Airtightness Performance Test and Failure Models for Low-to-Vacuum Maglev Train Tunnel Joints

Abstract

Abstract The airtightness at the joints of segment lining structures is one of the critical problems for low-to-vacuum maglev train tunnels that needs to be addressed. A new apparatus was designed to test the airtightness performance of the gasket-in-groove at longitudinal and circumferential joints. Based on the test results, four mechanical models based on the theory of elastic mechanics were developed to describe the short-term and long-term sealing failure behaviors of longitudinal and circumferential joints, which are subjected to vacuum pressure on one side of the gasket, and the corresponding air-leakage equations for contact interface were also deduced. The test results show (1) a higher initial contact pressure in the gasket-in-groove would result in faster stress relaxation; (2) a greater initial contact pressure would result in better joint sealing; and (3) for the same initial contact pressure, the sealing capacity of longitudinal joints is significantly better than that of circumferential joints. The test results are in good agreement with the models. The developed models can be used to interpret the sealing failure mechanism through the gasket contact pressure path. Moreover, the mechanical models show that the sealing capacity of the circumferential joint gasket is positively correlated with the airtightness coefficient and the gasket equivalent Poisson’s ratio, whereas the sealing capacity of the longitudinal joint gasket is positively correlated with the airtightness coefficient, the gasket equivalent Poisson’s ratio, as well as the tunnel outer diameter, and negatively correlated with the gasket width.