# Seismic Isolation Effect of Non-Water Reacted Two-Component Polymeric Material Coating on Tunnels
## 1 Introduction  
The seismic response mitigation and seismic protection of structures have been discussed in recent decades [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. For tunnels, coating with soft seismic isolation materials has been studied by many researchers. The seismic isolation effect of a rectangular-shaped tunnel was investigated by [PERSON] et al. (1999). In their work, the seismic isolation layers were installed in two patterns. An isolation layer wasused around a new tunnel, or the vertical isolation walls were equipped at both sides of an existing tunnel [1]. [PERSON] and [PERSON] (2000), [PERSON] and [PERSON] (2001), and [PERSON] and [PERSON] (2001) showed that materials with a low Poisson's ratio and a low shear modulus were preferable for enhancing the seismic efficiency of an isolation layer. They studied the influence of key material properties, such as the reduction factor (TF\({}_{\text{coat}}\)/TF\({}_{\text{uncoat}}\)), on the seismic isolation effect. TF\({}_{\text{coat}}\) and TF\({}_{\text{uncoat}}\) are the transferring factorsin the cases with and without coating [2; 3; 4]. [PERSON] (2004) combined the 3D finite element method and centrifuge model to demonstrate the effectiveness of the isolation layer and cement solidification surrounding the tunnel [5]. [PERSON] et al. (2012) used a polymer isolation method to reduce the seismic effect on the tunnel, and the influences of shear stiffness and thicknesses of soil covering the tunnel were studied [6]. [PERSON] et al. (2013, 2018) and [PERSON] et al. (2018) retrofitted the tunnel with foamed concrete, andthe subsequent effectiveness of seismic isolation was evaluated by bothnumerical and experimental methods [7; 8; 9]. [PERSON] et al. (2016) investigated the dynamic earth pressure on the tunnel via a shaking table test. They pointed out that when a geo-foam isolation layer was utilized, the earth pressure decreased to 10%-30% of that without a seismic isolation layer [10]. [PERSON] et al. (2018) conducted two dynamic centrifuge tests to demonstrate the isolation effectiveness of rubber under seismic loads. The test results showed that the rubber isolation layer effectively decreased dynamic bending moments for tunnels with various diameters [11]. According to the numerical results of [PERSON] et al. (2019), a significant reduction of axial forces and bending moments of the lining was observed when Expanded Polystyrene Geo-foam was utilized to coat the lining [12]. Furthermore, [PERSON] (2012) went through the investigations and damage features of tunnels after the Wenchuan earthquake, and he concluded that the isolation layers were able to enhance the seismic isolation performance [13]. Implementing an isolation layer is a typical passive seismic isolation method. As mentioned before, the effectiveness of seismic isolation layers using rubber, foamed concrete, asphalt-based grouting materials [14], aluminum foam [15], or polymeric materials has been verified, but these materials have some disadvantages. The strength of rubber is easily affected by changesin temperature and is weak at preventing corrosion. The strength of foam concrete is affected by freezing and thawing when water goes into the fissure of foam concrete, and it lacks the ability to provide consistent compressive strength. Asphalt-based grouting materials are sensitive to temperature [14]. Aluminum foams prone to having slight cracks after cooling due to the characteristics of thermal expansion and cold contraction [15]. According to the work of [PERSON] and [PERSON] (2009), [PERSON] et al. (2011a), [PERSON] et al. (2011b), and [PERSON] (2012), the non-water reacted two-component polymeric material (NRTCPM) is composed ofpolyol and polymethylene polyphenyl isocyanate. When mixed together in a specific proportion, the foamed NRTCPM is formed [18]. This material is more corrosion-resistant than rubber, and can achieve adequate strength earlier than foam concrete [18; 19; 20; 21; 22].