Study On Risk Management Of Rockfall Disaster At The Entrance Of Railway Tunnel In Mountainous Area

China has become the country with the largest scale and the highest speed of high-speed railway in the world.The main characteristics of our railway are large scale of road network,covering different climate and environmental conditions,and complex operation scene.In recent years,there have been a number of railway operation safety accidents caused by dangerous rock and rockfall disasters in mountainous areas,resulting in heavy losses of people’s lives and property,especially in the tunnel entrance section,and the consequences will be more serious once they happen.therefore,the safety prevention and control of railway tunnel portal operation in mountainous areas is very important.By identifying the risk factors of dangerous rock and rockfall disaster,the risk evaluation index system of dangerous rock and rockfall disaster at the entrance of railway tunnel in mountainous area is constructed,and the disaster grade of dangerous rock and rockfall is predicted and evaluated,so as to improve the prevention and control and response capacity of dangerous rock and rockfall disaster.This paper takes the mountain railway tunnel as the research background,the tunnel entrance dangerous rock fall disaster as the research object,on the basis of relevant literature review,consultation experts and field investigation,an index system suitable for risk assessment of dangerous rock and rockfall disaster at the entrance of mountain railway tunnel is constructed,and the risk assessment grade and evaluation index grade are divided.At the same time,through the comparison and selection of index weight theory and risk assessment model,the combined weighting method and unascertained measure theory(UMT)are introduced to improve the risk grade assessment model of G1-EWM-UMT dangerous rock and rockfall disaster,and the correctness and applicability of the model are verified by typical tunnel portal examples.finally,according to the risk grade,the prevention measures and suggestions of dangerous rock and rockfall disaster are put forward to achieve accurate prevention and effective control of dangerous rock and rockfall disaster.The main contents and research results of this paper are as follows:(1)the establishment of risk assessment index system of dangerous rock and rockfall disaster at the entrance of railway tunnel in mountainous area.The literature statistics method is selected to complete the classification and refinement of risk factors,and the fault tree analysis method is used to identify the main factors affecting the occurrence of dangerous rock and rockfall disasters,and a list of risk factors is compiled,including 44 risk factors.finally,according to the selection principle of evaluation index,the risk assessment index system of dangerous rock and rockfall disaster at the entrance of mountain railway tunnel is constructed,including 9 external risk indicators and 11 internal risk indicators.(2)the classification of risk assessment grade and index grade of dangerous rock and rockfall disaster at the entrance of railway tunnel in mountain area.With reference to the current national standards,technical regulations,relevant literature and expert experience,and comprehensively considering the occurrence probability and hazard grade of dangerous rock and rockfall disasters,the disaster grade of dangerous rock and rockfall is divided into four levels: high risk(grade Ⅳ),medium risk(grade Ⅲ),low risk(grade Ⅱ)and very low risk(grade Ⅰ).(3)the construction of risk assessment model of dangerous rock and rockfall disaster at the entrance of railway tunnel in mountainous area.Because the risk assessment of dangerous rock and rockfall disaster at the entrance of railway tunnel in mountainous area belongs to the typical problem of orderly segmentation,and the risk factors are complex,and the index information is unascertained and fuzzy,this paper chooses the unascertained measure theory as the risk assessment model,and introduces the improved G1 method,entropy weight method(EWM)and Lagrangian optimal multiplier method to weight the evaluation index combination.Finally,an improved G1-EWM-UMT risk assessment model of dangerous rock and rockfall is proposed.(4)Model verification based on engineering examples.Ten typical entrances and entrances of Yigong,Tongmai,Tongdu,Layue and Lulang tunnels on a railway line in southwest China are selected to verify the engineering examples to predict and evaluate the disaster grade of dangerous rock and rockfall.The results of risk assessment are as follows:Yigong entrance and exit section,Tongmai entrance and exit section,Tongdu exit section,Layue entrance section and Lulang tunnel exit section are all low grade(grade Ⅱ).The grade of rockfall disaster at the entrance of Tongdu tunnel and Lulang tunnel is medium(grade Ⅲ).According to the risk prediction results,the prevention and control plan of dangerous rock and rockfall disaster at the entrance of tunnel entrance is studied.