Abstract: The method of fuzzy synthetical assessment applied to rock mass classification results in losing information of judgment, then influences veracity and reliability of the result. In allusion to the limitation, the theory of barycenter of fuzzy set is imported. Because weights of some factors is relative small, if using usual fuzzy synthetical assessment method, it will result in phenomenon of “submerge”. However, this problem does not exist now. Based on this theory, the six more important influential factors for rock mass classification such as index of rocky quality, uniaxial strength of renitency, integrated modulus of rock mass, soft modulus of rock, maximal seismic intensity and osmotic quantity of groundwater, are chosen; then the normal distribution as its membership function and the theory of the mean are used based on proportion to conform weights of the whole factors. Thus the method of rock mass fuzzy synthetical classification based on the theory of fuzzy set has been established. The calculational method of barycenter of fuzzy set of the whole factors is clarified combining a material project example. Finally, the method of rock mass fuzzy classification based on the theory of barycenter of fuzzy set is used to research the steady classification of a certain underground wall rock. Compared to the result of the method of fuzzy synthetical assessment and the actual steady instance of the wall rock, the veracity and the applicability of the textual method are validated.

Key words: theory of barycenter of fuzzy set, rock mass classification, membership function, weight