# An Established Theory of Digital Twin Model for Tunnel Construction Safety Assessment
## 7 Conclusions  
In this paper, a digital twin model of tunnel construction for intelligent safety evaluation is proposed. Moreover, a construction safety evaluation framework and modeling method are described in detail. In this study, the real space information collection technology represented by IoT and by intelligent sensor technology is used to collect data from the actual project. The virtual twin model is established by combining BIM technology, Midas technology, and the machine learning algorithm represented by LSTM. The feasibility of this method is verified by taking the arch crown settlement during tunnel construction as an example. In this paper, the main conclusions are as follows:  
* The information obtained by IoT and smart devices is the basis for establishing the digital twin model. The process and analysis of the information are the core of evaluating and predicting the construction safety status. In the face of a large number of miscellaneous construction data in the construction process, this paper uses the hierarchical method of the black box, gray box, and white box to process a large number of miscellaneous construction data. The method can reduce the workload of the virtual model building process and improve the efficiency of virtual model operation, and it meets the use requirements of the virtual twin model. It provides a reference for subsequent modeling research.
* By combining the relevant standards and specifications covered in the knowledge model, the safety evaluation and state prediction of each construction element in the construction process can be realized. The results of safety evaluation and state prediction are also the basis for the digital twin model to simulate the construction process and map the construction site in real time.  
To sum up, this paper realizes the evaluation and prediction of construction elements in the construction process through DT, which meets the dynamic requirements of the construction process. Besides, the twin models realize the digital closed-loop of safety state evaluation and prediction, which ensures that the construction process is in a safe state all the time. The safety management in the tunnel construction process is more intelligent in this paper. This study provides a new idea for intelligent safety management in the construction process.  
Conceptualization, Z.L.; Methodology, Y.Z.; Software, Y.Z.; Validation, Y.Z., N.W. and Z.L.; Writing--original draft preparation, N.W.; Writing--review and editing, Y.Z.; Project administration, Z.L.; Funding acquisition, Z.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Key Laboratory of Earthquake Engineering Simulation and Seismic Resilience of China Earthquake Administration, grant number EESSR21-02.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors would like to thank the Beijing University of Technology and the Key Laboratory of Earthquake Engineering Simulation and Seismic Resilience of China Earthquake Administration, Tianjin University, for their support throughout the research project.  
**Conflicts of Interest:** The authors declare no conflict of interest.