An improved model for shield tunnels with double-layer linings and its application in engineering

An improved model for shield tunnels with double-layer linings is proposed. It can reflect the nonlinear characteristic of bending stiffness of segment joints and the failure mechanism of compression and shear springs between segments and secondary linings. The internal force of linings of Shiziyang tunnel is analyzed using this model. The results show that: (1) The increment of bending stiffness of the segment joints can increase the values of the maximum positive and negative bending moments of the segments, while it has slight effect on the internal force of the secondary linings and the maximum axial force of the segments. (2) The internal force is larger than that in reality if the failure mechanism of springs between segments and secondary linings is not considered in the model. (3) The bending stiffness of joints varies slightly if the structure is situated in uniform strata (t/D=0 or 1, t is the distance from the tunnel top to the stratum interface, D is the diameter of tunnel), while its value varies sharply if the structure is situated in nonuniform strata. (4) The maximum and average forces of compression and shear springs will increase with the increment of t/D.