## 4 IFC Data Model for Supporting Safety Risk Identification in Deep Excavation
### Safety Risk Identification Using the CRIS Prototype  
The effectiveness of the IFC data model-based safety risk identification approach is evaluated by conducting a case study in the background of a typical deep excavation project, using the CRIS prototype. It is a commercial building construction engineering in Zhengzhou, China, with an 18-storey upper structure and a 2-storey substructure. The excavation depth of this building project measures up to 10.5 m. Soil nailing walls and pile anchors are utilized as a combined bracing system, and a light-well-point system is adopted as the dewatering method. When the opencut method is adopted, the deep excavation process can be divided into six phases: (1) preconstruction, (2) retaining structure establishment, (3) foundation treatment and dewatering, (4) foundation pit excavation, (5) main structure construction, and (6) foundation pit backfill. In this case study, safety risk identification in the foundation pit excavation phase is emphasized. The workflow of the safety risk identification process using the CRIS prototype is shown in Figure 12.  
Figure 12: Workflow of the safety risk identification using CRIS.  
* IFC file generation Based on the input construction plan and the IFC data model, a basic deep excavation information model was established in RevitTM. The primary structure components, such as retaining piles and enclosing purlins, were expressed by entity objects defined in IFC4. For the subordinate components--such as soil nails, anchor bolts, and dewatering wells--their relevant component families with specific attributes were created. Then, these component families were added to the project file to express the corresponding subordinate components. The correctness and completeness of the required information defined above were identified, and the necessary custom property sets were introduced into the model by deriving the IFC file from RevitTM and importing it into ArchiCADTM. Then, necessary custom property sets were added to corresponding primary structural components to output a complete IFC file based on the IFC data model. When the IFC file was input into the CRIS prototype, a new project record was created.
* Risk identification and result output After choosing the foundation pit excavation phase, a potential safety risk list was created in accordance with the construction methods adopted in this project. The information involved in the list contained potential safety risk events, related factors, and required construction parameters. Based on the potential safety risk list, the required construction parameters were extracted from the IFC files. Moreover, relevant construction parameters were input by users according to the dynamic construction sites and information requirement list output by the CRIS prototype. Then, the system initiated the safety risk reasoning and identification process. Figure 13 takes soil flow in the bottom of the foundation pit as an example to illustrate the output results.  
Figure 13: Safety risk identification results from the CRIS prototype (safety risk of soil flow in the bottom of the foundation pit).