# Waterproof Performance of Sealing Gasket in Shield Tunnel: A Review
## 3 Rubber Material Characteristics
### Structural Characteristics and Durability  
In the indoor segment joint full-scale test, it was found that with high rubber hardness, the closure stress will exceed the shear strength of the concrete groove and cause shear failure at the joint closure stage, which leads to concrete burst in segments [44; 45]. Targeting the engineering problems mentioned above, recent studies have been focusing on optimizing the cross-section of the gasket to control its closure stress. [PERSON] et al. [46] discussed the influences of the Balloon Effect on the compressional performance of the internal closed cavity; the results indicated that due to the presence of pressure in the internal holes, the buckling process of gasket hole wall lags was obvious, and the closure stress increased by over 10%. [PERSON] et al. [47] investigated the effect of the internal hole layout and constitutive model, and corresponding simulation results showed great influences of coefficient C\({}_{10}\) and the internal hole layout on the average contact stress. In addition to in-depth research on the mechanical properties of joint gaskets at room temperature, some scholars [15; 37; 48] showed interest in the material property damage of joint gaskets in high-temperature scenarios.  
On the other hand, regarding the durability of tunnel joint gaskets during the service period, [PERSON] [49] pointed out the significant effect of the durability of segment joint waterproof materials on the long-term safety and functionality of tunnels. Taking the Shanghai Chongming Yangtze River tunnel as the engineering case, [PERSON] et al. [50] carried out the artificially accelerated aging test of EPDM gaskets and predicted the contact stress of joint gaskets after simulating 100-year aging. [PERSON] et al. [51] studied the long-term performance of EPDM gaskets under constant compression for the Quintang River tunnel. Further, [PERSON] et al. [52] proposed a hyper-elastic time-varying constitutive model of EPDM material suitable for the water environment by conducting tensile tests of EPDM dumbbell-type specimens based on the theory of large deformation of elastomer [53] and its extended theory [54]. [PERSON] et al. [55] carried out a full-scale parametric study on the design parameters of the gasket and its influences on the waterproof performance, and the fluid pressure penetration (FPP) module of the FE commercial package ABAQUS/Explicit was implemented to simulate the seepage process of segmental joint leakage. In addition to that, [PERSON] et al. [33] summarized the material characteristics of joint gaskets in shield tunnels.  
Scholars have conducted productive studies on the mechanical properties and durability prediction of joint gasket materials, and preliminarily explored the degradation of material properties of gaskets. Existing material characteristic research focused on the constitutive model, time-dependent characteristics, structure response, and gasket layouts while a comprehensive solution is yet to be proposed. The layout study is closely related to the constitutive model, which is highly variable with aging. To begin with, a comprehensive investigation and a universal longevity prediction method should be established.