Abstract: In order to study the nonlinear mechanical properties of the joint stiffness with bolt-concave and convex tenon type in the longitudinal calculation model of shield tunnel, the calculation models of the annular joints under the opening mode and the dislocation mode are established respectively. By analyzing the mechanical characteristics of the joints under different deformation conditions, the nonlinear laws of tensile and shear stiffness of the joints are obtained. The calculation model of shield tunnel longitudinal settlement based on three-dimensional entity-nonlinear spring element is constructed by using nonlinear tensile and shear spring simulation of annular joint; and the model is used to evaluate the influence of surface overload on the safety of segment structure in coastal area of Xiamen Metro Line No. 2. The results show that for the shield tunnel of which the outer diameter is 6.7 m, the inner diameter is 6 m, the ring width is 1.5 m, and the annular joint is connected with M30 bolts: (1) When the opening of the annular joint exceeds 1.78 mm, the tensile stiffness of the joint decreases to 1% of the designed value; and when the opening of the joint exceeds 10.2 mm, the tensile failure can be considered. (2) The shear stiffness is almost unchanged when the amount of dislocation is less than 6 mm, and the shear stiffness decreases to about 25% of the designed value when the amount of dislocation is over 9.7 mm; when the amount of dislocation is over 30 mm, the shear failure can be considered. (3) When the overloading range of the tunnel axis is d, the longitudinal deformation of the segment is affected by ±3d, and the differential settlement of the 50-ring segment of the tunnel axis is less than 23 mm, the curvature radius is not less than 15 000 m.

Key words: shield tunnel, annular joint, nonlinear spring, controlling indicators