# Grouting Process Simulation Based on 3D Fracture Network Considering Fluid-Structure Interaction
## 2 Comparison Analysis
#### 3.2.2 Analysis of Structural Calculation  
In this section, the fractured rock mass in the study area is analyzed to explore the effects of fluid-structure interaction on the rock mass. The maximum and minimum principal stresses of rock mass are shown in Figure 11, which indicates that during the grouting process, most of the rock mass is subjected to compressive stress and the maximum compressive stress is 4.936 MPa. The area near the grouting borehole, the local boundary of the rock mass and fractures are partially subjected to tensile stress, and the maximum tensile stress is 3.361 MPa. The maximum tensile stress and the maximum compressive stress of the rock mass during grouting are less than the tensile strength (45.56 MPa) and the compressive strength (6.32 MPa) of the rock mass. Therefore, the rock mass of the grouting area will not generate new fractures or lifting deformation. In order to understand the influence of grout on the fracture aperture during grouting process, the aperture variation of fracture 1-1724 is analyzed at 50 s and 100 s. As shown in Figure 12, the maximum aperture increment happens at the intersection of grouting holes and fracture, and when at 50 s, the minimum aperture increment occurs at about 0.6 m where the grout front diffuses to. Then at 100 s, the grout diffusion length increases, the minimum aperture increment occurs at about 1.0 m, and the increment of the aperture along the grout diffusion distance is larger than that at 50 s. In summary, the aperture increment decreases non-linearly along the grout diffusion length and as the grouting time increases, the increment of aperture increases and the fracture deformation range expands. Figure 10: Variation of grouting diffusion length with time. Figure 13 shows the displacement vectorgraph of fractured rock mass, it can be seen that the aperture variation trend of primary fractures is approximately the same, for each fracture, the largest displacement occurs at the intersection of the fracture and grouting borehole, and the smallest at the end of the fracture. For secondary fractures, the displacement happens at the intersection of primary and secondary fractures. As shown in Figure 13, the maximum displacement of the whole area occurs at the lower fracture surface of fracture 1-1647, i.e., the region 2. This is because that the distance between fracture 1-1647 and fracture 1-872 is 0.43 m which is relatively close, fracture 2-220 intersects with fracture 1-1647 and inserts into the rock mass between fracture 1-1647 and 1-872, so the rock mass in this region is the most vulnerable and prone to deformation. Similarly, the region 1 is also the case where the fracture 2-220 intersects the fracture 1-1724, so that the rock mass in the region 1 becomes less rigid, but the fracture 1-1724 is farther from the surrounding fractures, so the deformation of the region 1 is smaller than the region 2. For fracture 1-872, we can see that the displacement of its upper surface is small. This is because the grouting process is conducted from top to bottom, so the fracture 1-1647 is grouted and deformation occurred before fracture 1-872, which offsets most deformation of the upper surface of the fracture 1-872. As for region 3, the distance between the fracture 3-2881 and the fracture 1-872 is small with 0.293 m, but the rock mass is still relatively rigid due to only a small portion of fracture 2-562 being inserted in the rock mass of this region, so that region 3 does not have large displacement. Overall, the maximum displacement of the entire area is 0.1181 mm, which is very small, so there will be no generation of new fractures and other adverse conditions in this area under the action of grouting. Figure 11: The principal stress contours. (**a**) The first principal stress contours, (**b**) the third principal stress contours. Figure 12: Fracture aperture variation along the grout diffusion length.