## 4 IFC Data Model for Supporting Safety Risk Identification in Deep Excavation  
### Information Requirements for Safety Risk Identification in Deep Excavation  
Obtaining the required construction information comprehensively is important to ensure efficient safety risk identification and management. In consideration of the research objective, an information requirement model for safety risk identification (involving information, such as the title of risk events, risk factors, and specific construction parameters contributing to risk factors) should be established first. In this manner, the required construction information corresponding to certain safety risks, which is one of the critical premises of conducting automatic risk identification, can be determined. As shown in Table 1, in this research, safety risk categories--considered as the safety risk knowledge source--include technical risks, geological risks, and environmental risks [2; 6]. Other risk categories--such as risks derived from mechanical equipment failure, mishandling, or poor organization, which are indirectly related to construction safety management of deep excavation--are excluded in the first research stage. Figure 1: Research process undertaken based on the research approach. In response to the above safety risk categories, risk identification rules with corresponding risk factors should be established for risk identification. Traditionally, risk identification rules and involved risk factors are often contained in the following three sources [10; 28]: (a) empirical knowledge collected from design specifications and construction manuals, (b) theoretical knowledge obtained from statistical models in research papers, and (c) implicit knowledge of domain experts. The risk factors involved in the risk identification rules are often contributed by specific construction parameters corresponding to different construction states. Thus, in this research, the identified risk factors are described by different construction parameters. The following three steps are applied in accordance with previous studies to obtain a detailed list of risk identification rules with specific risk factors [28; 29]. In practice, the first two steps are applicable to risk events with clear definitions and mechanisms, and the third step can be used on those with uncertainties. * Step 1: Safety risk events are defined by reviewing the construction documents, through which related engineering terms can also be determined. * Step 2: Based on the reliability analysis theory, limit state functions can be established to analyze the safety risk events that can be solved with analytic models or by parsing empirical formulas. Risk factors can then be obtained from the independent variables of the limit state functions. For safety risk events where the analytical models are inapplicable, simulation models can be established using appropriate numerical methods, such that the risk factors can be obtained from the parameters of the models. * Step 3: Additional engineering expertise and practices are required to identify uncertain risk factors. * An information requirement model aiming at safety risk identification in deep excavation is established (Figure 2). As shown in Figure 2, the safety risk \"Collapse of the retaining system\" is presented as an example to illustrate the modeling principles of this information requirement model:  
1. This model consists of three layers: risk event, risk factor, and construction parameter. Different factor combinations can result in different safety risk events. Each risk factor is contributed by multi construction parameters. 2. The safety risk events considered in this model are stepwise reclassified based on the adopted construction methods, supporting systems, the three objective risk categories listed above (i.e., technical, geological, and environmental risks), and a risk list of a specific risk category. 3.