## 3 Laboratory Experiment  
### Grouting Ratio Experiment  
A single liquid cement slurry grouting method was adopted for the grouting ratio test, including the grouting method of mainly using cement materials, mixing water into slurry, and injecting single liquid into rock and soil layer. The raw material of the test slurry was 425 ordinary Portland cement. To study the variation law of cement slurry performance under different water-cement ratios, the water-cement ratios in the test were 0.4, 0.6, 0.8, and 1. According to the standard for test methods of concrete physical and mechanical properties (GB/T50081-2019) [33], the cylinder sample was prepared. The corresponding proportion of cement and water were put into the mixing bucket and mixed manually. The mixture with the mold and tamp was filled manually. After tamping, the mold top cover was installed and the test piece was manually pressurized into a cylindrical specimen with a height of 100 mm and a diameter of 50 mm. After standing for 30 min at room temperature, the specimen was demolded. The error of specimen height and diameter was controlled within 0.3 mm, the maximum error of non-parallelism of both ends of the specimen was controlled within 0.05 mm, the end surface was perpendicular to the axis, and the maximum error did not exceed 0.25 mm. The samples were cured for 7 days around 20 \({}^{\circ}\)C under natural drying conditions. Figure 3 shows the sample. To provide a reasonable grouting ratio for tunnel grouting construction and to obtain a better grouting reinforcement effect, the grouting reinforcement effect was evaluated under different water-cement ratios on the basis of the slurry fluidity, setting time, bleeding rate, and strength of the sample. The fluidity of the slurry reflected the viscosity of the slurry. The greater the viscosity, the longer it took to inject into a certain position of the soil. The lower the viscosity, the stronger the fluidity of the slurry, and the grouting time can be shortened during the grouting process and the grouting efficiency can be improved. Figure 4 shows the fluidity test results of cement slurry. The viscosity of cement slurry decreased with the increasing water-cement ratio. When the water-cement ratio increased from 0.6 to 1, the initial viscosity of cement slurry decreased from 9.6 s to 8.48 s, which is a decrease of 1.12 s. At 30 min, the viscosity decreased from 10.01 s to 8.48 s, which is a decrease of 1.53 s. The 60 min viscosity  
Figure 2: Cross-section of double-arch tunnel (unit: cm). decreased from 10.8 s to 8.49 s, which is a decrease of 2.31 s. Additionally, the viscosity of cement slurry increased gradually under different water-cement ratio; the smaller the water-cement ratio was, the faster the viscosity increased. When the water-cement ratio was 1, the viscosity remained basically unchanged with time. Figure 5 shows the relationship between water-cement ratio and initial setting time. The initial setting time of cement slurry basically increased linearly with the increasing water-cement ratio. When the water-cement ratio was 0.4, the initial setting time of cement slurry was 318 min, and when the water-cement ratio increased to 1.0, the initial setting  
Figure 4: Fluidity test results of different water–cement ratios. Figure 3: Test sample. time increased to 696 min, an increase of about 1.2 times. According to the test results, the relationship between water-cement ratio and initial setting time of cement slurry was fitted, and the following was obtained:  
\[\text{y }=\ 630\eta+39, \tag{1}\]  
where y refers to the initial setting time of cement slurry (min) and \(\eta\) refers to the water-cement ratio of water slurry. The correlation coefficient R\({}^{2}\) of the fitting result was 0.9997, which shows that the fitting result was good. Cement and water were fully mixed to form a cement slurry. After standing for a period of time, a part of free water precipitated out of it. The phenomenon is called bleeding, which is related to the stability of the slurry.