Abstract: Most of the existing damage initiation criteria of rocks are functions of stress tensors, i.e. they are fixed surfaces in stress spaces. Hence the obtained damage initiation surface is a fixed surface between the initial yielding surface and failure surface. Based on assumptions in the existing damage initiation criterion, a damage initiation criterion for rocks taking creep deformation into account is proposed. According to this damage initiation criterion, the damage initiation surface in stress space will shrink with the increase of creep deformation. As a result, even when the stress levels are below the transient damage initiation values, damage will be activated due to the accumulation of creep deformation and will finally lead to rock failure. The damage initiation criterion could well explain the creep test results (such as results from constant strain rate tests, constant loading rate tests and constant loading creep tests). Parameters contained in the criterion can be identified by triaxial compressive tests and uniaxial creep tests.

Key words: rock mechanics, creep, damage, damage initiation, triaxial test, uniaxial creep tests