Correlating the time-dependent behavior of EPDM gaskets with the long-term sealant performance of gasketed joints in shield tunnels

This paper proposed a novel theoretical model to evaluate the long-term sealant performance of gasketed joints, where different time-dependent behaviors of EPDM (ethylene propylene diene monomer), were considered. First, the time-dependent behaviors were determined through aging tests, numerical modeling, and AFM (atomic force microscopy) tests. Rubber hardening was derived as an equivalent modulus using the Mooney-Rivlin model, while the Arrhenius formula was applied to the test data of elongation at break to characterize the effect of rubber degradation. The EPDM surface morphology was characterized by the fractal dimension and RMS (root mean square) -slope. They were subsequently utilized to derive the percolation pressure, whereby the impact of surface roughness was evaluated. In addition, the existence of expel pressure was verified via contact angle tests. A long-term theoretical model was established by incorporating time-dependent behaviors and expel pressure, which was verified by testing data. Based on the time-temperature superposition, the sealant performance of gasketed joints in a 100-year service duration can be obtained. The results indicate that the waterproof capacity drops from 1.69 to 0.16 MPa in 100 years when the opening is 7 mm. Rubber hardening enhances both the confining and percolation pressures. Rubber degradation effect has the largest adverse impact on sealant performance, while the percolation pressure is responsible for the ‘not waterproof’ region, implying that the gasketed joints may have lost all their waterproof capacity before fulfilling a 100-year duration in conditions of large openings and long-term use.