Influencing Factors of Shield Tunnel Segment Floating in Muddy Siltstone Stratum

Abstract

Objective When shield tunnels crossing water-rich muddy siltstone stratum, the phenomenon of multi-ring tunnel segment overall floating often occurs, leading to quality defects such as segment damage, misalignment, and attitude exceeding limits. To ensure the quality of shield tunnel formation, it is necessary to study the influencing factors on segment floating. Method Based on the longitudinal stiffness reduction theory of shield tunnel and the stress characteristics during segment construction, a finite element analysis model of longitudinal overall floating during segment construction is established. The influence law of segment lining structure longitudinal rigidity, dynamic and static buoyancy factors on long-distance and large-scale floating deflection deformation in shield tunnels is studied. Result & Conclusion Factors influencing segment floatation mainly include static buoyancy, dynamic buoyancy, and attitude control. The maximum segment floating occurs between the 5th and 8th rings behind the shield tail. The smaller the longitudinal stiffness, the closer the maximum floating occurs to the shield tail; the larger the longitudinal stiffness, the more the long-range overall heave phenomenon of the tunnel. When the water head height is above the segment top, the segment floating volume will not change with the static water head height, and the floatation caused by static buoyancy does not exceed 30%. The position of the maximum segment floating will not change with the changes in grouting pressure, and the grouting pressure only affects the maximum floating value of the segment, with the maximum floating value linearly correlated with the grouting pressure.

Keywords

• urban rail transit
• shield tunnel
• muddy siltstone stratum
• segment floating value