Abstract: Firstly, the importance of study on mechanical parameters of rock mass is presented, and some methods to determine mechanical parameters are introduced, whereas their accuracy are questionable and argument. As there is difficulty in determining the disturbance factor D relayed on the Hoek-Brown strength criterion, fuzzy comprehensive evaluation is employed. Considered the factors influencing on disturbance and relevant engineering experience, the value of D is calculated accordingly, which is more corresponded to the practicality. Afterward, the rationality, that the bounds characterized by slip surface for dividing disturbed and undisturbed zone, is discussed; and it overcome deficiency of other expressions. Additionally, to further verify the reasonability and significance of such dividing, and with a practical engineering, calculation of the factor D is given using the modified and other methods respectively. According to the comparative analysis, it is shown that the former is more suitable to the disturbance degree in-situ.

Key words: Hoek-Brown strength criterion, fuzzy synthetic evaluation, disturbed factor D, disturbed zone