# Waterproof Performance of Sealing Gasket in Shield Tunnel: A Review
## 1 Introduction  
With the development of the economy and the improvement of people's living standards, aboveground construction in urban areas is nearly saturated, which accelerates the vigorous development of tunnel construction. At the same time, the highway, railway, and subway tunnels, as the main arteries of transportation, are suffering from leaking accidents one after another due to natural or man-made factors, causing deleterious consequences and huge economic losses [1].  
According to China's construction code, the design service life of energy and transportation shield tunnels is usually up to 100 years or even 120 years. Ensuring its safety and functionality during service life under harsh and variable influences [2, 3] has become a severe challenge faced by the majority of engineering scientists. The existing construction and operation experiences of cross-river and sea-crossing tunnels present a situation of widespread leakage [4, 5]. Table 1 lists the representative tunnel leakage accidents.  
The waterproof performance of shield tunnels follows the principle of \"prevention first, rigid and flexible combined, multiple layers of defense, and comprehensive treatment\". The key to it lies in the segment joints [6]. The reinforced concrete segment consists of the majority of the shield tunnel, which excels in permeability resistance, as shown in Figure 1a. It is worth mentioning, however, that the segments can be arranged both in alignment and staggered, in practice. Existing engineering examples show that the waterproof performance of tunnels is controlled by joints (Figure 1b). In the construction stage, the gaskets between the longitudinal joints and the circumferential joints are pressed by shielding jacks to form contact stress and resist the intrusion of external water pressure, as presented in Figure 1c. The mainstream strategy for shield tunnel joints in China is to glue EPDM gaskets onto the outer groove of the segment, which is proved reliable under targeted working conditions. However, with hazardous factors (earthquake, fire, etc.) imposed at a certain magnitude, the gaskets are likely to fail.  
Waterproof failure is a typical continuous-discontinuous hydraulic expansion failing process [7]. Seepage of the gasket contact surface is a process in which the contact surface of the gasket keeps opening and water keeps penetrating under pressure. When the contact surface of the gasket is completely opened, a water seepage path is formed, resulting in the occurrence of joint leakage (Figure 1d). It can be seen, however, that sealing gaskets play a vital role in the segment joint waterproof process.  
Based on the above engineering problems, this paper summarizes the research progress on waterproofing of sealing gaskets, to guide follow-up research and practical referencing for engineering design. Combined with the domestic and foreign scholars' research on the shield tunnel joint sealing performance and analysis methods related topics, in this article, the waterproof performance, material characteristics, numerical simulation, and thermal-mechanical coupling analysis of the shield tunnel joint sealing gasket are discussed.