Mechanical behavior of Quasi-rectangular segmental tunnel linings: First results from full-scale ring tests

- Quasi-rectangular tunnels combine the advantages of circular and rectangular tunnels.
- Bearing mechanism and failure process are well investigated by full-scale ring test.
- Modified routine method and beam-spring model method all meet design request.
- The tested lining has high loading safety reserves under overburden condition.
- The weakness of the lining is revealed and further optimization should be considered.

The shield driven method is now a preferred choice when urban subway tunnels are constructed. In high density cities, a suitable cross-section for tunnel structures is rather important. In this study, a full-scale ring test is conducted in order to determine the mechanical behavior of Quasi-rectangular segmental tunnel linings, firstly designed and employed in Metro Line 3 in Ningbo, China. The design of experimental specimens and loading processes are introduced. Main results of tests are explored, including the failure state and measurement items, convergence deformation, strain of rebars, bending angle of joints and bolts' strain .The ultimate bearing capacity of the structure is also reached during the test. According to the experimental results, two analysis methods are utilized to evaluate the mechanical behavior of the structure under design condition. The bearing mechanism and weakness of the lining are revealed as well. Safety factor of elastic stage and ultimate stage are also defined to evaluate safety reservation of the structure under unexpected circumstance. The test will lay the foundation for further verification and optimization of Quasi-rectangular segmental tunnel linings.