Risk Assessment Method and Application for Tunnel Lining Demolition Construction

Abstract

The maintenance, reconstruction, and expansion of tunnels often require the removal of existing tunnel linings. However, there is a paucity of research on risk assessments during tunnel lining demolitions. In order to address this gap, we developed a risk assessment model for tunnel lining demolitions using a fuzzy hierarchy comprehensive evaluation and expert surveys. This model draws on on-site construction experience. A fuzzy hierarchy comprehensive evaluation assesses risk probability, while expert questionnaires evaluate risk loss. Our study applied this model to a tunnel project in Qinghai, determining that the overall risk level falls within category “V₃”, indicating acceptable risk. Nonetheless, ongoing vigilance and monitoring measures are necessary throughout the construction process. These findings contribute to a deeper understanding of tunnel lining demolition risk assessments for improving project management and safety.

1. Introduction

A tunnel is an important project created by humans in transportation construction, providing convenience for urban transportation and making significant contributions to people’s lives and economic development [1,2]. However, due to reasons such as maintenance, renovation, expansion, and structural insecurity [3,4,5], the dismantling of the lining of a tunnel has become an important task. By removing the lining, the tunnel structure can be repaired, reconstructed, and expanded to ensure the safe operation and traffic efficiency of the tunnel. At the same time, the removal of the lining can eliminate the potential safety problems of the tunnel structure [6,7].

A tunnel lining demolition is a complex problem involving many disciplines. At present, some pieces of research have been carried out on it [8]. In terms of the reasons for the demolition of a tunnel lining, studies have shown that aging [9,10], corrosion, cracks, and other problems of tunnel lining are the main reasons for the demolition. At the same time, the expansion and reconstruction of the tunnel’s structure, safety considerations, environmental protection, and other factors will also promote the demolition of the tunnel lining [11,12]. At present, mechanical demolitions and blasting demolitions are mainly used in the demolition of tunnel linings [13,14,15]. A mechanical demolition is to demolish the lining by using mechanical equipment such as a drilling machine, which has the advantages of a small impact on the surrounding environment and simple operation. A blasting demolition is the blasting decomposition of the lining by using explosives, which has the advantages of high efficiency and a wide application range [4]. In terms of the impact of a tunnel lining demolition, it mainly includes the impact on the tunnel structure, the impact on the surrounding environment, and the impact on transportation. The removal of a tunnel lining may have some impact on the tunnel’s structure, so detailed planning and design are required. At the same time, the demolition process may also have a certain impact on the surrounding environment and transportation, which requires effective control and management [16,17]. In general, the demolition of a tunnel lining is a complex and diverse problem, which requires in-depth discussion and research in theoretical research and practical application. The risks and challenges involved in the demolition of a tunnel lining cannot be ignored.

At present, there are relatively few studies on the risk of tunnel lining demolitions, and they mainly focus on the demolition methods and technologies. Existing studies have mainly focused on the comparison of demolition methods, as well as the structural deformation, environmental pollution, and other issues that may be involved in the demolition process. However, the research on risk assessments in the process of tunnel lining demolitions is still relatively insufficient. The purpose of this paper is to conduct in-depth research and a discussion on the risks of tunnel lining demolitions and to comprehensively understand the potential risks and challenges in the demolition process. The corresponding risk assessment method is proposed to ensure the safety and smooth progress of tunnel lining demolitions. The research of this paper will provide theoretical support and practical guidance for the demolition of tunnel linings and provide a useful reference point for urban traffic construction and tunnel maintenance.

2. Risk Index Framework for Tunnel Lining Demolition Construction

2.1. Construction Principles of Risk Indicators

The purpose of establishing the risk evaluation index system of tunnel lining demolition construction is to analyze the risk factors existing in the process of tunnel lining demolition construction and to measure the overall risk of tunnel lining demolition construction. Therefore, the index system must scientifically, objectively, reasonably, and comprehensively reflect all factors affecting the safety of tunnel lining demolition construction [18,19]. However, it is very difficult to establish a set of scientific and reasonable risk evaluation index systems. Therefore, it is necessary to analyze and judge according to certain principles in order to better solve this problem.

(1) Systematic principle

Tunnel lining demolition construction is a huge and complex man-machine system related to engineering geological conditions and production and construction organization. To evaluate its risk and establish the risk evaluation index system, we need to think about it with the idea of system engineering so that the index can reflect the factors affecting the risk of tunnel lining demolition construction as comprehensively as possible [20].

(2) Scientific principle

The construction of a risk evaluation index system for tunnel lining demolition construction must conform to the actual situation of tunnel lining demolition construction, based on the actual characteristics of the project and scientific theory, so as to ensure the objectivity and reliability of the index system [21].

(3) Conciseness principle

The construction of the risk evaluation index system of tunnel lining demolition construction should be based on the comprehensive and systematic analysis of various potential risk factors during the construction period, and the main risk factors affecting the safety of high-rise lining demolition construction should be determined as the research object of risk evaluation, so as to ensure the key control of those risk factors with high frequency and serious consequences.

(4) Independence principle

Any indicator system is composed of a certain number of indicators. Each indicator should not only have clear content but also be relatively independent. The indicators at the same level do not overlap each other, and there is no inclusion or intersection between them [22].

(5) Universality principle

A set of scientific and reasonable index systems should be able to reflect the situation of the whole industry. At the same time, through appropriate transformation, the risk assessment of different tunnel lining demolition construction can be carried out [23,24].

(6) Combination of qualitative and quantitative principles

The construction of the index system should meet the principle of combining qualitative and quantitative analysis; that is, on the basis of qualitative analysis, quantitative treatment should be carried out. Only through quantification can we accurately reflect the risk of lining demolition construction. The risk assessment of road lining demolition construction is advanced, which studies the possibility of risk occurrence and the possible loss. The quantitative analysis of this problem mainly relies on the statistical data of similar risks in the past. For qualitative indicators lacking statistical data, the scoring method can be used to approximate the quantification by using expert opinions [25].

(7) Feasibility principle

The selection of evaluation indexes should be practical and operable. It is necessary to consider that the evaluation index system can be implemented under realistic conditions. The data required for obtaining the index value should be easy to investigate and collect, and the index should be easy to understand and calculate so as to ensure the smooth progress of the evaluation work [26].

2.2. 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 demolished 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. The demolition positions include the demolition of the lining vault, arch waist, side wall, and full section demolition. The demolition risks at different positions must be different, and it is easy to see that the risk of full-section demolition is higher. The demolition scope is divided into circumferential angle and longitudinal distance, and the size of the demolition scope directly affects the construction difficulty and progress. The demolition sequence mainly includes longitudinal and circumferential aspects. The disturbance and damage to the existing lining structure caused by demolition do not match the degree of damage it can withstand, which will cause disturbance and collapse of the UN demolished parts in the demolition operation. A demolition refers to the demolition methods of the lining structure, including blasting, mechanical, and manual methods. Different methods have different demolition efficiency and risks. Lining reconstruction includes the timing of lining reconstruction, whether the lining is plain concrete or reinforced concrete, and whether the lining is strengthened. Lining reconstruction directly determines the safety of the tunnel lining demolition process. During the lining removal process, monitoring and measurement are used as auxiliary means to measure the stress and deformation of the lining structure in the non-operation area so as to ensure the safety of the demolition in the operation area.

(5) Construction organization

Management, equipment, construction personnel level, emergency measures, and other measures are mainly considered. The organization ability and mobilization ability of the project tunnel lining demolition construction management team and the team with high management level can overcome the difficulties in construction, solve the risk events, and ensure the construction progress [32]. Equipment mainly refers to the removal of trolleys and large mechanized equipment, one of which ensures the construction speed, and the other ensures the construction safety. The level of construction personnel refers to the equipment operation proficiency, technical level, and lining removal experience of on-site construction personnel, especially whether they have removal experience, which greatly affects the smooth implementation of lining removal construction. Emergency measures refer to taking timely and appropriate measures to ensure the safety of demolition construction in case of a large-scale collapse of lining, falling blocks of adjacent lining concrete, mud and water inrush, etc.

(6) Method for determining risk indicators

In order to further determine the risk events and risk factors of tunnel lining demolition construction, a questionnaire was sent to experts in the industry to obtain more practical results. Through two rounds of questionnaires (see Appendix A for details), the following 65 valid data were obtained, including 23 valid data in the first round and 42 valid data in the second round. Through the first round of questionnaires, the results are shown in Figure 1. It is concluded that the risk events of tunnel lining demolition construction mainly include adjacent lining cracks, accidental lining falling or collapse, surrounding rock collapse and affecting the operation of adjacent lines. Among them, the cracking of adjacent lining refers to the damage to adjacent structures caused by lining removal. Accidental falling or collapse of the lining refers to the accidental falling of the lining during the removal process, resulting in personal injury and equipment damage. Surrounding rock collapse refers to the collapse of surrounding rock during lining removal, resulting in casualties, equipment damage, and cost increases. The impact on the operation of adjacent lines refers to the damage to the structure and equipment of adjacent lines caused by the removal of lining and the failure of normal operation. Through the second round of questionnaires, the risk factors corresponding to the possible risk events in the tunnel lining demolition construction are obtained, as shown in Figure 2, Figure 3, Figure 4 and Figure 5. After comprehensive analysis, the tunnel lining demolition indicators are shown in Figure 6.

3. Risk Assessment Method of Tunnel Lining Demolition Construction

3.1. Fuzzy Comprehensive Evaluation Method and Process

A model is a practical generalization, and a practical model can only abstract a conceptual model that reflects the actual change process from the actual system after having a deep understanding of the composition, structure, and other aspects of the studied system and mastering a large amount of actual information, data, and change patterns [33]. The fuzzy comprehensive evaluation method applies the principle of fuzzy transformation and the basic theory of fuzzy mathematics—membership degree or membership function—to describe the fuzzy information quantity of intermediate transitions, considers various factors related to the evaluation of things, floating selection factor thresholds, makes reasonable division, and then uses traditional mathematical methods to process, in order to scientifically draw evaluation conclusions [34]. The fuzzy evaluation method can provide specific mathematical models that are simple and easy to master. It is a good method for evaluating complex problems with multiple factors and levels and has wide applicability. Due to the need to combine many quantitative and qualitative uncertainty indicators in the risk assessment of local demolition of tunnel lining construction, the fuzzy comprehensive evaluation method gives sufficient attention to uncertain factors and can make a comprehensive evaluation of things determined by multiple factors. Based on this objective fact and the comparison of the above evaluation methods, this article adopts the fuzzy comprehensive evaluation method for adaptability evaluation.

The basic idea of the fuzzy comprehensive evaluation method is to decompose the influencing factors based on the evaluation objectives, construct different levels of indicator systems, assign values to these indicators and determine weights, and finally use the evaluation model to calculate the evaluation values, which are then sorted and evaluated [35,36]. On the basis of determining the evaluation criteria and weights of evaluation factors and factors, the principle of fuzzy set transformation is applied to describe the fuzzy boundaries of each factor and factor using membership degree. A fuzzy evaluation matrix is constructed, and the reliability of the evaluation object is determined through composite operations [37]. The specific process is shown in Figure 7.

3.2. Weight Analysis of Risk Assessment Indicators

(1) Analytic Hierarchy Process

Analytic Hierarchy Process (AHP) is a decision analysis method that decomposes the decision-making problem into different levels of structure, including the target layer, the criterion layer, and the scheme layer. This method is mainly to quantitatively describe the subjective judgment of people so as to make qualitative and quantitative analyses of decision-making problems [38]. The essence of the AHP method is a kind of thinking method. It makes full use of people‘s analyses, judgment, and comprehensive abilities to hierarchical decision-making problems, so as to facilitate decision-making on complex problems. In practical applications, the AHP method usually includes the following steps [39]:

(a) Establish a hierarchical structure: decompose the decision-making problem according to the overall goal, sub-goal, evaluation criteria, and alternative levels.

(b) Construct a pairwise comparison judgment matrix: For each level, it is necessary to construct a pairwise comparison judgment matrix to represent the relative importance of each element.

(c) Calculate the weight vector: By solving the eigenvector of the judgment matrix, the priority weight of each level element to a certain element at the previous level is obtained.

(d) Hierarchical total sorting: According to the weight vector, the hierarchical total sorting is carried out to obtain the weight of each level element to the total target.

(e) Application examples: The analytic hierarchy process is applied to specific problems, each index is compared in pairs, the judgment matrix is constructed, and the relative advantages and disadvantages of each evaluation index are calculated.

Through the above steps, the analytic hierarchy process can help decision-makers analyze complex problems systematically so as to make more scientific and reasonable decisions.

(2) Weight analysis

Through the preliminary selection of risk assessment indicators for local demolition of tunnel lining construction, it can be seen that there are many evaluation indicators, and the system is too large. If all indicators are selected, it is likely to have a negative impact on the comprehensive evaluation, making the evaluation results meaningless [40]. According to the principle of establishing an indicator system, when selecting evaluation indicators, they should be representative and reflect the essence of the evaluation problem. Therefore, in order to ensure the objectivity of the evaluation, it is necessary to screen the evaluation indicators, distinguish between primary and secondary, and form a reasonable and feasible evaluation indicator system.

Due to the large number of risk assessment indicators for local demolition of tunnel lining construction, some indicators have significant correlations, and some data collection is difficult. In order to reflect the importance of each evaluation indicator in the evaluation system, this article uses the analytic hierarchy process to determine the weight of the indicators and screens the indicators based on the size of the weight. Removing some indicators with relatively small weights is not only beneficial for simplifying decision-making problems but also avoids errors in judgment caused by too many indicators [41].

Analytic Hierarchy Process (AHP) was used to calculate the weights of four influencing factors: adjacent lining cracking, accidental lining falling or collapse, surrounding rock collapse, and the impact on the operation of adjacent lines. The specific results are shown in

Table 1. Weighting analysis of risk assessment for partial demolition of tunnel lining construction.

A	B1	B2	B3	B4
B1	1	1/5	1/4	3
B2	5	1	1	4
B3	4	1	1	5
B4	1/3	1/4	1/5	1
weight	0.1238	0.4093	0.3965	0.0704
sequence	1	1/5	1/4	3
λmax = 4.168; CI = 0.056; CR = 0.0629

,

Table 2. Weight analysis of adjacent lining crack damage indicators.

B1	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19
C1	1	3	2	1/3	4	1/5	1/4	1/2	1	1/2	2	1/6	5	1	7	6	4	8	9
C2	1/3	1	1/2	1/9	2	1/9	1/9	1/6	1/3	1/6	1	1/9	2	1/3	2	2	1	3	3
C3	1/2	2	1	1/6	2	1/9	1/8	1/4	1/2	1/4	1	1/9	3	1/2	4	3	2	4	5
C4	3	9	6	1	9	1/2	1/2	2	3	2	6	1/2	9	3	9	9	9	9	9
C5	1/4	1/2	1/2	1/9	1	1/9	1/9	1/8	1/4	1/8	1/2	1/9	1	1/4	2	2	1	2	2
C6	5	9	9	2	9	1	1	2	5	3	9	1	9	5	9	9	9	9	9
C7	4	9	8	2	9	1	1	2	4	2	8	1	9	4	9	9	9	9	9
C8	2	6	4	1/2	8	1/2	1/2	1	2	1	4	1/3	9	2	9	9	8	9	9
C9	1	3	2	1/3	4	1/5	1/4	1/2	1	1/2	2	1/6	5	1	7	6	4	8	9
C10	2	6	4	1/2	8	1/3	1/2	1	2	1	4	1/3	9	2	9	9	8	9	9
C11	1/2	1	1	1/6	2	1/9	1/8	1/4	1/2	1/4	1	1/9	2	1/2	3	3	2	4	4
C12	6	9	9	2	9	1	1	3	6	3	9	1	9	6	9	9	9	9	9
C13	1/5	1/2	1/3	1/9	1	1/9	1/9	1/9	1/5	1/9	1/2	1/9	1	1/5	7	1	1	2	1
C14	1	3	2	1/3	4	1/5	1/4	1/2	1	1/2	2	1/6	5	1	7	6	4	8	9
C15	1/7	1/2	1/4	1/9	1/2	1/9	1/9	1/9	1/7	1/9	1/3	1/9	1/7	1/7	1	1	1/2	1	1
C16	1/6	1/2	1/3	1/9	1/2	1/9	1/9	1/9	1/6	1/9	1/3	1/9	1	1/6	1	1	1/2	1	2
C17	1/4	1	1/2	1/9	1	1/9	1/9	1/8	1/4	1/8	1/2	1/9	1	1/4	2	2	1	2	2
C18	1/8	1/3	1/4	1/9	1/2	1/9	1/9	1/9	1/8	1/9	1/4	1/9	1/2	1/8	1	1	1/2	1	1
C19	1/9	1/3	1/5	1/9	1/2	1/9	1/9	1/9	1/9	1/9	1/4	1/9	1	1/9	1	1/2	1/2	1	1
weight	0.0464	0.017	0.0247	0.1092	0.013	0.1508	0.1375	0.0816	0.0464	0.0803	0.0223	0.1619	0.0135	0.0464	0.0086	0.0099	0.0134	0.0085	0.0084
λmax = 20.0434; CI = 0.058; CR = 0.0358

,

Table 3. Analysis of the weight of lining accidental falling or collapse indicators.

B2	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19
C1	1	1/2	1	1/8	1/5	1/9	1/6	2	1/3	1/4	1/2	1/8	1	1/2	1/2	1/2	1/3	1/3	1
C2	2	1	2	1/4	1/3	1/5	1/3	4	1/2	1/2	1	1/4	2	1	1	1	1/2	1/2	2
C3	1	1/2	1	1/8	1/5	1/9	1/6	2	1/3	1/4	1/2	1/8	1	1/2	1/2	1/2	1/3	1/3	1
C4	8	4	8	1	2	1/2	2	9	3	2	4	1	8	4	4	4	3	3	8
C5	5	3	5	1/2	1	1/2	2	9	2	2	3	1/2	5	3	3	3	2	2	5
C6	9	5	9	2	2	1	2	9	3	3	5	1/2	9	5	5	5	3	3	9
C7	6	3	6	1/2	1/2	1/2	1	9	2	2	3	1/2	6	3	3	3	2	2	6
C8	1/2	1/4	1/2	1/9	1/9	1/9	1/9	1	1/6	1/8	1/4	1/9	1/2	1/4	1/4	1/4	1/6	1/6	1/2
C9	3	2	3	1/3	1/2	1/3	1/2	6	1	1/2	2	1/2	3	2	2	2	1	1	3
C10	4	2	4	1/2	1/2	1/3	1/2	8	2	1	2	1/2	3	2	2	2	1	1	3
C11	2	1	2	1/4	1/3	1/5	1/3	4	1/2	1/2	1	1/4	2	1	1	1	1/2	1/2	2
C12	8	4	8	1	2	2	2	9	2	2	4	1	8	4	4	4	3	3	8
C13	1	1/2	1	1/8	1/5	1/9	1/6	2	1/3	1/3	1/2	1/8	1	1/2	1/2	1/2	1/3	1/3	1
C14	2	1	2	1/4	1/3	1/5	1/3	4	1/2	1/2	1	1/4	2	1	1	1	1/2	1/2	2
C15	2	1	2	1/4	1/3	1/5	1/3	4	1/2	1/2	1	1/4	2	1	1	1	1/2	1/2	2
C16	2	1	2	1/4	1/3	1/5	1/3	4	1/2	1/2	1	1/4	2	1	1	1	1/2	1/2	2
C17	3	2	3	1/3	1/2	1/3	1/2	6	1	1	2	1/3	3	2	2	2	1	1	3
C18	3	2	3	1/3	1/2	1/3	1/2	6	1	1	2	1/3	3	2	2	2	1	1	3
C19	1	1/2	1	1/8	1/5	1/9	1/6	2	1/3	1/3	1/2	1/8	1	1/2	1/2	1/2	1/3	1/3	1
weight	0.0154	0.0291	0.0154	0.1247	0.0884	0.1453	0.0849	0.009	0.0495	0.0572	0.0291	0.1335	0.0157	0.0291	0.0291	0.0291	0.0498	0.0498	0.0157
λmax = 19.2492; CI = 0.0138; CR = 0.0085

,

Table 4. Weight Analysis of Surrounding Rock Collapse Index.

B3	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19
C1	1	5	4	9	5	5	1/3	1/2	1/2	1	3	2	8	3	9	8	5	8	9
C2	1/5	1	1	2	1	1	1/9	1/9	1/9	1/5	1/2	1/3	2	1/2	2	2	1	2	2
C3	1/4	1	1	2	1	2	1/9	1/8	1/7	1/4	1	1/2	2	1	2	2	1	2	2
C4	1/9	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/9	1/3	1/4	1	1/3	1	1	1/2	1	1
C5	1/5	1	1	2	1	1	1/9	1/9	1/9	1/5	1/2	1/3	2	1/2	2	2	1	2	2
C6	1/5	1	1/2	2	1	1	1/9	1/9	1/9	1/5	1/2	1/5	2	1/2	2	2	1	2	2
C7	3	9	9	9	9	9	1	2	2	3	9	6	9	9	9	9	9	9	9
C8	2	9	8	9	9	9	1/2	1	1	2	6	4	9	6	9	9	9	9	9
C9	2	9	7	9	9	9	1/2	1	1	2	6	4	9	6	9	9	9	9	9
C10	1	5	4	9	5	5	1/3	1/2	1/2	1	3	2	8	3	9	8	5	8	9
C11	1/3	2	1	3	2	2	1/9	1/6	1/6	1/3	1	1/2	3	1	3	2	2	3	3
C12	1/2	3	2	4	3	5	1/6	1/4	1/4	1/2	2	1	4	2	5	4	3	4	5
C13	1/8	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/8	1/3	1/4	1	1/2	1	1	1/2	1	1
C14	1/3	2	1	3	2	2	1/9	1/6	1/6	1/3	1	1/2	2	1	3	3	2	2	3
C15	1/9	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/9	1/3	1/5	1	1/3	1	1	1/2	1	1
C16	1/8	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/8	1/2	1/4	1	1/3	1	1	1/2	1	1
C17	1/5	1	1	2	1	1	1/9	1/9	1/9	1/5	1/2	1/3	2	1/2	2	2	1	2	3
C18	1/8	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/8	1/3	1/4	1	1/2	1	1	1/2	1	1
C19	1/9	1/2	1/2	1	1/2	1/2	1/9	1/9	1/9	1/9	1/3	1/5	1	1/3	1	1	1/3	1	1
weight	0.0955	0.0206	0.0246	0.0124	0.0206	0.0196	0.2018	0.1543	0.153	0.0955	0.0324	0.0538	0.0128	0.0317	0.0123	0.0128	0.0213	0.0128	0.0121
λmax = 19.4613; CI = 0.0256; CR = 0.0158

and

Table 5. Weight analysis of indicators affecting the operation of adjacent lines.

B4	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19
C1	1	1	2	3	4	1/2	1/4	1/3	3	2	1	1	4	2	5	6	3	2	1/3
C2	1	1	2	3	4	1/2	1/4	1/3	3	2	1	1	4	2	5	6	3	2	1/3
C3	1/2	1/2	1	2	3	1/5	1/8	1/6	2	1	1/2	1	2	1	3	4	2	1	1/7
C4	1/3	1/3	1/2	1	2	1/4	1/8	1/6	1	1/2	1/3	1/2	2	1	2	3	2	1	1/8
C5	1/4	1/4	1/3	1/2	1	1/7	1/9	1/8	1/2	1	1/4	1/3	1	1/2	1	2	1	1/2	1/7
C6	2	2	5	4	7	1	1/2	1	6	4	2	2	8	4	8	9	6	4	1/3
C7	4	4	8	8	9	2	1	1	9	8	4	5	8	6	8	9	6	4	1
C8	3	3	6	6	8	1	1	1	9	7	8	5	8	5	7	8	9	6	1/2
C9	1/3	1/3	1/2	1	2	1/6	1/9	1/9	1	1	1	1/2	1	1/2	1	3	1	1/2	1/7
C10	1/2	1/2	1	2	1	1/4	1/8	1/7	1	1	1	1/2	1	1/2	2	2	1	1/2	1/6
C11	1	1	2	3	4	1/2	1/4	1/8	1	1	1	1/2	1	1/2	1	3	3	1/2	1/9
C12	1	1	1	2	3	1/2	1/5	1/5	2	2	2	1	2	1	3	5	2	1	1/9
C13	1/4	1/4	1/2	1/2	1	1/8	1/8	1/8	1	1	1	1/2	1	1/2	2	1	1	1	1/8
C14	1/2	1/2	1	1	2	1/4	1/6	1/5	2	2	2	1	2	1	3	3	2	1	1/7
C15	1/5	1/5	1/3	1/2	1	1/8	1/8	1/7	1	1/2	1	1/3	1/2	1/3	1	2	1/2	1/3	1/9
C16	1/6	1/6	1/4	1/3	1/2	1/9	1/9	1/8	1/3	1/2	1/3	1/5	1	1/3	1/2	1	1/2	1/3	1/6
C17	1/3	1/3	1/2	1/2	1	1/6	1/6	1/9	1	1	1/3	1/2	1	1/2	2	2	1	1/2	1/8
C18	1/2	1/2	1	1	2	1/4	1/4	1/6	2	2	2	1	1	1	3	3	2	1	1/9
C19	3	3	7	8	7	3	1	2	7	6	9	9	8	7	9	6	8	9	1
weight	0.0531	0.0531	0.0302	0.0227	0.0149	0.101	0.1573	0.1447	0.0195	0.0227	0.0335	0.0391	0.018	0.0323	0.0142	0.0111	0.0175	0.0315	0.1836
λmax = 19.9517; CI = 0.0529; CR = 0.0326

.

According to the single ranking of each level, the total ranking of the weights of the levels is calculated, and the specific results are shown in

Table 6. Overall ranking of indicator weights.

	B1	B2	B3	B4	Total Ranking Weight	Total Ranking
	0.1238	0.4093	0.3965	0.0704
C1	0.0464	0.0154	0.0955	0.0531	0.0537	8
C2	0.017	0.0291	0.0206	0.0531	0.0259	14
C3	0.0247	0.0154	0.0246	0.0302	0.0212	16
C4	0.1092	0.1247	0.0124	0.0227	0.0711	7
C5	0.013	0.0884	0.0206	0.0149	0.0470	9
C6	0.1508	0.1453	0.0196	0.101	0.0930	3
C7	0.1375	0.0849	0.2018	0.1573	0.1429	1
C8	0.0816	0.009	0.1543	0.1447	0.0852	5
C9	0.0464	0.0495	0.153	0.0195	0.0880	4
C10	0.0803	0.0572	0.0955	0.0227	0.0728	6
C11	0.0223	0.0291	0.0324	0.0335	0.0299	12
C12	0.1619	0.1335	0.0538	0.0391	0.0988	2
C13	0.0135	0.0157	0.0128	0.018	0.0144	19
C14	0.0464	0.0291	0.0317	0.0323	0.0325	10
C15	0.0086	0.0291	0.0123	0.0142	0.0189	18
C16	0.0099	0.0291	0.0128	0.0111	0.0190	17
C17	0.0134	0.0498	0.0213	0.0175	0.0317	11
C18	0.0085	0.0498	0.0128	0.0315	0.0287	13
C19	0.0084	0.0157	0.0121	0.1836	0.0252	15

.

The total sorting consistency ratio of layer C is

$$\mathrm{C}\mathrm{R}=0.0358+0.0085+0.0158+0.0326=0.0927<0.1$$

(1)

Therefore, the overall consistency test of the hierarchy indicates that the sorting has good consistency. Based on the total hierarchical ranking weights of the above hierarchical structure model, we can determine the weight order of the 19 influencing factors for the risk assessment of local demolition of tunnel lining construction: 1—pretreatment measures; 2—demolition methods; 3—existing lining technical conditions; 4—demolition location; 5—unfavorable geology; 6—demolition scope; 7—existing lining structure; 8—surrounding rock state; 9—lining section; 10—monitoring measurement; 11—construction personnel level; 12—demolition sequence; 13—emergency rescue; 14—groundwater; 15—condition of adjacent line equipment; 16—ground stress; 17—construction machinery and equipment; 18—construction organization management; 19—reconstruction lining quality.

3.3. Classification of Risk Levels

Firstly, based on the characteristics of tunnel stability issues and the understanding of general risk concepts, and based on two methods: construction stability reliability risk and construction stability risk consequence; the stability risk of a local demolition of the tunnel lining and the risk factors of each layer are graded, and then risk assessment is carried out. The risk level of construction stability and reliability is divided as shown in

Table 7. Risk level of construction stability and reliability.

Probability Level	Probability Range	Center Value	Probability Level Description
Level 1	<0.0003	0.0001	Very unlikely
Level 2	0.0003~0.003	0.001	Impossibly
Level 3	0.003~0.03	0.01	Accidentally
Level 4	0.03~0.3	0.1	Possibly
Level 5	>0.3	1	Likely

.

The consequence level of construction stability risk is divided as shown in

Table 8. Consequence level of construction stability.

Level	Level 1	Level 2	Level 3	Level 4	Level 5
Description	Mild	Larger	Severe	Very serious	Catastrophic

.

The risk classification criteria are obtained by comprehensively considering the probability and consequences of risk, as shown in

Table 9. Risk grading evaluation standards.

Risk Level	Acceptance Criteria	Treatment Measures
Level 1	Negligible	The risk is small, and risk treatment measures and monitoring are not needed.
Level 2	Permissible	Risk second, need to pay attention to, routine management.
Level 3	Acceptable	Attention should be paid to take measures to monitor.
Level 4	Not expected (Partially unacceptable)	The risk is high, and risk treatment measures must be taken to reduce the risk and strengthen the monitoring, and the cost of meeting the risk reduction is not higher than the loss after the risk occurs.
Level 5	Unacceptable	Risk is the biggest; we must attach great importance to and avoid it; otherwise, we should at least reduce the risk to the unexpected level at any cost.

.

Due to the rough nature of dividing the risk into five levels, it is necessary to determine more detailed grading results through quantification. Therefore, a percentage-based scoring method is adopted, and the corresponding scoring values for each level are defined in

Table 10. Quantitative grading.

Risk Level	V1	V2	V3	V4	V5
Grading value	4 ≤ Q < 5	3 ≤ Q < 4	2 ≤ Q < 3	1 ≤ Q < 2	0 < Q ≤ 1

.

We invite experts in related fields to determine the relationship between the evaluation index and the evaluation set so as to evaluate each evaluation index qualitatively and quantitatively and finally determine its reasonable weight to improve the objectivity and accuracy of the results.

When considering a specific evaluation index C_j, if there are multiple evaluation opinions, where V₁ comments are n₁, V₂ comments are n₂, V₃ comments are n₃, V₄ comments are n₄, and V₅ comments are n₅, then we can construct the membership vector of the evaluation opinion set V:

$${\mathrm{r}}_{\mathrm{j}}=\left(\frac{{\mathrm{n}}_1}{\mathrm{n}}\frac{{\mathrm{n}}_2}{\mathrm{n}}\frac{{\mathrm{n}}_3}{\mathrm{n}}\frac{{\mathrm{n}}_4}{\mathrm{n}}\frac{{\mathrm{n}}_5}{\mathrm{n}}\right)$$

(2)

The membership vectors of each evaluation index are calculated by appropriate mathematical formulas, and they are summarized to obtain the evaluation matrix related to each factor.

We use the weighted average method to construct a fuzzy comprehensive evaluation model. By multiplying the evaluation matrix R of each factor with its corresponding weight vector W, the evaluation vector C is obtained.

$$\mathrm{C}=\mathrm{W}\times \mathrm{R}$$

(3)

Finally, we calculate with the evaluation level set V to obtain the final comprehensive score v.

$$\mathrm{v}=\mathrm{C}\times {\mathrm{V}}^{\mathrm{T}}$$

(4)

4. Engineering Application

4.1. Project Overview

The starting and ending mileage of a certain tunnel in Qinghai is DK275 + 588~DK277 + 868, with a total length of 2280 m. It is a double-track highway tunnel. The 81 m lining type of tunnel DK277 + 455~DK277 + 536 section is V_c-2, and the 4 m lining type of tunnel DK277 + 536~DK277 + 540 section is V_b-2. The main strata crossed by the tunnel are sandstone, shale, and mudstone, and the groundwater is mainly phreatic water and bedrock fissure water. According to an on-site investigation, the blasting demolition of the secondary lining inside the tunnel was carried out on three sections of reinforced concrete lining. The controlled blasting technology of “collapse + cutting” is adopted for blasting demolition. Using a self-made protective trolley, two layers of waste tires are laid on the top of the trolley and directly below the explosion zone before detonation, and a layer of waste tires is hung on the side of the trolley to prevent flying stones and falling debris from directly impacting the trolley. The secondary lining of the tunnel will be demolished in zones, and the demolition plan is shown in Figure 8 and Figure 9. After blasting the secondary lining concrete, it is necessary to reinforce the initial support. This section of the tunnel is shallowly buried, rich in water, and has expansive properties. After blasting a plate of 6 m, the original initial support must be treated with grouting to stop water. After grouting is completed, double-layer waterproof boards will be hung again, and the circumferential drainage blind pipe will be densified to 2 m per layer.

4.2. Risk Evaluation

Firstly, invite 10 industry experts to statistically process the scoring data and construct a fuzzy subset to obtain the membership vectors of each single factor in the indicator layer. Then, integrate all the single-factor membership vectors to construct a fuzzy comprehensive evaluation membership matrix R:

$$\mathrm{R}=\left(\begin{array}{c}{\mathrm{r}}_1\\ {\mathrm{r}}_2\\ {\mathrm{r}}_3\\ {\mathrm{r}}_4\\ {\mathrm{r}}_5\\ {\mathrm{r}}_6\\ {\mathrm{r}}_7\\ {\mathrm{r}}_8\\ {\mathrm{r}}_9\\ {\mathrm{r}}_{10}\\ {\mathrm{r}}_{11}\\ {\mathrm{r}}_{12}\\ {\mathrm{r}}_{13}\\ {\mathrm{r}}_{14}\\ {\mathrm{r}}_{15}\\ {\mathrm{r}}_{16}\\ {\mathrm{r}}_{17}\\ {\mathrm{r}}_{18}\\ {\mathrm{r}}_{19}\end{array}\right)=\left(\begin{array}{ccccc}0.4& 0.3& 0.2& 0.1& 0\\ 0.1& 0.2& 0.5& 0.1& 0.1\\ 0& 0.1& 0.3& 0.5& 0.2\\ 0& 0& 0.2& 0.5& 0.3\\ 0& 0& 0.1& 0.7& 0.2\\ 0.1& 0.2& 0.5& 0.2& 0.1\\ 0& 0.1& 0.1& 0.2& 0.6\\ 0.1& 0.1& 0& 0.2& 0.6\\ 0& 0& 0& 0.2& 0.8\\ 0.3& 0.5& 0.2& 0& 0\\ 0.1& 0.2& 0.2& 0.3& 0.2\\ 0.2& 0.3& 0.3& 0.1& 0.1\\ 0& 0& 0& 0.1& 0.9\\ 0& 0.1& 0.3& 0.2& 0.3\\ 0.1& 0.1& 0.2& 0.3& 0.4\\ 0& 0& 0.1& 0.1& 0.8\\ 0.1& 0.1& 0.1& 0.2& 0.5\\ 0.1& 0.1& 0.1& 0.3& 0.4\\ 0& 0& 0& 0& 1\end{array}\right)$$

(5)

Using the weighted average method to construct a fuzzy comprehensive evaluation model, the evaluation matrix R and its corresponding weight vector W are used to calculate the matrix, and the evaluation vector C is obtained:

$$\begin{gathered} \mathrm{W}=(0.5370 0.0259 0.2120 0.0711 0.0470 0.0930 0.1429 0.0852 \\ 0.0880 0.0728 0.0299 0.0988 0.0144 0.0325 0.0189 0.0317 0.0287 0.0252) \end{gathered}$$

(6)

$$\mathrm{C}=(0.0944 0.0148 0.1814 0.2181 0.3693)$$

(7)

Finally, calculate with the comment level set vector V to obtain the final comprehensive rating value.

$$\mathrm{v}=\left(0.2403 0.2651 0.3363 0.1340 0.1007\right)\times {\left(5 4 3 2 1\right)}^{\mathrm{T}}=2.4138$$

(8)

Based on the above evaluation results, the risk level of local demolition construction of the tunnel lining is V₃, indicating that the risk of local demolition construction of the tunnel lining is within an acceptable range. However, the risks of tunnel construction still need to be taken seriously, and further measures should be taken to minimize safety hazards and ensure construction safety. The evaluation results are consistent with the risk assessment results of tunnel lining demolition carried out by experts organized by the design unit and construction unit. No construction accidents occurred during the tunnel construction process, verifying the rationality of the evaluation method.

5. Conclusions

This article takes the risk assessment of local demolition construction of tunnel lining as the research object and explores the safety risk assessment and its application to local demolition construction of tunnel lining. We mainly studied the risk influencing factors, risk assessment index system, risk assessment model, and evaluation criteria for local demolition construction of tunnel lining. Finally, we applied the research results to a certain tunnel in Qinghai for risk assessment of local demolition construction of tunnel lining. The main achievements are as follows:

(1) The dismantling and replacement of tunnel lining is one of the important measures to solve the hazards existing in tunnel construction. Currently, there is no clear and systematic mechanism research, and most of them rely on empirical design and construction. During the local demolition construction process of a tunnel lining, it is difficult and risky. Due to the complexity and uncertainty of tunnel lining demolition construction, the geological conditions of tunnel lining demolition construction are complex, the engineering strength is high, the construction organization is difficult, and there are many construction risks. Ensuring construction safety is the key and difficult point.

(2) A risk assessment model for tunnel lining demolition construction is established based on fuzzy hierarchical comprehensive evaluation and expert survey. The fuzzy hierarchical comprehensive evaluation method is used to evaluate the probability level of tunnel lining demolition construction risk, and an expert questionnaire survey is used to evaluate the risk loss level of tunnel lining demolition construction.

(3) Applying research results to carry out risk assessment of lining demolition construction in a certain tunnel in Qinghai, it was found that the overall risk level of lining demolition construction in a certain tunnel in Qinghai belongs to “V₃”. The evaluation results are consistent with the risk assessment results of tunnel lining demolition carried out by experts organized by the design unit and construction unit. No construction accidents occurred during the tunnel construction process, verifying the rationality of the evaluation method. At the same time, it provides a reference for the application of risk assessment and control technology in tunnel lining demolition construction in practical engineering.

(4) The risk assessment model for tunnel lining demolition construction facilitates risk mitigation, decision optimization, resource allocation efficiency, and enhanced safety. Through quantitative analysis and comprehensive evaluation, this assessment tool provides reliable data support to ensure the smooth implementation and successful completion of tunnel lining demolition projects.