Creep　often　occurs　in　tunnels　excavated　in　soft　rocks　and　it　poses　a　risk　to　the　long-term　stability　of　the　excavation.　To　derive　measures　for　the　effective　mitigation　of　the　risk,　it　is　important　to　understand　the　time-dependent　damage　mechanism　governing　the　deformation　behavior　of　the　surrounding　rocks.　A　new　creep　constitutive　model　for　soft　rocks　was　proposed　in　this　study　to　help　achieve　this　understanding.　The　new　creep　model　was　developed　based　on　the　disturbed　state　concept,　for　example,　the　relatively　intact　state　of　rocks　was　described　by　the　Burgers　model　and　the　fully　adjusted　critical　state　was　represented　by　the　generalized　Bingham　model.　The　analytical　solution　from　the　proposed　model　was　given　and　the　parameter　calibration　based　on　uniaxial　compression　creep　experimental　results　were　described.　The　deformation　estimated　by　the　proposed　model　was　demonstrated　to　be　in　better　agreement　with　experimental　data　than　that　estimated　by　the　Burgers　model　alone.　In　addition,　a　three-dimensional　creep　constitutive　model　was　proposed　based　on　the　one-dimensional　form　with　the　assumption　of　the　constant　bulk　modulus.　A　case　study　for　a　tunnel　with　extensive　time-dependent　deformations　was　conducted　using　FLAC3D　with　the　incorporation　of　the　proposed　three-dimensional　creep　model.　The　results　indicated　that　the　proposed　creep　model　performed　well　in　the　prediction　of　the　time-dependent　deformations　and　failures　in　the　section　of　the　tunnel　being　studied.　This　model　provided　a　very　useful　tool　for　engineers　when　determining　the　design　for　excavations　and　ground　support　schemes　for　tunnels　in　soft　rocks　where　significant　creep　behaviors　must　be　considered.　©　2020　American　Society　of　Civil　Engineers.