MECHANICAL ANALYSIS OF SEGMENT FLOATING DURING SHIELD TUNNEL CONSTRUCTION

The lining segment is in a complex stress state during shield tunnel construction,which is prone to go dislocation and have wholly rising displacement.Based on the analysis of segment in grouting section and considering static buoyancy and dynamic buoyancy,the buoyancy is respectively analyzed during shield tunnel construction.The mechanical model for segment ring in floating phase and calculation formula are presented,respectively.Aiming at the difference of segment ring between normal design state and floating state,the modified routine method is carried out to calculate lining internal force to draw a comparison.The results show that,comparing with segment ring in the normal design state,the bending moment,shear force and axial force values of segment increase by 60%,51% and 46% in floating state,which indicates that segment floating is adverse to its safety.The stress of segment is affected by dynamic buoyancy greatly during construction stage,which is larger than static buoyancy and must controlled reasonably for preventing the segment fracture.