The doubleOtube(DOT) shield tunnel may undergo longitudinal uneven displacement
due to adjacent constructions. The longitudinal equivalent bending
stiffness(LEBS) stands as a pivotal mechanical parameter, delineating the
longitudinal bending performance of the tunnel and forecasting its deformation
in response to external loads. To ensure the safety of the DOT shield tunnel
structure and predict its longitudinal stress and deformation, the analytical
solution for the LEBS is deduced based on the longitudinal equivalent
continuous model. This model considers the pretightening force of the bolts and
the influential range of the circumferential seam. In addition, expressions for
boundary bending moments are provided under conditions where the neutral axis
is located at the upper edge, upper double arch, waist, and lower double arch.
A case study on the first DOT shield tunnel in China is conducted to analyze
the effects of the bending moment, pretightening force of bolts, and
influential range of the circumferential seam on longitudinal bending
performance. Key findings include: (1) Under the pretightening force of bolts,
the LEBS decreases in a "reverse S" shape with increasing external
bending moment, ultimately approaching that without pretightening force. (2)
The neutral axis position varies and gradually moves downward with increasing
bending moment. When the external bending moment is smaller than the activating
bending moment of the circumferential seam, the LEBS aligns with that of a
homogeneous tunnel. (3) The neutral axis position remains unchanged for an
influential coefficient of the circumferential seam length less than 1. Still,
the efficiency of the LEBS rapidly decreases with an increasing coefficient of
the circumferential seam action zone. When the influential coefficient is
greater than 1, the neutral axis moves upward, and the compression range of the
segmental ring increases. However, the efficiency of the LEBS slowly decreases
and tends toward a certain value with an increasing coefficient of the
circumferential seam action zone. (4) Increasing the pretightening force of
bolts raises the activating bending moment of the circumferential seam, leading
to a slower decay in the LEBS of the tunnel. Simultaneously, the neutral axis
position continuously moves upward, and the compression range of the segmental
ring further expands.
