Model Tests And Theoretical Study On Earth And Water Pressure Of Shield Tunnel Under Seepage Condition

With China's rapid economic development and the promotion of modernization,the demand for cross-river and cross-sea traffic is growing.Cross-river and cross-sea tunnels have several advantages.A tunnel would not be affected by climate and still allow shipping to pass.Cross-river and cross-sea tunnels become an important way to connect citys,regions and contries.Loading is a basic problem in tunnel design and construction.Seeking for the mechanism of water and earth pressure on shield tunnel and establishing the calculation method have important significance in design and construction of cross-river and cross-sea tunnels under seepage conditionIn this thesis,model tests and discrete element method were used to analyze the magnitude and distribution of loosening earth pressure over the shield tunnel.The failure mode of loosening zone was also analyzed.Then the loosening earth pressures over the shield tunnel and failure mode of loosening zone under seepage condition were analyzed.Furthmore,the seepage flow field around cross-river and cross-sea tunnels was analyzed.The anisotropic permeability of surrounding rocks around tunnels were considered,the analytical solutions of seepage flow field of surrounding rocks,lings and grouting circle were obtained.Based on Terzaghi's loosening earth pressure theory,inclined slip surface were considered.The analytical solutions of loosening earth pressure under two dimensional and three dimensional conditions were obtained.The main work and innovation achievements are as follows:(1)A trapdoor apparatus was designed to study the classic trapdoor problem.A series of trapdoor tests with different soil depth ratio were conducted to analyze the loosening soil pressure and the failure mode of loosening zone.The distribution of loosening earth pressure on trapdoor was analyzed,and a modified analytical solution considering the stress distribution on trapdoor was proposed.In the meantime,Particle Image Velocimetry(PIV)method was used to obtain the displacement field and strain field of soil in loosening zone.The development of slip surfaces in the loosening zone was analyzed.(2)The trapdoor apparatus was then modified to study the loosening soil pressure and the failure mode of loosening zone under seepage condition.A series of trapdoor tests with different soil depth ratio and different seepage conditions were conducted.The loosening soil pressure and the failure mode of loosening zone under seepage condition were analyzed.A modified analytical solution considering seepage force was proposed to calculate the loosening earth pressure.(3)Three dimensional DEM(Discrete Element Method)software PFC3D was used to analyze the arching effect caused by the loosening of soil.A series of trapdoor tests with different soil depth ratio were conducted.The loosening earth pressure on trapdoor,the earth pressure in loosening zone and stable zone,and the coefficient of lateral earth pressure were analyzed.(4)Considering the anisotropic permeability of surrounding rocks and the effect of lining and grouting,the seepage flow field around cross-river and cross-sea tunnels was studied theoretically.The seepage flow field of surrounding rocks was obtained by coordinate transformation method and conformal mapping method.Then the seepage flow fields of lining and grouting circle were obtained according to boundary conditions and flow continuity conditions.A series of examples were conducted to confirm the validity and analyze the parameter sensitivity.(5)Based on Terzaghi's loosening earth pressure theory,the loosening earth pressure solutions under two dimensional and three dimensional conditions were proposed.The slip surface was assumed as inclined slip surface,the loosening earth pressure was solved using differential layer element method.The influence of soil depth ratio,length of loosening zone,parameters of soils,and coefficient of lateral lateral earth pressure on loosening earth pressure were analyzed.