Time Effect Of Surrounding Rock Deformation And Support Mechanical Property Of Soil Tunnels

Due to the existence of the soil rheological property,the deformation of tunnel surrounding rock and the supporting pressure change with time.The size and the distribution of the surrounding rock deformation and support pressure are the important basis for the design of the tunnel structure,the lining support and the selection of construction methods.A new three-dimensional elasto-viscoplastic(3D-EVP)constitutive model is proposed by to reflect the stress-path-dependent property and the time-dependent property.The 3D-EVP is able to model the typical stress path of the decrease of the hydrostatic pressure,which is coincide with the tunnel excavation.Furthermore,the 3D-EVP is applied into the finite element modelling by the program of the User-Defined Material(UMAT).The Numerical model of tunnel excavation is built to research the soil rheological properties.The effect of the tunnel radius R,the buried depth H of tunnel and the stiffness of the tunnel support is discussed.The rules of the surrounding rock deformation and the supporting pressure calculated at 5 years are studied and described.The main innovations are listed as follows:(1)Based on the isotropic compression law of soil,the total deformation of soil is divided into instantaneous and time delayed.Referring to the calculation methods for instantaneous and delayed compression of United Hardening(UH)model,an onedimensional(1D)elastic-viscous-plastic(EVP)constitutive model is developed.On the basis of an elastic plastic(EP)constitutive model for soil considering the stress path dependency,a 3D EVP model is proposed by combining the delayed compression law under isotropic condition of the 1D EVP model and the instantaneous law influenced by OCR and shear stress ratio.The new model contains 7 material parameters,physical significances and determination of parameters have been analysed and given.Comparisons between model predictions and experimental results show the 3D model can describe viscosity properties of clay and sand reasonably under not only conventional stress path,but also special stress path of stress ratio loading under excavation.Based on the 3D EVP constitutive model,a numerical model considering time-effect is developed,and then been verified with enginerring datas.(2)The effect of time on the settlement of the ground and the vault is studied and discussed by the numerical method.For unsupported tunnels,the ground surface settlement calculated at 5 years is 53.2%~201.2% higher than the time when the excavation is completed.This ratio increases with the increase of H and decrease with the increase of R.The ratio of the vault settlement ratio calculated at 5 years can reach to 38.9%~107.2%.The ratio of the vault settlement increases with the increase of the surrounding rock rheological parameters y,and decreases as R increases.However,for supported tunnels,the ground surface subsidence ratio calculated at 5 years reaches to 78.0%~225.9%.This ratio increases with the increase of y(11)R and E,and decreases with the increase of H.The result of the rheological sedimentation at 5 years is taken as the final settlement and a reference.The settlement values of the ground and the vault for unsupported tunnels in an hour are 30.9%~43.3% and 17.3%~38.3% of the final settlement respectively,and the settlement values of the ground for supported tunnels are 0%~49.3% of the final settlement.(3)The effect of time on the radial pressure of the surrounding rocks and on the shear force and the bending moment of the tunnel lining is analyzed.The cross section of the largest internal force change is taken as the research object.For the rheological pressure,the aim cross section is the arch bottom.The rheological pressure calculated at 5 years is 31.3%~79.6% higher than the time when the excavation is completed.This ratio increases with the increase of y and decrease with the increase of R and H,and independents of E.For the rheological shear stress,the aim cross section is the spandrel.The ratio of the spandrel rheological shear stress ratio calculated at 5 years can reach to 28.7%~61.3%.This ratio increases with the increase of y and H,decreases with the increase of E,and independents of R.For the rheological bending moment,the aim cross section is the arch bottom.The ratio of the spandrel bending moment ratio calculated at 5 years is 35.5%~115.8%.The ratio increases with the increase of y,R and H,decreases with the increase of E.The variation of the rheological pressure,the rheological shear stress and the bending moment in an hour are 30.1%~39.5%,33.6%~49.0% and 26.9%~40.0% of the final settlement respectively.