Abstract: As mining depth increases, the large deformation of soft rock, such as roof fall, floor heave and two-side movement of the tunnel, poses a severe challenge to safe mining. Currently, continuous-discontinuous methods, combining advantages of both continuous and discontinuous methods, are rapidly developing. However, creep has not yet been introduced into these methods. Based on the experimental phenomenon that rock creep failure strain occurs in the post-peak region of the triaxial compression stress-strain curve, the viscoelasticity of the element is considered. A creep shear cracking model is developed to account for the viscoplasticity of the interface, and a criterion of creep shear cracking is introduced into the combined Lagrangian-discrete element method (a kind of continuous-discontinuous method) to simulate the creep shear cracking. The calculated creep curve under uniaxial compression aligns closely with experimental results. Once creep shear cracking begins, the specimen enters the accelerated creep stage. The proposed method has the potential to simulate accelerated creep. Results of the soft rock tunnel indicate that discrete blocks move into the tunnel due to the pushing of deep rock, sharply reducing tunnel size. Macroscopically, the tunnel exhibits a large deformation. The tunnel’s vertical shrinkage rate can reach 58.8%. The mechanisms of large deformation in the soft rock tunnel, attributed to the viscoelasticity of the element and the viscoplasticity of the interface (fictitious crack surface), result from a combination of small viscoelastic deformation of the medium, large block displacement, and viscoplastic deformation of the interface. It is unnecessary to describe the tunnel’s macroscopic large deformation using complex large deformation theories.

Key words: soft rock, creep, large deformation, surrounding rock of roadway, continuous-discontinuous method, viscoelasticity, shear cracking