A detailed study of the CHN-BQ rock mass classification method and its correlations with RMR and Q system and Hoek-Brown criterion

A CHN-BQ method is firstly defined to present the system and connotation of the current Chinese national standard “Standards for Engineering Classification of Rock Mass” GB/T 50,218. The core idea and content of the CHN-BQ method are studied in detail. Based on a qualitative classification of rock masses at the sites of in situ rock deformation and shear strength tests with a total number of 1439 test sets in nearly 90 projects, the statistical characteristics of in situ test results of different grades of rock mass are analyzed; Thus, the mechanical parameters corresponding to each grade of rock mass basic quality are proposed. Based on 997 groups of various rock mass classification data in 10 projects, the comprehensive CHN-BQ method verifies, and some essential remarks are obtained. Firstly, the 312 sets of parallelly measured data show that the consistency of less than one-grade discrepancy of the qualitative and quantitative classification in the CHN-BQ method is up to 71% in percentage. Secondly, a highly linear correlativity of the CHN-BQ method with the RMR method is found, and a linear regression equation is proposed. Thirdly, a logarithmic regression equation between the CHN-BQ method and the Q system is obtained, and equivalent grading divisions of the Q system from 9-level intervals towards traditional 5-level intervals are proposed. Finally, the research shows that the GSI concept in the Hoek-Brown criterion and the qualitative classification of rock mass structure in the CHN-BQ method are essentially coincident. Based on the measured data in quartz mica schist rock of an arch dam project, a linear regression equation of the Kv index in the CHN-BQ method and GSI index in the Hoek-Brown criterion is obtained, and the comparison of the strength parameters of the CHN-BQ method and Hoek-Brown criterion is discussed.