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Abstract The National Standard for Engineering Classification of Rock Masses(GB50218—94)，as a general rock masses classification standard，can be suitable to all kinds of rock engineering；it uses the method combining the qualitative description with the quantitative calculation to evaluate the rock masses quantity，and has been extensively applied to different rock-mass projects. Yet because the qualitative description content is relatively complex，the grading criteria is fairly rough；and when using the quantitative index BQ formula，it is necessary to consider two corresponding limiting conditions，the practicality of the BQ is effected to some extent. For the purpose of solving these problems，a graphic method is put forward to represent the national standard rock masses classification BQ，the intact rock uniaxial compressive strength Rc and the integrity index Kv of rock masses are chosen as the Y-axis and the X-axis，respectively；and the two limiting conditions are also considered into this method to draw the broken line graph. Using this graph，the rock masses classification can be determined conveniently，rapidly and accurately as the results of different rock engineering examples. Besides，in view of the local inconsistence conditions between the qualitative descriptions and the quantitative indices，some optimizations to the qualitative grades of the intact rock uniaxial compressive strength Rc and the integrity index Kv of rock mass are done according to the graphic results，the coincident degree between the optimized qualitative grades and the BQ value has been increased 3%–12% comparing with the original grades and the BQ values. At last，the choosing approach of two grade indices and the influence of modified factors to the graphic results have also discussed and analyzed by the chart. This research can provide some references to the latter modified and optimized to the national standard BQ.
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Received: 01 April 2011
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2012, Vol. 31 
