Research Note

Inaccurate understand of creep behavior of the rocks and application of inappropriate behavior models can lead in uncompensable damages in the tunnel analysis and design. Fortunately, study of time-dependent behavior of rocks has been taken into consideration in recent years and even it has been considered in many of the most applicable soft wares such as FLAC. In this paper, the time-dependent behavior models of Maxwell, Kelvin-voit, Burger and CVISC have been presented. Subsequently, these models have been analyzed in the finite difference program of FLAC in a circular tunnel model in a hydrostatic condition, thereafter; the analysis results have been compared. Improving these models, a time-dependent model has been proposed and its performance has been verified by comparison with mentioned models. The most important attribute of the proposed model in this paper, is its advantages to take all three stages in rock masses creeping into consideration (this phenomenon occurs in high stress zones in deep part of rock masses). Furthermore, this model has the advantage of describing the softening behavior in stress-strain curve based on the reduction in rock mechanical parameters (In confronting to tertiary creep).