## 3 Frameworks and Methodologies for Research
### Methodologies for Research
#### 3.2.1 Risk Identification of TBM Construction Based on the WBS-RBS Method
In this process, the various risks that may cause accidents are classified and summarized in detail to ensure that the various safety risk factors faced in the TBM construction process can be clearly defined and presented in a clear and identifiable state. The main risks in terms of geology include collapse, sudden water influx, rock burst, and leakage of harmful gases during excavation or support processes. Therefore, factors contributing to these risks are considered to be the joint effect of the rock integrity coefficient, elastic deformation performance index, rock mass classification, internal development degree of the rock mass, moisture content of the rock mass, structural planes within the rock mass, tunnel depth, and groundwater conditions. Additionally, considering the stability, bearing capacity, and deformation characteristics from a geological perspective involves examining the presence of joints and bedding planes as well as whether they are located in an earthquake-prone zone. From a rock-properties perspective, physical properties such as abrasion resistance, frost resistance, permeability resistance, creep behavior, thermal properties, and strength are taken into account. The equipment risk factors include the type of TBM selected according to the geological conditions, the designed cutterhead structure, the cutters for different rock types, the design of different types of surrounding rock support, the selection of related auxiliary equipment, etc. The equipment risks with higher occurrence frequency include non-timely ventilation and dust removal, TBM blockage, discontinuous slagging, wear of the cutterhead or cutter, the setting of tunneling parameters inconsistent with the actual situation, etc. The influence of human-made risks in TBM construction cannot be ignored. It has a high degree of importance, because the interference and influence of human factors on TBM construction exist all the time in the construction process, and human activities exist  
Figure 2: TBM construction work breakdown structure diagram. in every construction link, so the area of human-made risks is full of uncertainty. If the organizational structure of the construction management team is unreasonable, it may lead to poor information flow and low decision-making efficiency, affect construction safety, and even lead to serious human-made risks in TBM construction. The environmental risks mainly include damage to underground pipelines, surface subsidence, groundwater pollution, and building damage. Surface subsidence is a common risk in the process of underground excavation, which may lead to different degrees of surface subsidence, and then lead to deformation and cracking of building structures. Damage to underground pipelines will lead to slow construction progress, so it is also a problem that cannot be ignored. Construction wastewater generated in the process of excavation, and the discharge of pumped leaking water, may pollute groundwater. According to the engineering RBS principle, a two-level risk decomposition is conducted for TBM construction risk sources (\(R\)). 1. Firstly, the primary Risk Breakdown Structure (RBS) for TBM construction projects and associated environmental risks comprises four categories: geological risk sources (\(R_{1}\)), equipment-related risk sources (\(R_{2}\)), human-induced risk sources (\(R_{3}\)), and surrounding environment risk sources (\(R_{4}\)). 2. Secondly, through a comprehensive analysis of TBM construction risks, and considering the decomposition direction of first-level risk sources, various secondary-level risk structures are derived from the initial structure.