Study On Safety Risk Assessment Of Construction Of High Geothermal Tunnel

In recent years,with China’s railway network continues to radiate to the northwest and southwest regions where the geothermal heat energy is more concentrated,a large number of high geothermal tunnels are bound to emerge in the process of railway construction.Due to the large buried depth and the influence of magmatic activity and underground hot water,high temperature surrounding rock,high temperature water vapor and other phenomena appear,resulting in the air temperature in the tunnel exceeding the temperature of safety warning line.Therefore,in such an environment,the superposition effect and uncertainty of various risk factors will increase significantly,which will promote the increase of accident rate.So it is very important and urgent to research the safety risk assessment of high geothermal tunnel construction.In order to control the construction safety risk of high geothermal tunnel more effectively,so as to reduce the incidence of accidents.Firstly,according to the existing relevant data of high geothermal tunnel,this paper analyzes and summarizes the causes of high geothermal tunnel,the particularity of construction safety,the mechanism of construction safety risk and the risk characteristics,and summarizes the commonly used methods of risk identification and risk evaluation.Ultimately,the paper selects WBS-RBS as the risk identification method,combines AHP,entropy model for group decision making,variable weight theory as the weighting method,and chooses cloud model as the evaluation method.Secondly,According to the statistical analysis results of high geothermal tunnel construction accidents,the WBS-RBS method is used to decompose the work structure and risk structure of high geothermal tunnel construction,and the WBS-RBS matrix is constructed.Through the 0-1 calibration of the matrix,the risk list is obtained.Then,through methods of questionnaire survey,22 risk factors are selected based on the contribution rate,independence and sensitivity of risk factors,and using them to construct the safety risk evaluation index system of high geothermal tunnel construction.Finally,entropy model for group decision making and AHP method are used to get the experts’ own weight and subjective weight respectively,and the constant weight matrix is obtained by fusing them.Then the variable weight of each index is obtained by using the variable weight theory through the constant weight and the state value of each index.Then,the cloud model is used to integrate the weight of each index with its state value,and the weighted cloud of each evaluation index is obtained.Then,the comprehensive membership degree is obtained and the comprehensive evaluation cloud drop diagram is simulated.Combined with the standard evaluation cloud,the safety risk of high geothermal tunnel construction is comprehensively evaluated.This paper takes Sangzhuling Tunnel of Lalin Railway as an example to verify and analyze the evaluation model.The final result shows that the safety risk level of sangzhuling tunnel construction is grade III,that is,the safety situation is medium to poor,which indicates that the factors that affect the success or failure of the project are still in an uncontrollable state,and the probability of accidents is high.By comparison,the evaluation results of this paper are basically consistent with the actual situation of the construction safety of Sangzhuling Tunnel.Through the comparison of the horizontal and vertical effects of the evaluation model,the objectivity,rationality and feasibility of the evaluation model are further verified.Finally,based on the construction safety evaluation results of Sangzhuling Tunnel,the main factors leading to the unsatisfactory evaluation results are analyzed and selected,such as the health status of operators,safety awareness of operators,high temperature resistance of blasting equipment,health management of on-site personnel,tunnel heat insulation and cooling,rock burst prevention and control,fault structure and fracture development,etc.,and specific control measures are provided.