Typical rock samples of weak broken surrounding rock are collected from Tianpingshan Tunnel for Guiyang-Guangzhou railway. The conventional triaxial compression and triaxial compression creep tests are also carried out in the test room. Based on the results of rock tests

the creep characters of carbonaceous shale are studied. Only decelerating and steady creep stages appear under a low stress level. In the higher stress level

accelerating creep doesn’t appear. However

increasing confining pressure has raised the yield strength of the rock to some extent; and the elastic modulus also tends to increase. According to these

the viscoelastic plasticity strain softening creep model of the carbonaceous shale with whole creep process is established; and the constitutive function of this model is deduced under three dimensional stresses with its parameters confirmed. The creep parameters are identified by least square method. The comparison between creep model and test curve shows that the proposed creep model can reflect the creep characters of carbonaceous shale in background project; and it can be used to study the creep properties and stability of weak broken surrounding rock of this tunnel.