Study On Time-dependent Characteristics Of Surrounding Rock Deformation In A Certain Tunnel Of Cheng Lan Railway

The soft rock tunnel has the problems of low rock mass,high ground stress,large deformation and long duration.The deformation of the surrounding rock has obvious rheological characteristics,and the research on the deformation characteristics of the surrounding rock of the soft rock tunnel should be paid attention to.Based on the relevant literatures at home and abroad,this paper takes the D5K218+790⁺860section of a tunnel in ChengLan railway as the engineering background.According to its regional geological characteristics,from the problem of temporal and long-term stability of soft surrounding rock deformation,the mechanics characteristics of the microclades and the mechanical properties of the microclades are analyzed by field investigation,site monitoring,laboratory test,theoretical analysis and numerical calculation.And the rheological properties of the surrounding rock are studied.The main conclusions following aspects:（1）The results of flake identification and the analysis of mineral composition show that the soft rock is phyllite and its mineral composition is mainly quartz,followed by chlorite,illite and mica.TheSwelling test,uniaxial compressive strength and compressive deformation test,direct shear strength experimentalof results show that the phyllite is a non-expansive soft rock with a comprehensive softening coefficient of 0.57.The quality of D5K218+790⁺820 and D5K218+820⁺860 is mainlyⅣandⅤ.（2）The shear stress-time curve of the phyllite is obtained under the saturated water condition.According to the isochronal cluster curve drawn by the rheological test,the long-term strength of the phyllite is 0.82MPa、0.87 MPa、0.96 MPa、1.05MPa。The internal strength of the long-term strength index is 0.769MPa,the internal friction angle is 22.40°（internal friction coefficient is 0.39）and the saturated shear strength parameter C is 0.997,theφvalue is 44.48°（internal friction coefficient is0.982）64%.The whole process curve of the creep of the phyllite is fitted by the Burgers model,which reflects the creep characteristics of the rock.The creep parameters obtained by fitting are E₁=1.04GPa,E₂=4.54GPa,η₁=218.33GPa·h,η₂=4.39GPa·h,the constitutive equation of soft rock shear rheology is established,and the rheological deformation of FLAC^3D is simulated Which will lay a foundation for the deformation characteristics of surrounding rock.（3）By plotting the deformation-time characteristic curve of the surrounding rock,the variation law of the surrounding rock deformation with time is analyzed emphatically,and the excavation curve is mainly"step".（4）The cumulative settlement of the surrounding rock and the cumulative value of the surroundings are obtained.The large deformation of the surrounding rock mainly occurs in the thin mantle and the carbonaceous mantle rock,and the deformation is large,the deformation time is long,the deformation rate is large,and the groundwater is seriously affected.The large deformation mechanism of the surrounding rock in the tunnel research area is not a single deformation mechanism,but also has a variety of deformation mechanism of the complex deformation mechanism.The stress and groundwater are the most important controlling factors for the large deformation of the surrounding rock in the tunnel research area.The stress expansion mechanism（Ⅰ₂）is the most serious deformation mechanism.（5）Through the numerical simulation of FLAC^3D,the maximum cumulative settlement value of the vault is 90.0mm and the maximum convergence value is70.0mm under the creep condition.Under the creep condition,the maximum cumulative settlement value of the vault is 49.7mm and the peripheral convergence value is the largest Is 20.0mm.（6）It is found that in the soft rock tunnel,considering the creep effect,the deformation and stress variation of the surrounding rock affected during the construction of the weak surrounding rock tunnel are more and more practical than no considering the creep model.Creep effect has a great influence on the deformation of surrounding rock during tunnel construction.