IMPROVEMENT OF BQ CLASSIFICATION FOR LAYERED ROCK MASS QUALITY INDEX IN TUNNEL ENGINEERING

The Standard of Engineering Classification of Rock Masses(BQ system) is a classification method of multi-factors,multi-variables,and qualitative and quantitative combination. In this method,we select the rock saturation uniaxial compressive strength and rock integrity index to calculate the value of the rock mass basic quality BQ. The modification of rock mass is made considering the field conditions of engineering rock mass,which makes BQ classification method ensure the objectivity of classification,and also reduces the difficulty of the scene classification. However,in some complex geological conditions,such as layered rock mass,BQ classification has the limitation of qualitative evaluation of correction coefficient. The actual use of the subjective judgment due to different field engineers,in the junction of two types of rock classifications,often occurs classification phenomenon. This paper expounds the influence law of angle of bedding and confining pressure on mechanical parameters of layered rock mass based on laboratory mechanics test. Jaeger-Donath and Mogi-Coulomb strength criteria are used to propose the calculation formulas of structural surface shape correction K₂ and initial ground stress state correction coefficient K₃. Finally,we verify the modification by the calculation of surrounding rock classification of Muzhailing railway tunnel.