Comparative Analysis of ARIMA and LSTM Model-Based Anomaly Detection for Unannotated Structural Health Monitoring Data in an Immersed Tunnel

Structural Health Monitoring (SHM) systems have become a crucial tool for the operational management of long tunnels. For immersed tunnels exposed to both traffic loads and the effects of the marine environment, efficiently identifying abnormal conditions from the extensive unannotated SHM data presents a significant challenge. This study proposed a model-based approach for anomaly detection and conducted validation and comparative analysis of two distinct temporal predictive models using SHM data from a real immersed tunnel. Firstly, a dynamic predictive model-based anomaly detection method is proposed, which utilizes a rolling time window for modeling to achieve dynamic prediction. Leveraging the assumption of temporal data similarity, an interval prediction value deviation was employed to determine the abnormality of the data. Subsequently, dynamic predictive models were constructed based on the Autoregressive Integrated Moving Average (ARIMA) and Long Short-Term Memory (LSTM) models. The hyperparameters of these models were optimized and selected using monitoring data from the immersed tunnel, yielding viable static and dynamic predictive models. Finally, the models were applied within the same segment of SHM data, to validate the effectiveness of the anomaly detection approach based on dynamic predictive modeling. A detailed comparative analysis discusses the discrepancies in temporal anomaly detection between the ARIMA- and LSTM-based models. The results demonstrated that the dynamic predictive modelbased anomaly detection approach was effective for dealing with unannotated SHM data. In a comparison between ARIMA and LSTM, it was found that ARIMA demonstrated higher modeling efficiency, rendering it suitable for short-term predictions. In contrast, the LSTM model exhibited greater capacity to capture long-term performance trends and enhanced early warning capabilities, thereby resulting in superior overall performance.