Investigation On Characterization And Influencing Factors Of Time-dependent Behavior Of Soft Sandstone Surrounding Rock In Tunnel

Sandstone is one of the most common sedimentary rocks in underground engineering,and it has remarkable characteristic in anisotropy.The failure progress of surrounding rock is time-dependent during the excavation of tunnel,and it is important to control the deformation in tunnel construction.Considering the rate sensitivity of sandstone,there are few studies on creep evolution law of surrounding rock,the effects of supporting structure stiffness and excavation speed on surrounding rock and the loading of surrounding rock and supporting structure.This thesis takes Yunfeng Temple tunnel surrounding rock of Hang-Chang highway as engineering background and main research object.With the combination research methods of indoor test,field monitoring,theoretical analysis and numerical simulation,this paper makes a systematic and deep research on the characteristics of the rate sensitivity and influencing factors of time-dependent behavior of surrounding rock in tunnel.Based on the analyses,the following conclusions can be reached:A series of uniaxial compression tests are performed with different loading rates in order to analyze the mechanical properties of sandstone.And then the basic mechanical properties and Stress-Strain cruves of saturated sandstone with different loading rate are obtained.The result shows that the peak stress and the loading rate are positively correlated.The peak stress of sandstone increase with the increase of loading rate,and hence the rate-dependent behavior of sandstone is obvious.An elasic-viscoplastic constitutive model is presented to predict the time-dependent behavior,which is based on stress integration algorithm and rate sensitivity.The model parameters of the proposed constitutive model are identified by the indoor uniaxial compression rate sensitivity test of weak sandstone,and the elastic-viscoplastic constitutive model is implemented into finite element software such ABAQUS by UMAT subroutine.The correctness of this model is verified.Comparison between the settlement of vault and the convergence rate of cave on different right section of YUN-FENG temple tunnel shows that the settlement rate of vault decreases with the increasing of time firstly,and tends to level off in the end.The convergence rate of surrounding rock is similar to the settlement of vault.Based on the elastic-viscoplastic constitutive model,the three-dimension numerical model of YUN-FENG temple tunnel is built by using finite element software ABAQUS,and the death and birth unit element technology is used.Time-dependent deformation and stress distribution of surrounding rock in tunnel entrance during the progress of excavation are discussed,meanwhile,the loading conditions of anchor sprouting is also analyzed.In addition,the influence of anchor sprouting thickness and excavation speed on deformation and stress evolution of surrounding rock and loading condition of supporting structure is simulated in detail.