# Waterproof Performance of Sealing Gasket in Shield Tunnel: A Review
## 2 Mechanical Behavior of Lining Structure and Joints
### Waterproof Performance Deterioration of Tunnel  
With the deepening understanding of the leaking mechanism, scholars devote themselves to the research of tunnel waterproof performance deterioration. In terms of laboratory test technologies and deterioration simulations, [PERSON] et al. [14] carried out investigations and numerical simulations on gasket sealant behavior under high hydrostatic water pressure and a relationship between joint deformation; waterproof performance was obtained and a waterproof performance assessing method was proposed. [PERSON] et al. [15,16] carried out joint waterproof performance tests for full-scale segments and reduced-scale specimens after fire damage. From this, the temperature distributions and the gasket deterioration pattern under high temperatures were acquired. [PERSON] et al. [17] and [PERSON] et al. [18] studied the influences of the mechanism of joint opening and offset of subway tunnels on the waterproof performance of gaskets, and corresponding indoor tests were carried out. Aiming at the test characterization of waterproof capacity or seepage water pressure of tunnel joints, the behavior of seepage water under sand leakage conditions is not mentioned by the aforementioned contributions. [PERSON] et al. [19] established a Coupled Eulerian-Lagrange-based model and the whole leakage process at the segmental joints, considering large deformation and seepage flow in the contact surface, was simulated, and the validity of the hydro-mechanical model was verified. [PERSON] et al. [20,21] designed a test apparatus to simulate the soil and water losses under the condition of a large joint opening, and an analysis based on the sandy soil of the Tianjin Metro Tunnel was carried out. Given the working conditions of Southern California and Southern China with high seismic intensity, [PERSON] et al. [22,23] and [PERSON] et al. [24] conducted joint waterproof performance tests under reciprocating loading conditions, hence, the waterproof capability under vibration was obtained. [PERSON] et al. [25] investigated the influence mechanism of joint rotation on waterproof capacity; methods were proposed to mitigate the joint leaking situations. [PERSON] et al. [26,27] developed a waterproof performance testing technology for full-scale segment joints, and impacts of constructing loads on the deformation of gaskets were tested.  
Figure 1: Joint waterproof sealing diagram of shield tunnel: (**a**) lining structure, (**b**) joints [13] (Reprinting with permission from [PERSON] et al., 2019), (**c**) water pressure expansion process, (**d**) joint gaskets [7] (Reprinting with permission from [PERSON] et al., 2018).  
With the development of computer sciences and designing protocols, novel technologies and structure forms are introduced for the detection and prevention of the waterproof performance deterioration of joints. Based on a convolutional neural network and EfficientNet, [PERSON] et al. (2018) proposed a defect detecting model, which can be implemented to detect localized leakage in tunnels and monitor the working conditions throughout the design service life (Figure 2). The waterproof performance of a novel structure type with double-layer sealing gaskets at intervals outside the bolt was tested by [PERSON] et al. (2019), and the results indicated that the novel structure can substantially enhance the waterproof capacity.  
Per the literature review, existing research on waterproof performance deterioration captured numerous undermining factors, e.g., high hydrostatic water pressure, high temperature caused by fire, sandy leakage, seismic load, and deformation of the segmental rings. New testing technologies were introduced, and novel structures and waterproof performance evaluation methods were introduced to address the challenges.