Anisotropic Properties Of The Phyllite Strength Parameters And The Effect On The Large Deformation Of The Tunnel Surrounding Rock

Most soft rock tunnels have such problems as low strength of surrounding rock,large deformation,high in-situ stress and long duration,etc.The surrounding rock deformation has very obvious rheological property,and rheological property is an important factor causing large deformation of soft rock.The investigation shows that the deformation characteristics of the study section are different under different inclinations.Therefore,the study on the rheological anisotropy of surrounding rock is of great significance to the study of the large deformation of surrounding rock.In this paper,taking D5K218+090⁺105 section,D5K218+935⁺965 section and D5K222+100⁺120 section of a certain tunnel of Cheng Lan railway as the engineering background,considering the creep anisotropy characteristics of layered soft rock,and studying the anisotropy of strength parameters of phyllite rock at different dips.The composition of soft rock was determined by means of thin section identification and X-ray diffraction analysis;The mechanical properties of soft rock are studied by uniaxial compressive strength test,uniaxial and triaxial compressive deformation test and direct shear strength test.By considering the creep anisotropy of stratified phyllite and designing the compression creep test,The anisotropy characteristics of creep parameters of different dip angles phyllite were studied.and the influence of creep anisotropic characteristics of phyllite rock on the large deformation of the tunnel surrounding rock was studied.After research,the main results are as follows:?1?Through thin slice identification and X-ray diffraction analysis,it is found that the soft rock is phyllite,whose mineral composition is mainly quartz,followed by illite,mica and chlorite;Through the expansion test,it is proved that the phyllite in the tunnel site is non-expansion soft rock?2?Through the uniaxial compression strength deformation tests,it is concluded that the plane inclination angle of 0°,20°,45°,70°and 90°belongs to soft rock and soft rock.?uniaxial saturated compressive strength<30MPa?.Moreover,the anisotropy of uniaxial compressive strength,residual strength and elastic modulus was obvious,and all presented a u-shaped change with the change trend of the rock face inclination Angle.Through the triaxial compressive strength deformation test conclusion:At the same plane inclination with the increase of confining pressure,peak strength and elastic modulus are increased,and under the same confining pressure peak strength and elastic modulus changing with Angle for"U"type,a minimum of 45°.The parameters of other cohesive force C,internal friction Angle?,poisson's ratio,etc.Have little difference,anisotropy is not obvious.?3?Under different confining pressure?0 MPa?3 MPa?6 MPa?in creep test,When the dip angle of rock strata is 0°,20°,45°,70°and 90°,respectively,the typical failure modes of phyllite can be summarized into four kinds:tensile failure,shear slip failure,compression shear tensile failure,shear tensile failure.?4?The rheological model of 4-element Burgers is selected,which is composed of Max-well and Kelvin in series.It has the properties of instantaneous elastic deformation,deceleration creep and constant velocity creep,and can well reflect the rheological property of soft rock.Therefore,on the basis of a large number of triaxial creep tests,1stOpt software platform was used to fit the creep curve.test data fitting were obtained that the time-strain curve and rheological parameters such as E_M,E_K,?_M,?_Kand long-term strength.And found that the rheological parameters are anisotropic and have inclination effect.After that,The least square method is used to conduct fitting regression for the rheological parameters and dip,confining pressure,and the function is obtained:E_M=f??,?₃??E_K=f??,?₃???_M=f??,?₃?and?_K=f??,?₃?.The above results were substituted into the constitutive equation of Burgers model,and the improved creep constitutive equation with two variables of dipangle and confining pressure was obtained.The results provide a basis for the numerical simulation of the influence of phyllite strength parameters anisotropy on the large deformation of the tunnel surrounding rock.?5?Field monitoring data show that the surrounding rock deformation characteristics were numerically simulated with an improved Burgers constitutive model in FLAC^3D.During the construction process,the arch roof will be deformed by settlement and the floor will be deformed by upward rebound.?1?The dip Angle of 45°D5K218+090⁺105 section of arch roof largest accumulated subsidence value is206.0mm,113.7mm maximum peripheral convergence value;?2?The dip Angle of 70°D5K218 +935 + 965 section of arch roof largest accumulated subsidence value is 159.0mm,66.9mm maximum peripheral convergence value;?3?The dip Angle of20°D5K222+100⁺120 section of arch roof largest accumulated subsidence value is 139.0mm,51.0mm maximum peripheral convergence value.According to the above we can know that the dip Angle of 45°accumulated subsidence value and peripheral convergence value is relatively maximum,the dip Angle of 20°and 70°is relatively small.Combined with field monitoring data,FLAC^3D modeling software was used to simulate the deformation characteristics of surrounding rock.The comparison between the field monitoring results and the numerical simulation values shows that the numerical simulation values are generally larger than the field monitoring values,but the overall law remains unchanged.