Abstract: In west China, a certain number of mining areas are in the mud weakly cemented soft rock strata; these soft rocks have the properties such as poor cementation, low strength and mudding when encountering water. Rectangle is a common pattern of mining roadway, but the wall rock stress is nonuniform and its stability is poor. In the soft rock strata, the rectangular roadway bearing capacity is low, and deformation is large and will last for a long time; these bring great difficulties for the safety of coal mine production. The belt crossheading rectangular tunnel of the new Shanghai No.1 coal mine in Inner Mongolia is taken for example, the rectangular tunnel deformation and failure are simulated through the Cvisc viscoelastic plastic model of FLAC3D. The simulation results are compared with in-situ monitoring values. The results show that: Influenced by cross-section shape, compressive stress concentrate in the four corners, zone of tensile stress is significant in the roof, roof subsidence is big, the floor heave and sides deformation are serious. Influenced by surrounding rock lithology, surrounding rock mass plastic zone is bigger and it causes support structure is difficult to fully play the effect, and surrounding rock appears the phenomenon of whole sliding. In addition, the deformation of surrounding rock exhibits rheological deformation characteristics, deformation quantity increases with time, continuous creep deformation is beyond the controllable limit of support body, eventually causes the instability and failure of the tunnel.

Key words: soft rock, rectangular roadway, deformation, failure, numerical simulation