Research On Bearing Performance Of Steel Plate Reinforced Shield Tunnel Segmental Lining And The Degradation Law Exposing To Elevated Temperatures

For shield tunnels whose transverse convergence exceeds the code requirements while still limited by the tunnel construction boundary,the bonded steel plate strengthening method is being promoted and applied gradually.Due to a series of unexpected accidents such as the short circuit of an electric circuit,equipment failure and artificial arson,shield tunnel reinforced by bonded steel plate may suffer from partially elevated temperature,resulting in the subsequent bearing performance of the shield tunnel being weakened or even structural safety being threatened.To this end,this paper has implemented the full-scale bearing capacity test on shield tunnel joints strengthened by steel plates exposing to elevated temperatures,the model test on the single ring of strengthened shield tunnel segments considering the failure of structural adhesives,and also the detailed numerical calculation to simulate the actual embodied responses.Further,this paper discussed the quantitative relationship between the failure range of the structural adhesive of the steel plate strengthened segment structure exposing to partially elevated temperatures,the decrease of the strengthening potency of the bonded steel plate,and the residual bearing capacity of the segment structure.The key content and research results are summarized as follows.(1)By the manufacturing of assembled segmental joints,the structural bearing capacity of the full-scale segmental joints strengthened with bonded steel plates exposing to elevated temperatures was tested and discussed.Primary results have stated that comparing to the unstrengthened segmental joints,the equivalent bearing capacity of the steel plate strengthened segmental joints without encountering elevated temperatures is 2.61 times higher,but after being exposed to elevated temperature,the equivalent bearing capacity dropped to1.89 times higher.The elevated temperatures have led to the failure of the bonding surface and the weakening of strengthening potency.Generally,the failure of the epoxy resin adhesive bonding leads to the separation of the steel plate and the inner surface of the segment.The research results could be provided as references to determine the decreasing strengthening potency at elevated temperatures.(2)Considering the failure degree and failure range of the structural adhesive,a total of 12 groups of steel plate strengthened single-ring segments model tests were conducted.The test results show that the equivalent bearing capacity of the full-circumferential strengthened segmental structure is increased by 1.59 times.When structural adhesive fails 25%,its equivalent bearing capacity is increased by 1.29 times;Failing 50%,its equivalent bearing capacity is increased by 1.08 times;Failing 75%,its equivalent bearing capacity is increased by only 1.04 times.The adverse effect on strengthening potency of the structural adhesives failure ranges is in such a descending order: the vault,the waist and the bottom.The research results could be provided as references for the maintainance of steel plate strengthened shield tunnels(3)For the above two sets of tests,a detailed finite element model interpreting analysis was carried out.The model carefully describes the segmental details,including the hand hole,the bolt,the watertight gasket,the bonding surface,the steel plates,et al.The test results from both the experiments are promisingly interpreted by the numerical model and it is believed that the simulation is reliable for understanding the mechanical and deforming properties.