## 3 Frameworks and Methodologies for Research
### Methodologies for Research  
#### 3.2.1 Risk Identification of TBM Construction Based on the WBS-RBS Method  
One of the key factors in conducting TBM construction risk analysis is to determine the influential factors and establish a rational and effective risk index system [19]. In project management, the work breakdown structure (WBS) is a crucial concept that involves systematically dividing the construction process into a well-defined hierarchical framework. On the other hand, the risk breakdown structure (RBS) is a technique used to progressively categorize potential risks originating from major sources into more specific risk factors until they become negligible [20]. [PERSON] et al. [21] were the first to combine the WBS and RBS methods, constructing a WBS-RBS risk identification coupling matrix for projects, identifying project risk factors, and establishing a project's risk index system. In tunnel TBM construction project risk management, according to the site environment and risk management design requirements, the target and limit of risk identification are preliminarily determined. For TBM construction of the tunnel, the goal of risk identification mainly refers to whether safety accidents will occur during TBM construction, including but not limited to equipment failure, casualties, environmental pollution, etc. The boundary of risk identification is more extensive, from the preparation work before TBM construction to the work in TBM excavation construction, etc., for example, in the early stage of TBM construction, the equipment needs to be comprehensively inspected and debuggable to ensure its safety and reliability. It is also necessary to conduct systematic safety education and skill training for personnel to improve their safety awareness and operational skills. In the normal driving process, all parameters should be monitored in real time. In the initial support stage, it is necessary to strengthen the tunnel support in time to avoid a collapse caused by groundwater flooding or rock mass loosening. As for the auxiliary construction stage, such as drainage, ventilation, and transportation, it is also necessary to pay attention to problems such as equipment failure and personnel injury. 1. Establish the work breakdown structure for TBM construction [22; 23; 24; 25; 26; 27]. The WBS work breakdown structure method is founded on system engineering theory, enabling the gradual subdivision of a complex and extensive TBM tunnel project. Based on management content, it is divided into a single operational process, further disintegrating the TBM construction project into multiple work units that possess excellent controllability and operability. According to the Work Breakdown Structure (WBS) principle, the TBM construction process (\(W\)) is divided into two levels:  
1. Based on the TBM construction process, the first level of the WBS is further decomposed into four stages: TBM construction preparation (\(W_{1}\)), TBM tunneling construction (\(W_{2}\)), TBM preliminary support (\(W_{3}\)), and TBM auxiliary equipment construction (\(W_{4}\)). The stage of TBM construction preparation primarily refers to the preparatory phase when the TBM enters the tunnel excavation. 2. According to the operation conditions of each process of TBM construction, the first-level WBS is adjusted and optimized according to the characteristics of the process to form a more detailed second-level WBS, which is specifically the operation unit, and intuitively indicates that the first-level construction stage is composed of various second-level operation units. The obtained decomposition structure for TMB construction work using WBS method is illustrated in Figure 2.  
Establish the decomposition structure of TBM construction risk sources [28; 29; 30; 31]  
By using the RBS method, the potential risks in the TBM construction process are analyzed layer by layer, and a complete risk decomposition tree is established.