## 4 Engineering Application
### Application Overview  
We applied the AD_SI model to the detection of the shield tunneling process in the K section from ring 126. The shield tunneling information was obtained from real-time data collected by sensors installed on the shield machine. The sensors collected data at a sampling frequency of one sample per second. We also calculated the corresponding energy consumption based on the real-time current and voltage information of the shield machine collected during the tunneling process and the time taken to advance a unit distance. During the application of the AD_SI model, the construction parameters mainly used are the overall energy consumption of the shield machine, cutterhead torque, cutterhead rotation speed, total thrust, speed, and earth pressure. In the AD_SI model, the sliding window length for cutting the original time series is 48. Both the encoder and decoder of VAE are set with a four-layer structure, and the dimension of the latent variable is set to 6. The sliding window length for cutting the LSTM input data is set to 12, and the hidden size of the LSTM unit is set to 64. Since the input of the LSTM is the embeddings obtained from the VAE encoder and we have the LSTM model take the first \(L-1\) embeddings and predict the next \(L-1\) embeddings, the dimension of the input vector of the LSTM network is (11, 6). We collect data samples with each 5 mm advancement of the shield tunneling machine, using 2000 samples to construct the training set. In addition, we implement rolling training for the model, updating the training set when the shield tunneling machine completes one ring of advancement. We also built a base containing feature representation of three known abnormal scenarios based on historical construction projects. The known abnormal scenarios are cutter wear, mudcake event, and geological transition from soft soil to hard rock layer. The AD_SI model reported three anomalies within the K section. There were three anomalies that occurred during the actual construction process, which were located at ring 210-221, ring 231-240, and ring 258-268, respectively. Figure 5 illustrates the variation in energy consumption of this segment. It also notes the actual range of the three construction risk events and the anomalies detected by the AD_SI model. Table 1 summarizes the anomaly detection results of the AD_SI model and the corresponding actual anomalies. The AD_SI model initially detected a prolonged and continuous anomaly within the range of ring 210-221 and determined the abnormal scenario to be the geological transition. After the AD_SI model reported the anomaly, the engineers observed and analyzed the much and concluded that the geological conditions encountered by the shield machine \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Abnormal Event**} & **Actual Anomaly** & **Actual Abnormal** & **Anomaly Range** & **Abnormal** \\  & **Range** & **Scenario** & **AD\_SI Detected** & **Scenario AD\_SI Identified** \\ \hline Abnormal event 1 & ring 210–221 & geological transition geological transition geological transition & ring 210–221 & geological transition geological transition \\ Abnormal event 2 & ring 231–240 & geological transition & ring 232–240 & geological transition \\ Abnormal event 3 & ring 258–268 & mudcake event & ring 258–269 & mudcake event \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Anomaly detection and identification results of AD_SI and actual anomalies. Figure 5: The anomaly detection results of the AD_SI model and the actual range of anomalies. began to change when the shield cutterhead approached near ring 216 (corresponding to the actual ring number 210). Subsequently, the AD_SI model detected long-lasting anomalies, again starting from ring 231. It identified an abnormal scenario from ring 232 to ring 240, and the abnormal scenario was geological transition. The engineers did not pay much attention to the anomaly reported by the model at the beginning. They then noticed a significant change in parameters starting from ring 235.