## 1 Introduction  
The mountain tunnel drainage system is a critical structure used to drain groundwater behind the lining. However, a growing number of mountain tunnels are experiencing a problem: the drainage systems encountered crystalline blockages [1; 2; 3; 4; 5; 6]. Crystalline blockages in mountain tunnel drainage systems refer to the accumulation of mineral deposits such as calcium carbonate in the drainage pipes, which can reduce or completely block the flow of water. The accumulation of mineral deposits in mountain tunnel drainage systems can lead to a range of environmental problems, including flooding, erosion, and damage to infrastructure. As such, it is important to monitor and manage mountain tunnel drainage systems to minimize the impact of crystalline blockages on the environment. Regarding this problem, relevant researchers have carried out a lot of research. The research objects primarily focused on four aspects: groundwater, concrete materials, drainage facilities, and cleaning measures. For example, [PERSON] [7] studied the influence of different slopes of horizontal and vertical drainage pipes and water flow on the rate of crystal formation through an indoor water cycle model test. This research found that the drainage pipe was more effective at preventing the formation of crystals with the increase of the slope of the drainage pipe. At the same time, it was also proposed to apply high-performance scale inhibitors to clean the crystals. Through indoor model tests, [PERSON] et al. [8] explored the influence of concrete materials and groundwater on the formation of carbonate crystals and concluded that the main source of calcium in calcium carbonate is the primary support shotcrete and the amount and rate of crystal construction will be higher if the groundwater is rich in bicarbonate. [PERSON] et al. [9] investigated several tunnels with calcium carbonate crystals in France, analyzed the problem tunnels in France based on the geological image method, and found that the precipitation of calcium carbonate depends on the permeability coefficient of the surrounding rock, the content of calcite, the properties of the lining materials, and the geometry of the tunnel. As far as the treatment plan is concerned, the recommendation is to place the detachable geotextile on the surface of the drain and replace it regularly. [PERSON] et al. [10] found that the formation of precipitates in the drainage pipe was mostly caused by the deterioration and degradation of the tunnel concrete lining by investigating the drainage pipe blockage problem of the Namsan 3 tunnel in Seoul, South Korea. Moreover, quantum rods and magnetization devices were proposed to treat crystals in the drainage pipe. By investigating the Koralm tunnel in Austria, [PERSON] et al. [11] found that the main reasons for the crystallization blockage of the drainage system are the dissolution of cement minerals in concrete and mortar, defects in the design and construction of the drainage system, and rough construction technology. The above research results show that the factors affecting the crystallization blockage of the drainage system of mountain tunnels are multifaceted, and not determined by a single factor. Several factors can influence the crystalline blockage in mountain tunnel drainage systems, mainly including the water quality, geological environment, construction materials, and tunnel design. However, few studies focused on the degree of influence of these factors, which makes it impossible for relevant researchers to grasp the key issues of the crystallization blockage of the drainage system of mountain tunnels. There is a need for more research on the influence of these factors on crystalline blockages in mountain tunnel drainage systems because the problem is becoming increasingly common, and its impact on the environment can be significant.