Research On Tunnel Surrounding Rock Mass Stability And Risk Analysis Based On Uncertainty Theory

The analysis of tunnel stability and risk is a complex and uncertain problem . Inthe analysis process, there are a lot of random, fuzzy and unascertained information.Traditional deterministic analysis method can not reflect these characteristics. So,there are important theoretical signiticance and engineering applications to study thetunnel surrounding rock mass stability and its risk analysis based on the uncertaintytheory. Therefore, based on the discussion of tunnel surrounding rock massmechanical parameters determination method, the probability and statistics, fuzzymathematics and interval mathematics theory are used to study the tunnelsurrounding rock mass stability from the qualitative and quantitative analysis in thispaper. Whilely, the tunnel construction risk is evaluate d.Firstly, the determining method of the rock mass mechanical parameters isstudied. There is shortcoming to determine the rock shear strength with random fuzzymethod. The membership degrees of the rock shear strength test index values toestimated values are regarded as the fitting bias weights. Then, the fuzzy fittingmethod to determine the rock shear strength index values is proposed based on theleast square method. And the fuzzy random reliability and confidence interval on therock shear strength index values determination are analysised. The results of fuzzyfitting analysis method can not reflect the test data distribution . The non-symmetrictriangular fuzzy numbers are used to express the equation coefficients of rock shearstrength criterion. And the membership degres of test data to estmated values areregarded as the weight values to modify the deviation between the probabilitycalculation values and test data. Then, the summation of the weighted aquaredeviation and interval width of non-symmetric triangular fuzzy number with one cutlevel are regarded as the objective function to carry on the fuzzy optimizationanalysis. The determining method of rock shear index values with non-symmetrictriangular fuzzy number can be proposed.In order to get the rock mass mechanical parameters, the geological strengthindex (GSI) is used. But there are interval and fuzzy uncertainty during determiningthe geological strength index (GSI). So the interval number or fuzzy number is usedto express the parameter values. Then, the surface condition rating (SCR ) and jointcondition factor (Jc) are used to quantitate the values of surface conditions. The surface rating (SR ) and quantitative block volume (V b) are used to quantitate thevalues of rock structure. The method to determine the rock mass mechanicalparameters based on the interval theory and GSI or based on the fuzzy theory andGSI is proposed by the comprehensive use of Hoek-Brown strength criterion withGSI, experience determining formulas, interval optimization calculation methods andcut-level technique.Secondly, the stability of tunnel surrounding rock mass is studied by the rockmass classification and reliability analysis based on the determined rock massparameters. For the rock mass classification, the two-stage fuzzy synthetic judgmentmodel of rock mass classification is proposed according to the properties andfuzziness of the key effecting factors. The determining methods of the membershipdegrees to quantitative and qualitative indicators are discussed. The determiningmethods of weight vectors are also study. Then the idea of changing weight value isused to present the two-stage fuzzy synthetic judgment method with changing weightvalue of the tunnel surrounding rock mass classification. In addition, there is intervaluncertainty in the determining process of the membership degree s and weight valueson the evaluation index. And there is nonline feature during the judgement. So theinterval numbers are used to express the evaluation index values and the importancebetween each other. The determining method of interval membership degrees andinterval weight values as well as the nonline fuzzy calculation method are discussed.Then, the interval nonlinear fuzzy synthetic judgment method of the tunnelsurrounding rock mass clasification is proposed.For the tunnel surrounding rock mass reliability analysis, the triangular fuzzynumber s are used to represent the physical and mechanical parameters of rock mass.The reliability analysis function of tunnel anchor-shotcrete support structure isproposed based on the tunnel anchor-shotcrete support structure shear failure theory.The fuzzy possibilistic reliability analysis method of bolt-shotcrete support structurecan be estabilished based on the solving method of fuzzy reliability indexes. Throughthe limit analysis method, the reliability analysis function of rock mass unstableblock along with the single or double sliping surface under the given safety factor .Then, the fuzzy possibilistic reliability analysis method of rock mass unstable blockcan be estabilished. The fuzzy possibilistic reliability analysis method of rock slopcan also be estabilished by the same way.Thirdly, the tunnel construction risk is studied. Based on the fuzziness andhierarchy of the tunnel construction feature and effecting factors, the two-stage fuzzy synthetic judgment model of tunnel construction risk is established. There isuncertainty with importance values of the effecting factors when determining theirweitht values by AHP method. So the priority method of triangular fuzzy numbercomplementary judgment matrix is used to calculate the weight vectors. And the thenonlinear fuzzy matrix composition operating method is used to calculate the results.The nonlinear fuzzy synthetic judgment method of tunnel construction risk can besuggested. In addition, there is uncertainty with the effecting factors of tunnelconstruction support structure. The fuzzy possibility reliability analysis method isused to calculate the failure probability of tunnel support structure. And the resultgrade analysis method of tunnel construction support structure is present by nonlinefuzzy synthetic judgment method.Finally, the methods proposed in this paper are used to analysis the diversiontunnel engineering of Zhexi hydropower expansion project in Hunan provience. Theanalysis results verify the applicability and reasonableness of the tunnel surroundingrock mass stability and risk analysis method based on the uncertainty theory.