Study On Creep Behavior Of Tertiary Mudstone And Long-term Stability Of Tunnel

With the development of China's transportation industry and the expansion of scale and geographical of the project construction,we have encountered a transitional rock between the soil and the rock.Recently,the Taoshuping Tunnel,Humaling Tunnel and Zhongtiaoshan Tunnel,all passed through the Tertiary strata.The nature of the Tertiary strata is between the soil and the rock,and the cement is weak and softens when it meets water.Surrounding rocks have the characteristics of short time of self-stabilization,large deformation and obvious rheological characteristics,which will bring great risks to the project.Therefore,it is of great significance to the research of Tertiary strata.In this paper,based on the Zhongtiaoshan tunnel project of the Menghua railway,the creep properties of the Tertiary mudstone and its effect on the stability of the tunnel are studied.Through mechanical properties tests and numerical simulations,the physics of the tertiary mudstone is studied.Mechanical properties tests and uniaxial creep tests were conducted to study the creep properties of Tertiary mudstones,and the basic physical and mechanical parameters and creep constitutive model parameters of Tertiary mudstones were obtained.The viscoelastic analytical solution of the Zhongtiaoshan tunnel is analyzed analytically and numerically.The influence of rheological changes on the long-term stability of the tunnel is numerically simulated using FLAC3D.The deformation and safety factor under different working conditions are calculated.The main conclusions and results obtained are as follows:(1)The uniaxial strength of Tertiary mudstone is more discrete in natural state,and the uniaxial strength is less discrete in saturated state,and the softening effect is obvious.(2)When the loading pressure is small,the creep of mudstone becomes steady-state creep.When the loading pressure is large,the creep of mudstone belongs to non-steady state creep and eventually leads to damage.The steady state creep rate and the loading pressure are linear after the logarithm is taken.With the isochronal curve and the average creep rate curve,the long-term intensity range was determined.In addition to accelerating the creep stage,the use of Burgers model to fit the test results,the effect is good.(3)According to analytical calculations,the interaction force between surrounding rock and support structure increases with time,and the growth rate gradually decreases,but the stress is not stable until 100 years.The safety factor keeps decreasing with time,but there is still a certain amount of safety reserves after 100 years.(4)Using FLAC3D to analyze the long-term stability of the tunnel and analyze thestress and deformation of the surrounding rock and lining of the tunnel.After 100 years of creep calculation,there is still a large safety reserve to meet the requirements for tunnel use.When the burial depth is 100m and 70m,the tunnel depth has a great influence on the deformation of the lining in the vertical direction,and the impact on the horizontal convergence deformation is relatively small.(5)Tertiary mudstones are softened by water and rheological effects are more pronounced.Therefore,in the case of tertiary mudstones that are saturated or have a high water content,attention should be paid to precipitation and support.