Study On Application Of Rock Burst And Large Deformation Risk Assessment In The Construction Of High Ground Stress Tunnels

In recent years,with the rapid development of infrastructure construction in China,the scale of tunnel and underground engineering has also increased rapidly,and most of them are concentrated in the western regions with complex geological structures.The engineering geological conditions are complex and the stress is high.The rock burst and large deformation disasters in the tunnel construction which are closely related to the high ground stress are increasing.These disasters resulted in significant economic losses,casualties and delay in construction period,which caused great difficulties for the construction of the project.Therefore,it is very necessary to carry out the research on the construction risk assessment of the highland stress tunnel,and establish a comprehensive and effective evaluation index system,evaluation model,rating standard and risk control system for the construction risk of high stress tunnel construction.It plays an important role in guiding the construction of high stress tunnel in the future and developing the risk assessment and management system of tunnel construction in China.It has significant engineering value and academic significance.In view of the characteristics of high stress tunnel construction,this paper discusses the risk factors identification,risk assessment and risk response of tunnel construction,combining the advantages of expert evaluation analysis method and risk matrix method,and focuses on the evaluation of rock burst and large deformation risk in high stress tunnel construction by using index system method.The main contents of this paper are as follows:(1)through collecting and sorting out a large number of high stress tunnel construction rock burst and large deformation case data,the causes and conditions of rock burst and large deformation in tunnel construction are analyzed,and three influential factors of rock burst and large deformation are summed up: geological factors,design factors and construction factors.And screening the main risk assessment indicators: rock strength,surrounding rock integrity,ground water conditions,stress size,section size,construction method,single cycle footage,support timing,support quality,pre support measures,blasting conditions,monitoring measurement and prediction of advance ground quality.Combined with the existing research results,engineering field investigation and expert consultation,the influence probability of various factors on rock burst and large deformation is calculated,which provides a powerful engineering practice basis for index scoring.(2)combining the advantages of expert evaluation analysis and risk matrix method,the risk assessment model of rock burst and large deformation in high stress tunnel construction is established by using a simple and highly operable index system.According to the score of the risk probability level,the probability grade is determined by the professional personnel,and the results of the risk loss of the more than 10 tunnel construction are statistically analyzed.From the angle of the rock burst and the large deformation intensity,the casualties,direct economic losses,and the expectation of the delay in the construction period are carried out.Quantitative estimation is used to get the severity grade.Then the risk matrix is used to get the risk level considering the possibility and severity of risk.Finally,the risk level is divided into low risk(I),moderate risk(II),high risk(III),and extremely high risk(IV).(3)Using the risk assessment model established in this paper,pre-construction and construction process risk assessments were conducted for the rockburst at the Micangshan tunnel and the large deformation of the Miyaluo-3 tunnel.According to the risk assessment results and the risk acceptance criteria,some effective risk control measures are proposed for the high risk tunnel construction section.The validity and practicability of this set of risk assessment models were verified.