges of the shield construction parameters.  
predicted shield attitudes for rings 1 to 5 are all within a range of \(\pm\)50 mm, and the total thrust has been adjusted appropriately, the shield machine can move one ring forward, and then the attitudes and total thrusts of next five rings (rings 2 to 6) can be predicted.  
Figure 15 shows the comparison before and after the correction of the shield attitude. Specifically, the HDSH of the shield machine is 4 mm, with a total thrust of 60,739 kN at ring 412. The predicted HDSH for ring 417 is -61 mm, indicating a leftward deviation of the shield attitude, and the shield machine is transitioning from a harder rock to a softer soil layer, with an increasing total thrust. At this time, the changes in total thrust do not match with the changes in the geological strata. Therefore, it is necessary to adjust the shield attitude in advance and reduce the total thrust. The results of the corrections