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.