Discussion on influence of initial support to stability and deformation of surrounding rock mass in soft rock tunnel

The deformation of surrounding rock mass has prominent rheological behavior while the tunnel was excavated. The deformation of surrounding rock mass was analyzed on the basis of Poyting-Thomoson model, and the characteristics of surrounding rock mass deformation under initial support were discussed according to the universal analytical viscoelasticity solution and the monitoring results of Shilong Tunnel of Yu(Chongqing)-Sha(Changsha) Expressway. Analogy surrounding rock mass under initial support or not with rock creep under uniaxial or triaxial stress. Initial support can diminish the permanent deformation value of surrounding rock in a certain extent, and reduce the deformation rate of tunnel surrounding rock greatly. These achievements are very helpful to the determining the time of secondary lining, and have instrutional significance and referential value for similar engineerings.