Three-dimensional mechanical analysis model and verification of shield tunnels with double-layer linings

Based on the existing beam-spring model for double-layer lining structures, an improved three-dimensional shell-spring mechanical analysis model for double-layer lining shield tunnel is proposed. This model simulates the mechanical interaction on the interface of the double-layer linings using the compression rod-spring combination method, and fully considers the discontinuous effects of the structural stiffness along the ring and longitudinal distribution caused by the joints of the shield tunnel segments. Based on the modeling and calculation analysis of the Wuhan Metro Line 8 cross-river tunnel project, the calculated internal forces are compared with the measured ones. The comparison shows certain consistency between them, verifying the accuracy and applicability of the three-dimensional mechanical analysis model for double-layer lining shield tunnels. The results show that the distribution of the internal forces of the segment has obvious discontinuity due to the effect of the annular seam and the longitudinal seam, and due to the uneven lithology of the formation, and the bending moments of the upper and lower parts of the segment also differ greatly. If the construction of the secondary linings is performed after the stability of the segment, the internal forces of the segment itself change little, and the secondary linings are mainly affected by their own weight. The internal force distribution exhibits the distribution pattern of "small above and large below," and its magnitude is smaller than that of the segment. It only plays a supporting role in the initial stage of construction.