Abstract: The construction of the dual-direction eight-lane open-cut tunnel on Xinsen avenue in Chongqing, China, faces several challenges, including slow progress, difficulties in precision control, and high construction costs. To address these issues, an innovative inverted T-shaped self-stabilizing composite joint is designed and developed. Field tests are conducted to verify the load-bearing capacity and reliability of the joint. Long-term monitoring is implemented to evaluate the stress and strain in the concrete and steel reinforcement, as well as the relative rotation and deformation of the joint, in comparison to fully prefabricated joints. The findings are as follows: (1) Backfilling above the arch and extended use significantly affect structural performance. Notably, the adverse effects of early-stage backfilling on the composite joints diminish over time, allowing a transition from localized to full-section compression and thereby enhancing structural stability. (2) The incorporation of annular reinforcement in the post-cast region of the inverted T-shaped joint improves stress distribution in the compression zone, thereby enhancing load-bearing capacity. (3) Monitoring data indicate that although the deformation trends of the self-stabilizing composite joint resemble those of fully prefabricated joints, the magnitudes are smaller, resulting in improved load performance. These results demonstrate that the self-stabilizing composite joint structure offers notable advantages in improving construction efficiency, reducing precision requirements, and ensuring reliable arch-top connections.

Key words: large-span open-cut tunnel, prefabricated arch structure, self-stabilizing composite joint, field test