Abstract: Temperature variations of the in-pipe medium in large-diameter steel pipes installed within long-distance shield tunnels can induce excessive thermal deformation and stress, leading to joint deformation, sealing failure, and structural damage. To address this challenge, a thermal load control scheme combining interval-end anchorage and flexible end structures is proposed. Based on the structure-ground load transfer mechanism, a self-compacting concrete anchorage segment is constructed between the steel pipe and shield segments. Longitudinal thermal loads induced in the steel pipe are transferred stepwise to the shield segments through features such as handhole shear keys and further transmitted and dissipated into the surrounding ground via tangential friction between the segments and the surrounding strata, thereby restricting the thermal deformation of the steel pipe and reducing the longitudinal force exerted on the shield working shaft. Consequently, a flexible connection structure is proposed at the tunnel entrance and exit to release the longitudinal restraint imposed by the working shaft on the tunnel section through rubber buffering and compression-based waterproofing details. A three-dimensional refined finite element model is employed to analyze the longitudinal load transfer behavior and structural response characteristics of the end-anchorage zone. The numerical results show that: (1) the end-anchorage method fully utilizes the restraint effect of the ground and significantly reduces the reaction force at the working shaft; and (2) thermal deformation and additional internal forces of the structural system decrease with increasing ground restraint stiffness. The flexible end structure more fully uses the ground restraint without significantly increasing the internal forces of other structural components, while effectively avoiding excessive forces on the working shaft, representing a more thorough solution.

Key words: shield tunnel, penetrating steel pipe, thermal deformation, load transfer, end anchorage, flexible end