Bearing capacity and failure behavior of segments with a mid-span opening of a shield subway tunnel

Abstract

This paper investigates the load-bearing properties and failure mechanisms of shield segments with a circular mid-span opening in shield subway tunnels. Two full-scale specimens with opening diameters of 100 and 200 mm were manufactured and tested, revealing that with an increasing opening diameter, the failure mode transferred from uniform tensile fracture of inner arc concrete to the peeling and crushing of the outer arc concrete. Moreover, the loading process can be divided into four stages, i.e. elastic, plastic expansion, failure, and ultimate stages, and each stage shares a critical load. Subsequently, numerical models were established using the elastoplastic damage constitutive of concrete, and its reliability is verified by the experimental results. Afterward, parametric analysis was performed considering the plain concrete loss and reinforced concrete loss. The analysis results show that the plain concrete loss significantly weakens the cracking load of the segment, while reinforced concrete loss has the greatest impact on the failure load. Finally, a comparative analysis is conducted between the bearing characteristics of the local failure segment, standard shield segment, and the segment joint. Overall, the research results can provide a theoretical basis for the field reinforcement and the safety assessment of local failed shield tunnels.

Keywords:

• Bearing capacity
• failure mechanism
• full scale test
• local failure
• parametric analysis
• shield segment
• subway tunnels

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors gratefully acknowledge the financial support provided by Guangdong Provincial Key Laboratory of Intelligent Disaster Prevention and Emergency Technologies for Urban Lifeline Engineering under Grant No. 2022B1212010016, National Natural Science Foundation of China under Grant Nos. 51978019 and 52278382, and Natural Science Foundation of Beijing Municipality under Grant No. 8222004.