Abstract: To examine the mechanical response of a metro shield tunnel during the construction of a cross-passage using the front-traction pipe jacking method, a finite element model based on a Beijing metro shield tunnel is established to simulate the construction process. The model′s accuracy is validated by comparing simulation results with field monitoring data. The effects of cross-passage construction on the dislocations between rings, stress and deformation of special segments, and bolt force are studied. Meanwhile, the effect of different reaction modes on the mechanical characteristics of shield tunnel are analyzed. Key findings include the following. (1) Opening a special segment significantly affects the mechanical properties of the shield tunnel; the stress and deformation increase gradually with the excavation of the cross-passage. (2) The maximum displacement between segments is recorded as 1.17 mm, occurring at the bottom of the joint between the special and ordinary segments. The highest tensile stress in the special segment is 18.6 MPa at the top and bottom of the opening, whereas the maximum compressive stress is 27.0 MPa at the waist of the opening. The maximum transverse expansion and vertical convergence displacement of the special segment are 2.13 and 4.56 mm, respectively, with the inter-ring bolt experiencing a maximum tensile stress of 213 MPa. (3) The backthrust reaction mode proves more effective in controlling the horizontal and vertical displacement at the opening, whereas the front-traction reaction mode better manages the stress and deformation of the segment and the dislocation between rings opposite the opening.

Key words: metro shield tunnel, cross passage, front-traction pipe jacking method; mechanical method, mechanical property