# An Established Theory of Digital Twin Model for Tunnel Construction Safety Assessment
## 4 Establishment of DT Construction Model
### Physical Space Information Collection Based on Internet of Things Technology  
To efficiently and accurately collect all kinds of data in the construction process, this paper proposes a construction process information collection system based on the IoT, which consists of a perception layer, a network layer, and a model layer. The physical space information collection system is based on the IoT. This system is the nervous system that connects the virtual world and the natural world to ensure the virtual twin model can be continuously updated to reflect changes in the real world (such as position, distance, speed, acceleration, direction, etc.). Data information, and data analysis, thereby guide the safety management of construction processes in the physical world. The perception layer comprises a Radio Frequency Identification System (RFID), 3D scanners, various sensors, and other technologies. Once the construction starts, the  
Figure 4: Actions and sub-actions of phase 2.  
perception layer begins to collect multiple data, and different technologies can realize real-time monitoring of humans, machines, material, method, environments, and other factors. The perception layer realizes the conventional perception of the whole construction process, which is the basis of the information collection system. The transport layer is the embodiment of the system data transmission. It realizes the real-time interaction between twin models and physical entities. There are two-way transmissions of data information as the path. Data transmission can be implemented by a combination of wired and wireless. This method ensures the data can be quickly, stably, and safely transmitted through a two-way route between the perception layer and the model layer. Data transmission is achieved through IoT communication technologies such as LoRa, Wi-Fi, Zigbee, Bluetooth, and 5G. Considering the characteristics of tunnel construction, it is recommended to use LoRa as the main transmission technology. The information acquisition of the physical space provides the basis for establishing the virtual model and the evaluation of the safety state of the construction process, by arranging sensors and other monitoring instruments in the physical space to complete the information collection and then transmitting the data to the virtual model side through the network layer, thus laying the foundation for the establishment and updating of the model. On this basis, the process of simulation is established, which realizes analog synchronization between the digital world and the physical world during construction. The simulation is carried out through the virtual model to analyze and predict the construction process's safety state. The information collection process based on the IoT is shown in Figure 5.  
As mentioned in Section 4.1 above, the tunnel construction process involves much information and data, which should be screened and sorted out during the modeling process. In this section, all the related information will be processed in mathematical expressions from the perspectives of men, machines, materials, and the environment. The status information of construction personnel mainly includes location and health information. The mathematical expression to obtain the status information of construction workers is as follows:  
\[PI_{i}=(ID_{i},LI_{i},HS_{i}) \tag{3}\]  
In the above formula, \(PI_{i}\) represents personal information; \(ID_{i}\) represents personal identity information, which includes the information of name, job number, position type of job, etc. ; \(LI_{i}\) represents the location information of personnel; and \(HS_{i}\) represents the health information of personnel, including heart rate, etc. All the information is obtained by intelligent helmets. Figure 5: Information collection process based on the IoT. All sorts of sensors for information collection in the perception layer and construction equipment are called intelligent equipment.