Mechanical response of tunnel structure to hole-breaking process of cross passage pipe jacking construction

To investigate the influence mechanism of the hole-breaking process at the launching stage of pipe jacking on the mechanical response of the main tunnel structure, a three-dimensional simulation model for pipe jacking construction of the cross passage was established based on the construction project of the cross passage in Zhengzhou Metro Line 12. The accuracy of the established model was verified by comparison with field monitoring data. The effects of the hole-breaking construction during the launching stage of pipe jacking on the deformation of the main tunnel segments, internal forces, and bolt stress were studied. The evolution of the mechanical response of the main tunnel structure during the hole-breaking construction process was systematically analyzed. Research results show that the hole-breaking construction causes significantly greater disturbance in the circumferential direction of the segments than in the longitudinal direction, and the disturbance range extends approximately twice the diameter of the main tunnel on both sides of the opening. The 90° position of the semi-cutting ring is most affected by the hole-breaking construction. A distinct tensile stress zone is formed on its outer arc surface, with a maximum tensile stress of 9 MPa. The steel-concrete composite segment at this location ensures structural safety. The internal support system reduces the external soil and water pressure on the main tunnel, effectively lowering internal forces and deformation of the segments. As the segment cutting thickness increases, the transverse elliptical deformation of the lining ring gradually increases, and the bolt stress increases. Circumferential bolt stress is significantly higher than longitudinal bolt stress and approaches the yield strength. Internal forces at the upper and lower ends of the opening dramatically decrease, creating a pronounced cantilever effect. The lost load is transferred to less damaged adjacent ring through longitudinal bolts, leading to a significant increase in internal forces at the 90° position of the semi-cutting ring. This redistribution of internal force mainly occurs during the stage of cutting 3/4 of the segment thickness. The results provide important evidence for revealing the influence mechanism of the hole-breaking process in cross passage pipe jacking construction on the mechanical response of the main tunnel structure. The results also offer theoretical reference for the design and construction of similar projects in the future.