# Risk Assessment Method and Application for Tunnel Lining Demolition Construction
## 2 Risk Index Framework for Tunnel Lining Demolition Construction
### Identification and Determination of Risk Indicators  
The task of risk identification for tunnel lining demolition construction is to distinguish and classify the risk factors hidden in each link of tunnel lining demolition construction by using effective risk identification methods so that the managers can identify the existing risk factors and the impact these risk factors may have on the whole construction process, and preliminarily rank the risk factors, so as to determine the main risk factors [27]. The general risk identification process includes determining the risk identification objectives, identifying the most important project participants, collecting data, estimating the form of project risk, and identifying potential project risks. The identification steps of tunnel lining demolition construction risk also follow such a process [28]. According to the example of the tunnel lining demolition project, the demolition process is comprehensively analyzed. Based on the opinions of relevant experts, it is mainly divided into five aspects: geological conditions, tunnel design, lining state, construction method, and construction organization. The influencing factors of tunnel lining demolition construction are analyzed from these five aspects:  
(1) Geological conditions  
The grade of surrounding rock, groundwater, and in situ stress are mainly considered. The surrounding rock of the tunnel is subject to secondary disturbance and sudden reduction in radial support force (especially the weak initial support of the tunnel or the removal section of the initial support) during the demolition of the existing structure. The surrounding rock is prone to instability and collapse, especially in the broken section of the surrounding rock. The surrounding rock is classified according to the integrity of rock mass and rock strength. The weak and broken surrounding rock is prone to large deformation, and the corresponding lining structure is different, which also determines the pretreatment measures before demolition [29]. Water-rich areas and high ground stress conditions are large, which are prone to mud and water inrush, and the corresponding demolition risks are also very different. (2) Tunnel design  
The lining structure and tunnel section are mainly considered. The lining structure is mainly divided into plain concrete and reinforced concrete. The removal of plain concrete is relatively easy, and the removal of reinforced concrete has good integrity. The removal of reinforced concrete has a large mutual disturbance, and the corresponding construction risks are different. The tunnel section has various forms, such as a rectangle, circle, horseshoe, etc. ; the section curvature affects the stability of the lining structure, and the risk of demolition operation is also different [30]. (3) Lining state  
Service time, structural deterioration, maintenance period, and lining defects are mainly considered. Generally, the existing tunnel lining structure that needs to be de molished has very serious quality defects or structural diseases [31], which is a major potential safety hazard, making it very prone to safety accidents in demolition operations. The defects of the lining itself refer to the structural problems caused by nonstandard operation during lining construction. The longer the service time, the greater the degree of structural deterioration; the longer the maintenance period and the greater the degree of lining defects, the more likely the lining structure is to be damaged and the higher the risk of lining demolition. (4) Construction method  
It mainly considers pretreatment measures, demolition location, demolition scope, demolition sequence, demolition means, lining reconstruction, monitoring, and measurement. The pretreatment measures include surrounding rock strengthening support and waterproof and drainage measures to ensure the stability of lining replacement surrounding rock and avoid mud and water inrush.