| With the continuous expansion of urban scale and the rapid increase of urban population,the problem of saturated road traffic congestion caused by ground traffic resources has become increasingly prominent,and the exploration of urban underground space has gradually become the development trend.In the construction of urban tunnels,as the main force,shield machines often encounter soil-rock composite strata in the process of crossing strata.Compared with single homogeneous soil layer or rock stratum,such composite strata are more prone to engineering accidents such as excavation face instability due to improper control of soil bin pressure.The existing theoretical research on the stability of the excavation face does not fully consider the heterogeneity of saturated clay,the linear change of cohesive force with the depth of clay stratum and the influence of stratification coefficient in the composite stratum,which leads to the theoretical model can't accurately reflect the engineering practice.In view of the above problems,combined with the characteristics of the composite stratum of the limestone underlying saturated clay in the shield section of the West Olympic Center Station?Dingjiazhuang East Station of Jinan Metro Line 3,this thesis studies the failure mode and disturbance of the excavation face under the condition of the soil-rock composite stratum in this section by theoretical derivation and numerical simulation,aiming at analyzing the failure mechanism of the shield excavation face.The main contents and results are as follows:(1)In order to study the failure mechanism of excavation face in soil-rock composite stratum,based on the upper bound theory of limit analysis and the existing theoretical model of uniform soil layer,and considering the influence of heterogeneity and stratification coefficient of saturated clay,the numerical spiral instability failure mode of excavation face is constructed when shield passes through the composite stratum containing heterogeneous clay.The limit support pressure of excavation face is obtained by MATLAB software,and compared with the calculation results of theoretical model of industry scholars;the rationality of the optimized and improved theoretical model is verified.Based on the constructed theoretical model of shield tunnel excavation face in composite stratum,the influence of clay heterogeneity coefficient and layered coefficient on the ultimate support pressure is studied and analyzed.The results show that when the buried depth ratio of tunnel is constant,the ultimate support pressure decreases linearly with the increase of initial cohesion,and the sensitivity of the ultimate support pressure to the heterogeneity coefficient is weak.The initial cohesion becomes the decisive factor affecting the ultimate support pressure.The greater the stratification coefficient,the more sensitive the limit support pressure to the change of internal friction angle and cohesion.(2)In order to obtain a more realistic rock and soil simulation model based on the discrete element method theory and EDEM software,the secondary development program is used to quickly generate the virtual samples required for calibration.According to the indoor uniaxial compression test method and steps,the EDEM conducted a virtual uniaxial compression test,and completed the calibration of the meso-parameters of the Hertz-Mindlin with bonding contact model.The normal contact stiffness was 1.05×10~8N/m~3,the tangential contact stiffness was 7.25×10~7N/m~3,and the critical normal stress was The four mesoscopic parameters of5×10~8Pa and critical tangential stress of 5×10~8Pa can restore the mechanical properties of the target rock sample relatively completely;by means of the grey relational analysis method,the mesoscopic parameters required for the contact model and the mechanical properties of the rock and soil are established.The influence relationship between the macro parameters,the results show that the normal contact stiffness and tangential contact stiffness of the particle bonding bond in the contact model have the greatest influence on the elastic modulus,the impact recovery coefficient has a middle influence on it,and the stress ratio has the smallest influence on it..(3)In order to meet the needs of numerical simulation to further verify the correctness of the theoretical model,relying on the shield tunneling section between the West Station of the Olympic Sports Center and East Dingjiazhuang Station of Jinan Metro Line 3,based on the principle of the shield dynamic excavation system,the three-dimensional construction is used.The model software“Solid works”builds a simplified model of the shield machine.According to the engineering driving parameters and the calibrated rock and soil parameters,the EDEM simulation model is assigned and characterized,and the dynamic driving simulation process of the shield machine in the soil-rock composite stratum is realized.The medium gradient reduces the soil tank pressure of the shield,and the soil tank pressure when the excavation is faced with boundary instability is determined.Compared with the theoretical solution of the deduced limit support pressure,the error is within the allowable range,and the accuracy of the optimized theoretical model is further verified.The influence of factors such as tunnel burial depth ratio and saturated clay cohesion on the ultimate support force of the soil-rock composite stratum excavation face under different stratification coefficients is analyzed.The maximum displacement difference increases with the increase of the stratification coefficient,and the displacement changes more violently;the stratification coefficient of soil and rock is constant,and the initial cohesion of the clay is larger when the heterogeneity coefficient is larger,and the overall cohesion of the clay stratum increases,and the self-stability of the soil increases.The stronger it is,the peak lateral displacement decreases with the increase of cohesion when the excavation face is unstable.(4)In order to study the influence of shield tunneling on stratum disturbance,based on the dynamic tunneling process of shield tunneling in soil-rock composite strata under the EDEM simulation environment,the soil particles in front of the excavation front and in the soil bin during the shield tunneling process were analyzed.The law of movement and force was further studied under the action of the ultimate support pressure,when the shield tunneled in the soil-rock composite stratum with different stratification coefficients,the stratum disturbance law and influence range were further studied.During the excavation,the disturbance range of the excavation surface and the fluctuation of the particle velocity are large.The particle velocity of the soil at the edge of the shield is significantly higher than that of the central soil,and the particles have a tendency to creep upward.The surface subsidence at the axis accounts for about 14%to 18%of the overall subsidence,and the surface deformation also shows the same regularity as the subsidence range.From the beginning of shield tunneling to the monitoring section stage,the surface deformation rate increases with the increase of the stratification coefficient;The set value of soil bin pressure should be between 0.45 and 1.50 bar.When it is set to about 0.80 bar,the dynamic control is within the interval of 0.025 bar,which is more conducive to the control of the surface settlement of the soil-rock composite stratum and ensures the safety of the surrounding environment. |
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