Research On The Method And Application Of Rock Burst Risk Assessment In The Construction Of High Ground Stress Tunnels

With the implementation of the national"13th Five-Year",the planning study of the Sichuan Tibet railway and other western major projects have been gained project approval.Due to the effect of the India plate and the Eurasian plate,high geostress is formed under high geostress region in southwest china,the deep buried high geostress stress tunnel project will continue to appear.Under such bad geological conditions,as one of the most important geological hazards in high geostress,Rock burst always happen during the process of tunnel project.Besides,there exist the time of abrupt change and spatial uncertainty of tunnel risk accident.At present,although the incidence rate of rock burst is no higher than other geological hazards such as landslides,gushing water in the construction of the tunnel.Engineering cases of rock burst accidents revealed that Rock burst accident have influence on tunnel system engineering and the normal operation of the basic life and property safety.As an important part of the tunnel risk assessment,Rock burst risk assessment should not be ignored.The research on the risk assessment technology of tunnel rock burst is the foundation of reducing the geological hazards of rock burst,which is an important supplement to the risk assessment of the tunnel project,and which has important theoretical and practical significance.We can analysis the rock burst safety risk factors in construction process of the tunnel with the rock burst mechanism and theory.High geostress tunnel rock burst can be evaluation by using qualitative and quantitative risk assessment method.And then discuss the severity of the risk of rock burst with the characteristic of the tunnel excavation process,the relationship between the rock burst and affected bodies,the economic and personnel losses.（1）Firstly,the causes and conditions of rock burst are analyzed according the 28rock burst cases.The influence factors based on statistic induction such as lithology,rock integrity,rock strength,geostress,tunnel buried depth,section area and groundwater can be classification and probability calculation。Finding out the relation between the rock burst risk and the influence factors,and provide a strong engineering practice support for the index system.Collecting the method of Criterion of rock burst intensity and parameter index is intend to providing support and basis of the qualitative and quantitative evaluation of the high geostress tunnel of tunnel rock burst.（2）According to the general requirements and procedures of Guide for safety risk assessment of highway bridges and tunnels,a set of evaluation system for the risk of rock burst in tunnel is established.Selecting the rock lithology,integrity,rock strength,geostress,groundwater,tunnel depth and section area and other factors to establish the evaluation index system of rock burst.Using attribute mathematical method to verify the accuracy of the evaluation of rock burst index system on the evaluation of rock burst,which is more complicated and inconvenient for the evaluation process Compared with the index system.Combined with the characteristics of each working procedure of the tunnel project,the combination of the rock burst intensity and the sub section of the tunnel project to evaluate the magnitude of the severity of the rock burst is combined.Finally,besides a simple analysis of the disaster affected body and interaction relationship.And according to their own standards,from the aspects of the casualties,economic losses and the delay of construction period,the principle of the grade our ownership is determined.Finally,depending on the project of Erlang mountain of YaKang high-speed,the tunnel rock burst assessment techniques is applied in Erlang mountain engineering.（3）The Bayesian posterior probability theory is chosen as the quantitative evaluation method of rock burst risk in tunnel construction.According to the rockburst selection of risk ratio of stress intensityσ_θ/σ_c,elastic strain energy index W_ett and ratio of compressive and tensile strengthσc/σt.Combined with the collection and sorting out of the 51 learning samples,the quantitative model of the rock burst risk assessment theory is established by MATLAB program.Through the analysis of the rate of false positive,the final sample accuracy rate reached 90.2%.This method can be used to get the probability probability value P₁,P₂,P₃ and P₄ of no rock burst,Ⅰgrade rock burst（Slight rock burst）,Ⅱgrade rock burst（Medium rock burst）,Ⅲgrade rock burst（Strong rock burst）,which greatly improves the quantitative of the evaluation.The verification results are basically consistent with the actual situation in the next 6 validation samples,which indicates that the evaluation of rock burst by using this method has certain applicability and correctness.In the evaluation of the severity of rock burst,the impact factor of the no rock burst,Ⅰgrade rock burst,Ⅱgrade rock burst,Ⅲgrade rock burst is used to calculate the accident loss.According to the loss standard,a comprehensive unified monetary measurement loss standard is established.Finally raised the possibility and losses of all levels combined with the total risk of accumulation.And then MiCang mountain tunnel project of BaShan high-speed as an example,the method of risk assessment for rock burst in the tunnel construction is verified by the preliminary application.（4）Referring to the idea of PDCA product quality management cycle,a set of ERPAC management mode suitable for the risk management of rock burst in tunnel construction is put forward base on the characteristics of the rock burst under the condition of high geostress which including Excavation,Register,Plan,Act,Check.The cooperative relationship between the parties in the risk management mechanism is discussed,and the responsibilities of the parties in the management unit are defined,and the role of the management factors in the construction of the geostress tunnel construction is improved actively.