## 1 Introduction  
The construction and development of railway tunnels in China have a history spanning more than 130 years. In the past 40 years of China's reform, more than 12,000 tunnels have been built, with a total length of about 17,000 km (90% of the total length of China's railway tunnels). Among them, 2262 railway tunnels were built during the \"Eleventh Five-Year Plan\", with a total length of about 2686 km (the proportion is 14%). A total of 3611 railway tunnels were built during the \"Twelfth Five-Year Plan\", with an entire length of about 6038 km (the proportion is 31%). A total of 3387 railway tunnels were built during the \"Thirteenth Five-Year Plan\", with an overall length of about 6592 km (the proportion is 33%) [1]. With the continuous development and construction of the railway, train speeds are gradually increasing, the density is increasing, the total weight is increasing, and the disease of mud pumping and mud pumping at the tunnel base is becoming more and more prominent. In the process of railway tunnel construction, new engineering problems have emerged that need to be solved. Mud pumping will destroy the railway subgrade, which will not only affect the service life of the tunnel but also endanger the safety of railway transportation [2; 3; 4]. [PERSON] investigated the disease of the Datong-Pu line of the Datong-Qinhuangdao line and found that almost every section of the Beitongpu line has the disease point of subgrade mud pumping. In the turnout, rail joint, and uphill section, obvious subgrade mud can be found on the surface gravel after rainfall [5; 6]. The K100-K294 section of the Baolan line passes through the Yellow River irrigation area. In the spring melting season, the frozen subgrade soil melts to form mud and rises upward. The length of the section where mud pumping and roadbed sinking occur is as long as 13.5 km [7]. The 2013 autumn inspection report of the Railway Corporation (former Ministry of Railways) shows that the total length of the roadbed is 144,000 km and the length of the slurry section is 5805 km. The distribution range is extensive, and the disease develops rapidly. According to the statistical data of Shuohuang Railway in 2008, there were 882 areas affected by mud pumping, which seriously affected the capacity expansion and traffic safety of the heavy haul railway [8]. The mud pumping disease along the Dabashan tunnel accounts for nearly 10% of the total length of the tunnel [9]. Given the increasingly prominent problem of mud pumping disease, many scholars and engineers have actively invested in research [10; 11; 12]. Under the condition that the Bozhai No. 2 Tunnel of the Xianggui Line was built many years ago, after the implementation of the speed-up plan of the trains, the mud pumping in some sections has developed rapidly. [PERSON] [13] proposed a new type of drainage ditch to improve the mud pumping in the base by adopting the bottom cover ditch. [PERSON] et al. [14] also put forward corresponding measures to increase the base grouting due to the speed increase of the trains and applied this remediation scheme to a tunnel project on the Beijing-Kowloon line. Through on-site statistical investigation and analysis, [PERSON] [15] put forward several constructive suggestions for the related diseases of loess tunnels. [PERSON] [16] proposed five kinds of treatment measures for steel sheet piles according to different settlement amounts for the deformation of the foundation caused by mud pumping in the loess tunnel foundation. [PERSON] [17] summarized the characteristics of highway loess tunnel diseases and put forward the construction principle of combining water control, strengthening support, and detection. [PERSON] et al. [18] studied the evolution mechanism of lining cracking caused by mud pumping in loess tunnels and finally put forward the measures of root pile and rammed pile reinforcement.