Timeliness of Creep Deformation in the Whole Visco-Elasto-Plastic Process of Surrounding Rocks of the Tunnel

Nishihara model is modified by using unsteady viscous body. By combining with Lade–Duncan criterion, this study analyzes the whole deformation process of surrounding rocks of tunnels at visco-elastic and plastic stages and calculated visco-elastic–plastic solutions for surrounding rocks of tunnels. By taking an expressway tunnel as the research object, the displacement of surrounding rocks in creep aging process is calculated and the creep deformation of surrounding rocks of the tunnel is measured by monitoring vault settlement on site. By comparing theoretical calculation value with field measured value, it is verified that the theoretical calculation is correct. The theoretical calculation shows that when t = 0, creep phenomenon occurs to surrounding rocks and the displacement of surrounding rocks is 17.890 mm. When t is a constant, displacement of surrounding rocks gradually increases with time. While t = ∞, surrounding rocks are completely crept and the ultimate displacement of surrounding rocks reaches 26.451 mm. The monitoring results on site demonstrated that the first stable accumulative deformation of vault of surrounding rocks was 19.1 mm. After entering into creep stage, the second stable accumulative deformation of vault was 29.3 mm. The error between theoretical calculation and actual monitoring result of initial creep deformation is 6.76%, while 10.77% of error is found between theoretical calculation and actual monitoring results of final creep deformation. The small errors between them reveal that theoretical calculation shows a high accuracy. Theoretically, deformation of surrounding rocks increases by 47.85% after considering creep effects. Actually, the deformation of surrounding rocks rises by 53.4% after taking creep effects into account. This reflects that creep effects play an important role. Therefore, as for the support design of tunnels in soft rocks, creep effects are bound to be taken into consideration to avoid failure of primary supports caused by creep effects of surrounding rocks at later stage and then influences on overall stability of the tunnel.