The Evaluation Methods Of Tunnel Geological Hazards Based On Uncertainty Theory

The influence factors of tunnel geological hazards and its influence mechanismhave significant uncertainty in the tunnel construction process. However, traditionaldeterministic analysis methods can not reflect this characteristic. Thus it hasimportant theoretical significance and engineering application to study evaluationmethods of tunnel geological hazards based on uncertainty theory. Based upon this,the combination evaluation method、set pair analysis method、D-S evidence theory andinterval non-probabilistic reliability analysis method were introduced in this thesis,according to the characteristics of surrounding rock quality classification、 tunnelcollapse、rock burst and karst water bursting, meanwhile, according to the differentcharacteristics of surrounding rock mass classification and tunnel engineeringgeological disasters, the corresponding uncertainty analysis and evaluation methodswere established.Firstly, the method of tunnel surrounding rock quality classification was studied.Considering the inconsistency among the evaluation results drawn by differentclassification methods of surrounding rock quality of tunnel, combination evaluationidea was introduced in this thesis. A calculation model of surrounding rock qualityclassification based on combination evaluation was formulated by selecting severalexisting classification methods of surrounding rock quality of tunnel as the fundamentmethods, which can combine the advantages of several fundament methods. Due tothe divergence of physical meaning and dimension of evaluation indexes drawn byfundament methods, a standardized method for evaluation indexes was developed tomake evaluation results of different fundament methods have commensurability andto resolve computational problem of the calculation model based on combinationevaluation. Taken into account the differences of rationality between the evaluationresults of fundament methods, a measure method for reasonable degrees of fundamentmethods was set up by introducing drifting degree, on which the weight calculationwas developed. Then combination evaluation method of surrounding rock qualityclassification of tunnel was developed.For the study of tunnel collapse, based on a comprehensive analysis of the riskfactors of tunnel collapse, the main factors were identified, and a two-stage syntheticassessment model of collapse risk of mountain tunnel was formulated on the first stage. Then according to the feature that determinacy information and uncertaintyinformation of evaluation indexes cosexisted, set pair analysis theory was introducedto establish connection degree evaluation matrixes, which can comprehensivelydescribe the relationship between evaluation indexes and risk ranks from three aspectsof identity, difference and antagonism. Considering the uncertainties of theimportance degree of evaluation indexes, limitation of experts’ recognition anddifference of experts’ reliability, the method of uncertain analytic hierarchy processbased on group decision was formulated to calculate the weights. Then set pairanalysis method of collapse risk during construction of mountain tunnel wasdeveloped.Moreover, the disaster prediction method of rock burst was studied. Thecompound criterion based on several single criterion for rock burst was set up toreflect the influence of the stress state in sounding rock mass、lithological character ofrocks and the storage of elastic strain energy in rock mass. According to theinformation fusion feature of criterions for rock burst and by introducing D-Sevidence theory, the combination rule of criterions to rock burst was set up, which canreflect the consistency of information and conflict relationship of criterions for rockburst. In view of the deficiency of existing determination methods for basicprobability assignment function and taking into account the interval characteristics ofrock burst criterions’ classification standard, the definition of distance ofinterval-numbers was introduced and improved to set up the determination methodsfor basic probability assignment function. Then the disaster prediction method of rockburst based on D-S evidence theory was established.Finally, the safety thickness of tunnel face’s dike to prevent water irruption wasresearched with shear failure model. The characteristic of ground stress in differentcategory of initial stress field was analyzed to provide reasonable basis for thedetermination method of the normal stress on shear surface when tunnel face’s dikewas suffering shear failure. Tunnel excavation would cause stress redistribution, androck mass stress state before and after tunnel excavation is significantly different.Based on this feature the calculation method of the normal stress on shear surface wasset up when tunnel face’s dike was suffering shear failure. According to the intervalcharacteristics of parameters the interval non-probabilistic reliability analysis methodwas introduced to establish the calculation method of safety thickness of tunnel face’sdike to prevent water bursting.