###### Abstract  
In order to solve the problem that the hole-forming rate of boreholes is low and it is difficult to reach the designed length when supporting a long pipe shed in loose stratum in a shallow buried section of a long-span tunnel, it is necessary to pre-reinforce the loose stratum in order to improve the strength and integrity of the surrounding rock. Relying on the grouting project of the shallow buried section at the exit of Botanggou tunnel, it is assumed that the grouting material is Newtonian fluid and the steel floral tube shows cylindrical infiltration and diffusion. Through the analysis of the structural characteristics of the injected stratum, the conceptual model of infiltration grouting is established. Twelve groups of test slurry were prepared with ordinary Portland cement and ultra-fine cement, and through the analysis of the slurry parameters of each group, ordinary Portland cement slurry was selected with a water-cement ratio of 1:1 plus 3% water glass to strengthen the gravel layer, and ultra-fine cement slurry with a water-cement ratio of 1:1 plus 3% water glass and 0.3% polycarboxylate superplasticizer to strengthen the fully and strongly weathered porphyritic granite layer. Through the on-site single-hole grouting test and combining with the empirical formula, the maximum diffusion radius of single-hole infiltration grouting is calculated, and the sliding width of the sidewall is deduced using Terzaghi theory. To ensure the grouting effect, the 5 m expansion of the excavation profile is taken as the grouting range. Grouting construction adopts the overall order of periphery and then interior, and three-sequence opening and grouting are adopted in the same row of grouting holes, which can effectively prevent grouting running and grouting. For the strata treated by surface grouting, the construction of the long pipe shed is smooth and reaches the designed length, and there is no large deformation of the surrounding rock when excavated using the CD method. The treatment effect is analyzed by the P-Q-t control method, excavation observation method, and deformation monitoring method. The results show that the injected stratum is fully infiltrated and gelled, forms an obvious grouting stone body, the integrity and strength of surrounding rock are obviously improved, and the convergence values of the tunnel surface, vault subsidence, and clearance do not exceed the alarm value of 60 mm. The research results provide some awareness and understanding of the grouting pre-reinforcement of loose stratum in a shallow buried section of a long-span tunnel in the future. t 2022 2022 2  
of side walls, ground subsidence, and even roof fall, bringing great inconvenience to construction and seriously threatening the safety of construction personnel [1; 2; 3; 4; 5; 6]. How to pass the shallow buried section of a long-span tunnel safely, economically, and quickly has become a major subject for domestic and foreign engineers and technicians [5; 6; 7; 8; 9; 10; 11]. At present, the most common measure is to use the pipe shed pre-support to control the excavation deformation of the shallow buried section of the tunnel, so as to ensure safe entering and smooth tunneling. However, the hole-forming rate of boreholes is low and it is difficult to reach the designed length. Therefore, tunnel builders have been working hard to find another stratum pre-reinforcement measure to address the issue. In some projects, the surface grouting method has been tried to pre-reinforce the loose stratum in the shallow buried section to cooperate with the pipe shed forming. The surface grouting pre-reinforcement method is used to inject cementitious materials into the cracks or holes of rock-soil mass under a certain grouting pressure. Then, a series of measures are taken to fill, infiltrate, compact, and split the injected rock-soil mass so that the particles or blocks are connected with each other.