Abstract：The strength and mechanical parameters of large-volume jointed rockmass can be estimated by using Hoek-Brown criterion. The criterion has been generalized over the years，and the geological strength index(GSI) was introduced into the criterion by its originator. However，the quantitative description in structure of jointed rockmass is lacking，that leads to rough estimation of GSI values. In order to provide a more quantitative description in structure of large-volume jointed rockmass for evaluating GSI，modification of GSI is suggested by introducing parameter Jv (joint number / m3) with a computation example. The proposed method provides a new，economical and practical avenue for estimation on strength and mechanical parameters of large-volume jointed rockmass.
