# An Established Theory of Digital Twin Model for Tunnel Construction Safety Assessment
## 4 Establishment of DT Construction Model
### Establish Virtual Model  
#### 4.3.1 Data Integration Model  
In the process of establishing the DT model, the twin model is often divided into four levels: \"geometry model, physics model, behavior model and rules model\" [37]. Through the information collection of actual objects in the physical world, the information collected and the model established are completed. The multi-level and high-precision simulation of the actual construction process is realized by associating and integrating various dimensional models. BIM has been widely used in construction in recent years. BIM has the advantages of high precision, complete information and multi-dimensional visualization, which can be very competent for the establishment of a geometric dimension model of twin models. Establishing geometric models by BIM can realize the data visualization of the construction process, which lays a foundation for the establishment of other dimension models. BIM modeling software such as Revit can be selected to complete the establishment of the geometric model. The high-precision BIM model can reflect the geometric characteristics of the construction process, and it can be a suitable carrier of the basic information of various construction materials and components. However, due to the complexity and variability of the actual construction process, it is difficult to ensure that the actual construction process is entirely consistent with the BIM model [38]. To reduce the error between the BIM model and the actual construction process, 3D scanning technology is used to capture the actual construction state. The 3D scanning needs to obtain the point cloud data model of the construction process firstly, then establish the point cloud model and integrate the point cloud with the BIM model. Combining the point cloud model and BIM model can adjust the geometric model in time, which improves the accuracy and precision of the geometric model [39]. After the point cloud data is obtained, the abnormal data caused by machine error and external factors in the scanning process are deleted by denoising. The adjusted BIM model can more accurately reflect the geometric characteristics of the construction process and provide a basis for the adjustment of the physical model, thus improving the accuracy of the physical model. At the physical level, the physical characteristics of construction objects are mainly simulated through finite element analysis software such as MIDAS. The construction object's mechanical performance is affected and calculated on this basis of finite element analysis, combined with the sensor equipment's data. In the actual construction process, the geometric dimensions of the building components impact the mechanical properties. Therefore, high-precision geometric models can improve the finite element analysis' accuracy and the reliability of physical models. The behavior model proposed by [PERSON] is mainly used to describe the real-time response and behavior of entity objects under the set operation mechanism, such as evolutionary behavior, performance degradation behavior, etc., which is commonly achieved by machine learning [18; 37]. The rule model is established and combines the behavior rules of entity objects with relevant standards and specifications [18; 37]. The purpose of the rule model is to evaluate and predict the performance of entity objects in the future. Generally, it is generated by integrating existing knowledge and machine learning algorithms to continuously evolve and mine. As mentioned above, the behavior model and rule model have certain similarities and close connections. The rule model provides guidance for the behavior model, and the behavior model and rule model are both inseparable from machine learning algorithms. Therefore, this paper integrates the two models into one model through the Data-to-Information-to-Knowledge-to-Wisdom Model (DIKW) hierarchy theory. The integrated model is called the knowledge model.