Investigation of Long-Term Waterproof Performance and Hardness Change of EPDM Rubber Gasket Used for Shield Tunnels

The waterproof performance of shield-tunnel gaskets determines the long-term operation of shield tunnels. To study the long-term waterproofing performance of shield-tunnel gaskets, first, high-temperature aging tests of ethylene-propylene-diene monomer (EPDM) rubber specimens were performed, and an EPDM rubber aging model was constructed based on the Arrhenius equation using the time-temperature equivalence principle. Uniaxial compression tests were then conducted on the EPDM rubber with different degrees of aging to analyze the changes in material parameters C1 and C2 of the rubber intrinsic model with time. Subsequently, a rubber gasket used in a shield tunnel in Nanjing was used as the sample material, and aging tests were conducted on the inner and outer channel gaskets considering different joint displacements. The test results were combined with the p-T-t ternary model based on the Arrhenius equation to predict the 100-year waterproof performance of the shield-tunnel gasket. The results show that the final stress relaxation coefficients of EPDM rubber for 100 years are 0.65 and 0.44 for initial compressive stresses of 1.1 and 1.6 MPa, respectively, as predicted by the aging coefficient model. Furthermore, a clear relationship was observed between the C1 and C2 parameters in the Mooney-Rivlin rubber constitutive model, and the hardness and modulus of elasticity of the rubber material gradually increased over time. The short-term stress relaxation in the early stage of the inner and outer channel gaskets under different openings amounted to approximately 20%-30% of the total relaxation, and the chemical stress relaxation in the later stage accounted for approximately 70%-80%.