Study On Longitudinal Stability Of TBM Tunnel Structure In Chongqing Representative Strata

With the rapid development of TBM tunnel in our country,it is very important to ensure the stability of TBM tunnel in strata especially in mix ground such as Chongqing formation.The stability of TBM tunnel lining structure is influenced by many factors such as surrounding geologic strata environment,lining structure form and construction technology,etc.The design of TBM tunnel lining structure is based on relevant experience of shield tunnel design at present because lack mature theory,but this method usually cause serious waste of resources because the design method is conservative in order to ensure the long-term stability of the tunnel lining structure.This paper studies the longitudinal stability of TBM tunnel lining structure in mix strata in Chongqing.The main research work of this paper includes two aspects which contain influencing factors of stability of tunnel lining structure and calculation methods of different models.This thesis researches the modification of beam-spring model and analyses the influencing factors of stability of the tunnel lining structure such as joint bending stiffness,resistance coefficient of formation,lateral pressure coefficient and splicing system of segments,etc.Meanwhile,theoretical derivation and verification of finite element numerical simulation of the longitudinal equivalent continuous model is adopted to research the stability of TBM tunnel lining segments.Furthermore,this paper takes transverse effective rigidity ratio which is used to reflect the lateral performances of tunnel segments into consideration in the research process of longitudinal equivalent continuous model.The main jobs of this thesis are as follows:(1)In order to solve problems in the process of simulating actual tunnel segments by beam-spring model,this thesis introduces a new model named modified beam-spring model based on beam-spring model through combining the theoretical basis of beam-joint discontinuous model and shell-spring model.The new model uses the double nodes form of beam-joint discontinuous model on joints to solve the discontinuous problem of force.Meanwhile,the new model introduces radial and tangential bending stiffness theory and shear stiffness theory on joint spring.(2)The mechanical properties of segments joint of TBM tunnel with 6m outer diameters and 10 m outer diameters are analyzed by creating three-dimensional numerical model.The relationship between loads and turning angle of segments joints and the relationship between loads and bending stiffness of segments joints are found.The moment(absolute value)can increase turning angle of segments joints when the transverse axial force is constant.The bending stiffness K_θ tends to be stable when the moment M is less.With the increase of the moment M,the bending stiffness K_θ gradually decreases and tends to be stable at last.Furthermore,the axial force can enhance bending stiffness of segments joints.Meanwhile,this paper finds the value range of bending stiffness K_θ through the principle of tangent method based on θ-M curve.(3)This paper finds that resistance coefficient of formation,lateral pressure coefficient and splicing system of segments have influence on the stability of TBM tunnel lining segments and reveals relevant laws and degree of influence by researching the formation factor and splicing system of TBM tunnel segments.(4)Through the comparative analysis between theoretical derivation and finite element numerical simulation,the relationship curve between transverse effective rigidity ratio and longitudinal equivalent stiffness is found.Meanwhile,the linear effect of transverse effective rigidity ratio on longitudinal equivalent bending stiffness is revealed.The accuracy of influence law is proved by numerical simulation method.