## 1 Introduction  
GEM is used extensively as an impervious structure in the construction of channels, embankments, dams, reservoir pans, earth and rock cofferdams and water transmission/traffic tunnels because of its flexibility, impermeability, simplicity of construction, easy repairment and cheapness [1, 2, 3]. Since GEM was introduced in the 1980s, it has rapidly become one of the most important construction materials in civil engineering; the critical technical problems tackled with research, innovative construction equipment/methods and improved production process all contribute to the development of GEM. Although there is some progress in the application of GEM seepage control technology, there are still some constraints, such as the current design specifications [4, 5] restricting the application of GEM seepage control in medium and high dams; the safety and service life of the thinner (\(\leq\)1.0 mm) GEM are met with skepticism to some extent, etc. [6]; the limitations of the current evaluation for GEM performance; and the complexity of engineering construction. In addition, the scientific research on GEM seepage control and drainage technology in China primarily focuses on the summary of engineering experience. The GEM is an organic polymeric material, typically divided into polyethylene, poly (vinyl chloride) and rubber. The polyethylene widely applied in China mainly includes polyethylene membrane (PE), high-density polyethylene membrane (HDPE) and low-density polyethylene membrane (LDPE), whereas rubber is mainly thermoplastic polyolefin (TPO), and poly (vinyl chloride) is mainly soft PVC, and GEM at home and abroad is selectively combined with engineering experience and development, for example, Europe and the United States choose the majority of PVC [7]. Initially, PVC GEM was mainly applied in China, but it gradually replaced by PE/HDPE membrane [8]. In recent years, PVC GEM has been adopted as an impervious material in medium-high dams and dams in deep overburden layer. According to the incomplete statistics by International Committee on Dams in 2010, of 216 large earth-rock fill dams adopting GEM as impervious structure in the world, the number of PVC membrane selected is 143, accounting for approximately 60.3% of the membrane impervious dams, while some dams adopt exposed PVC membrane to prevent seepage [9; 10; 11]. PVC GEM still has good flexibility at low temperatures by adjusting the plasticizer type and percentage content, and PE/HDPE GEM fails to maintain the flexibility as that at normal temperatures. The increase in material thickness reduces the flexibility of PE/HDPE, but it has little effect on the flexibility of PVC GEM. Therefore, the widespread use of PVC stems from its strong adaptability to large deformation and good durability. The research results showed that the principal factor responsible for affecting the mechanical properties of polymer material is the temperature [12; 13; 14; 15], and the mechanical properties of GEM present as polymer macroscopical movement, while temperature represents the intensity of molecular motion, and the material exhibits different mechanical properties macroscopically at different ambient temperatures. He, [PERSON] [16] showed that the time for the response of strain of GEM to external force depended on the ambient temperature and decreases with the increasing temperature. [PERSON] [17] suggested that the creep deformation of GEM in the short term at ambient and low temperatures was principally temperature-dependent. [PERSON] et al. [18] studied the mechanical properties of PVC membrane at low temperatures. [PERSON], [PERSON] et al. [19] tested the rupture strength of PVC GEM joint at 0.6 \({}^{\circ}\)C in the field, which was significantly higher than the value in laboratory. [PERSON], [PERSON] et al. [20] found that the flexibility of GEM decreased and the britteness increased at low temperatures.