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Mechanical Characterization of Joints in Segmented Tunnel Liners Due to Thrust Jack Loading and Service Loading
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2023-12-01
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[PDF-17.96 MB]
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Edition:Final Report (Oct. 2021 to Dec. 2023)
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Abstract:A full-scale experimental and numerical modeling study is conducted to assess the mechanical performance of tunnel lining segments and their behavior under different loading conditions. This study found that the observed crack and strain development matched well with the expected damage formation from the FEA. The addition of supplementary periphery reinforcement in the hybrid segment resulted in earlier crack formation but provided additional strength against radial bursting failure under overload conditions. This study also found that radial thrust jack load eccentricity of 38 mm towards the extrados surface did not have a significant influence on the cracking performance caused by bursting stress. This study highlights the nonlinear behavior of steel fiber reinforced concrete (SFRC) under thrust demand, which generally appears in the transition zone between lower and upper tensile strain limits. Overall, this study provides insights into the behavior of segmental tunnel lining systems and can inform design and maintenance practices to improve tunnel infrastructure performance and safety. Flexural assessment of radial joint rotational behavior is also conducted. This study finds that the Janssen model, which idealizes joint contact, overestimates the rotational stiffness of closed joints at low axial loads and provides overly conservative estimations of rotational stiffness and flexural capacity at large rotation levels. It is suggested that for a better approximation through computational joint models, factors such as skewness, bolts, gasket, effects of confined concrete, and the relationship between joint contact and axial force levels should be considered. This study also concludes that bolting can provide significant rotational stiffness at large joint rotation levels, and it is suggested to reserve bolts at joint locations that might experience large rotation due to earth pressure and other types of loading. This study also finds that the flexural capacity of skewed radial joints is approximately 70% higher than predicted in Janssen's model when subjected to certain axial loads. Finally, the study finds that damage to the joint at large rotations is limited to hairline cracking of the contact surface, with no visible damage on the intrados under these elevated demands, thus limiting the potential for in-situ inspection. The study also finds that the use of SFRC does not prevent the formation of fire-induced spall of the intrados surface of the tunnel line. Additional work is needed to prevent this mode of failure.
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