Research On Security Risk Assessment Methods Of Tunnel Construction And Operation Based On Index System

In the whole life cycle of tunnel engineering,the safety risk is the greatest in the construction and operation stages.In the construction stage,due to uncertain geological conditions and complicated construction procedures,safety accidents occur in tunnels,resulting in more serious consequences such as construction delay,cost overruns and even casualties.In the operation stage,tunnel structures often suffer from various degrees of diseases,which not only threaten the safety of tunnel pedestrians and traffic,but also shorten the service life of tunnel and cause tremendous troubles to tunnel maintenance units.Therefore,it is particularly important to carry out risk analysis,assessment and control of tunnel construction and operation safety.This paper relies on the research content of the sub-topic "hazard source identification and risk assessment of large and complex tunnels" in the national key research and development program "regional comprehensive transportation infrastructure security technology".Based on the theory of system safety,a safety risk assessment model of tunnel construction and in-service structure based on index system is constructed by combining the influence diagram method,BowTie method,expert investigation method,analytic hierarchy process(AHP),rough set theory(RS)and entropy weight method.In addition,this paper relying on under construction tunnel and built tunnel of extra-long highway tunnels in Chongqing and Shanxi,the application of safety risk assessment of extra-long highway tunnels and in-service structures is carried out.The main work and achievements of this paper are as follows:1)In order to better understand the conditions of accidents,this paper has carried out a lot of literature research and risk accident investigation and analysis.The main influencing factors of tunnel construction accidents and their relationship are analyzed by influence chart.At the operation stage,Bow Tie model is used to analyze the main causes,control measures and mitigation measures of structural safety accidents of existing tunnels.And the consequences,these are the important basis of the risk assessment method in this paper.2)Based on the investigation and analysis of tunnel construction accidents,the identification of external and internal risk sources of tunnel construction is carried out.According to the relevant norms and standards,literature and the investigation of construction units,the safety risk source grade evaluation criteria of tunnel construction stage are preliminarily divided.The index system of overall safety risk assessment before tunnel construction and the index system of tunnel construction safety risk assessment in typical geological section are established.3)The identification of structural safety risk events of in-service tunnels based on dangerous scenarios is carried out.The Bow Tie model is used to analyze the causes and consequences of typical risk events in existing tunnel structures.The external and internal risk sources of in-service tunnel structure safety are identified,and the safety risk index system of in-service tunnel structure is established.4)The safety risk assessment model of tunnel construction and in-service tunnel structure based on index system is established,and the determination method of index weight is emphatically studied.Through literature research and characteristics of safety factor index and risk factor index.The weighting coefficient of safety factor index(qualitative index)is determined by subjective and objective combination weighting method combined with analytic hierarchy process(AHP)and rough set theory(RS).The weight coefficient of risk factor index(quantitative index)is determined by analytic hierarchy process(AHP)and entropy theory.5)Applying the safety risk assessment model of tunnel construction and in-service structure proposed in this paper,a case study of the extra-long highway tunnels constructed and built in Chongqing,Shanxi and other places is carried out.The structural safety risk grade of extra-long highway tunnel construction and in-service tunnel is obtained,and appropriate risk control measures are taken to reduce the tunnel safety risk according to the evaluation results.According to the objectivity and subjectivity of risk sources,this paper systematically completes the identification of risk sources,forms a complete set of quantitative index system for safety evaluation of tunnel construction and in-service structures,and establishes an effective and practical risk evaluation model for tunnel safety.The evaluation method proposed in this paper provides direct support for risk prevention and control and safety improvement after evaluation,and provides a new idea for risk management and control of tunnel engineering.