## 4 Mechanism of Layered Grouting Reinforcement for Surrounding Rock of Roadway
### Mechanism of Roof Layered Grouting Reinforcement  
Grouting can improve the fracture structure inside the broken coal and rock mass, increase its internal friction angle and cohesion, and enhance the integrity and strength of the surrounding rock of the roadway. Generally, the split grouting method is used. When the pressure of grout is greater than the shear stress of compaction grouting, the coal bed will split and the grout diffusion radius will increase, forming a more extensive range and a more stable overall structure. The splitting surface produced in the grouting process mainly occurs on the stress surface with the lowest resistance to splitting. As shown in Figure 7, the grout vein network formed by fracturing grouting near the borehole can play a role in extrusion and filling. Squeezing the slurry vein to form the slurry vein to reinforce the surrounding coal and rock mass and improve the stability of the surrounding rock of the roadway reinforces the coal and rock mass. According to the previous article's coal seam histogram and test analysis, the roof fracture zone mainly occurs in the roof coal seam and mudstone layer. The plastic zone mainly occurs in the silty fine sand stratum. The silt rock stratum has significant strength and is not damaged; thus, it is suitable for anchoring the end rock stratum. Therefore, it is the key to control the stability of the roadway to strengthen the support of the roadway  
Figure 6: Distribution of roadway surrounding rock state. by using anchor bolts and cables combined with layered grouting to reduce the stress gradient of the roof by layered grouting and improve the self-strength of the rock mass at the same time. The bolt and cable provide active support, and the preload is expanded to increase the vertical stress of the rock stratum. After layered grouting, the stress on the rock stratum is uniform, the stress in the layer is homogeneous, and the stress gradient between layers is reduced so no stress concentration occurs on the roof. At the same time, grouting also increases the cohesion and internal friction angle of the rock mass, reducing its destructive capacity. As shown in Figure 8, after the roadway excavation, the early setting and early strength grouting fluid is used to support the \"shallow\" part of the roadway roof so the \"shallow\" broken coal body can quickly form a rock stratum with a particular strength. At the same time, the internal stress environment is changed by a specific preload, and the stress gradient between rock layers is reduced. Then, the \"deep\" grouting cable grouting is carried out, and the superfine cement grouting material uses its good fluidity and permeability to make the \"deep\" fissure-developed coal. Rock masses form a complete rock stratum with long-term stability. After grouting, the roof forms a relatively complete rock stratification, and the \"shallow\" and \"deep\" grouting layers are penetrated by cables to form a complete combination. The combination layers squeeze each other, which increases the friction resistance and reduces the rock deflection. The bending strength of the combination increases, and the overall bearing capacity of the surrounding rock mass of the roadway is improved. Figure 8: Layered grouting support structure. Figure 7: Grouting diagram. Figure 9 shows the mechanical model of the roof after layered grouting is established. The roof is simplified as a composite beam, and the grouting area is generally considered elastic. After grouting, the grouting layer will produce support resistance. The support resistance of the \"shallow\" grouting body is P1 and that of the \"deep\" is P2. L is the roadway width, a and b are the thicknesses of the \"shallow\" and \"deep\" grouting support layers, respectively, and h is the thickness of the composite beam of the grouting layer.