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.