| Compared with the single stratum shield tunnel,the shield tunnel in the upper soft and hard stratum has the characteristics of horizontal soft and hard uneven formation,frequent mutation in the longitud inal direction,and the outstanding problems of structural stress and uneven settlement.Compared with the small diameter shield tunnel,the super large diameter shield tunnel has a large section,the segment and the joint are numerous,the structural material and the geometric nonlinear characteristics are remarkable.At present,the structural design of the super large diameter shield tunnel in the upper soft lower hard stratum is often designed by analogy to the structural design of the super large diameter shield tunnel in the soft soil layer,and for the treatment of the bedrock at the bottom of the tunnel,only a small diameter shield tunnel project can be used for reference.In view of this,the lateral design calculation model,the longitudinal design calculation model of the super large diameter shield tunnel in the upper soft and the hard stratum and the treatment measures for the base rock engineering at the bottom of the super large diameter shield tunnel are carried out by the methods of literature investigation,theoretical analysis,numerical simulation and numerical test.The main conclusions of this paper are as follows:(1)The influence of shield construction on the pressure fluctuation of the shield tail slurry is explored,and the grouting pressure load is obtained when the size of the slurry fluctuates.According to the above research results.the calculation model of the cross section load of the shield tunnel in the upper and soft lower hard stratum is established by combining the method of taking the load value method of the upper soft lower hard stratum and the comprehensive resistance coefficient method.Based on the calculated model,the influence of bedrock embedment and bedrock dip angle on the stress of super large diameter shield tunnel is analyzed.(2)By analyzing the longitudinal deformation mode and the theoretical calculation model of the shield tunnel,it is concluded that the longitudinal beam-spring calculation model is applied to the longitudinal calculation model of the shield tunnel in the upper soft lower hard formation.According to the characteristics of the longitudinal bolt connection of the lining,the calculation formula of the shear stiffness of the connecting bolt is obtained according to the Timoshenko theory.The shear stiffness of the longitudinal connection of the shearing force of the shear pin is taken into consideration by the numerical simulation test.According to the longitudinal calculation model,the longitudinal stress characteristics of the tunnel structure with or without the shear pin are analyzed.(3)The structural mechanics characteristics of the super large diameter shield tunnel under the hard rock bulge at the bottom are analyzed by establishing a large three-dimensional calculation model co nsidering the joint bolt and shear pin stiffness of the shear pin.Through the calculation of the ANSYS finite element software and the theoretical analysis,the difference control standard for the longitudinal formation of the tunnel structure is obtained.Through the investigation and analysis,the field control standard of the base rock blasting based on the RQD index is obtained,and the improved structure of blasting charge for bedrock blasting is put forward.(4)The whole structure of the Maliuzhou tunnel in Zhuhai was tested on site.The law of stress variation of the segment structure of the super large diameter shield tunnel during the whole construction process is defined.Based on the engineering of Ma Zhou Zhou tunnel,the lateral and longitudinal calculation models of the super large diameter shield tunnel,the shear pin and the improved charge structure of the bedrock blasting are applied and verified in the field. |
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