# Theoretical Approach to Predicting the Diffusion Radius of Fracture Grouting in Soil-Rock Mixtures
## 4 Results and Discussion
### Mechanism of Slurry Diffusion of Indoor Grouting Tests
Figure 13: Concretion fragment of Groups #1–3. In group #1-3 tests, the slurry diffusion form was mainly in the form of fracture, and the diffusion radius of fracture grouting was between 20 and 40 cm. Although there was a small range of permeation grouting, the permeation grouting mainly occurred on both sides of the fracture surface, and the permeation grouting was attached to the fracture grouting with a permeation width of approximately 3-6 cm, which had little influence on the overall diffusion radius. Therefore, we considered the form of slurry diffusion in groups #1-3 as fracture diffusion. The test concretions in groups #7-9 were irregularly spheroidal, as shown in Figure 12g-i, where the slurry was evenly distributed with the soil and stones and glued to each other to form a whole, showing prominent permeation grouting characteristics, and their permeation grouting radius was between 25 and 40 cm. However, through careful observation, there were still features of fracture grouting on the concretions, as shown in Figure 15, which shows a partial view of the surface of the concretion of group #7. There were fracture grouting veins raised on the surface of the concretion, with clear lines, and there was no soil and stone inside, which is caused by fracture grouting. The fracture plane was formed by the extension of the surface of the concretion formed by permeation diffusion. As a rule, when the permeability coefficient of the soil body is large, and the slurry has good groutability, it is not easy to produce fracture. This shows that when the radius of permeation grouting diffusion is large enough, the slurry fills the pores of the soil-rock mixtures, which makes the groutability poor, and the slurry will compress the soil body deformation under the action of grouting pressure and even make the soil body yield to crack. Then, the slurry is pressed into the cracks to cause fracture grouting. Figure 14: Concretion section of Group #3. According to the morphology of the concretions, groups #4-6 had a permeation grouting concretion centered on the grouting pipe opening, which was irregular and spherical in shape, with a radius of 10-25 cm. Additionally, there were several fracture faces in the concretions, and the permeation grouting concretions were weakly connected to the extended fracture faces, which were broken by the concentrated stress during dumping. The smaller fracture face fragments were challenging to recover, so the largest fracture face was taken as a representative, and its fracture grouting radius was measured, with a value of 10-20 cm. The difference between the radius of permeation grouting and the radius of fracture grouting was insignificant, so for groups #4-6, the slurry diffusion was in the form of both permeation and fracture diffusion. Therefore, the concretion consisted of two parts: one is the permeation grouting concretion centered at the mouth of the grouting pipe, and the other is a maximum fracture plane, as shown in Figure 12d-f.  
For soil-rock mixtures with 50% stone content, permeation grouting, fracture grouting, or even both may occur under uniform soil-rock mixtures. This situation shows that the slurry is generally groutable for soil and rock mixtures with 50% stone content, and the slurry's permeability depends on the slurry's viscosity, the void ratio of the soil-rock mixtures, and the grouting pressure value. At the same time, the fracture pressure of the soil was less than the minimum grouting pressure in the test, which was 0.4 Mpa. Therefore, for soil-rock mixtures with stone contents near 50%, the design of grouting technical parameters should be carried out more strictly to ensure that the grouting effect is within the expected range.