## 4 Analytical Results of the Gravel-Mixed Ground  
To clarify how the equivalent mechanical properties of the ground vary depending on the shape and content of gravel, a uniaxial compression-based numerical analysis model was used. The uniaxial compression test is a basic index for judging the mechanical properties of rocks when conducting a mechanical test of the ground material from which a tunnel is excavated, and it has a wide range of applications from soft rocks to unconsolidated rocks (Oshima, [16]). Therefore, the uniaxial compression numerical analysis model was used. For the numerical analysis, a plane strain model with dimensions discussed previously as shown in Figure 6 was created, boundary conditions were imposed at the bottom of the model, and then a self-weight analysis was performed. After this analysis converged, an evenly distributed load was applied on the upper part of the model. The equivalent elastic modulus of the model was calculated by dividing the vertical stress generated in the upper center element of the model by the strain calculated from the displacement (sinking amount) generated in the upper central node of the model. Using triaxial compression test results of a sample simulating conglomerate having a gravel content of 40% or less, [PERSON] [18] showed that the change in gravel content had little effect on the stress-strain relationship and was dependent on the physical properties of the substrate. When the gravel content reaches 60%, it is affected by the contact between gravel and is not controlled by the physical properties of the substrate. Thus, it is clarified that the gravel content of these intermediate regions (between 40 and 60%) corresponds to those transition regions. Therefore, Figure 7 shows the equival  
Figure 6: Uniaxial compression numerical analysis model. the difference between the two types of gravel modeling methods, the Voronoi division model, and the rectangular division model for investigating the magnitude of the effect of contact between gravel in a model with a gravel content of less than 40%. The relationship of gravel content is shown. Both the rectangular partition model and the Voronoi partition model shown in Table 1 were divided into three types. As is clear from Figure 7, the equivalent elastic moduli of both the rectangular division model and the Voronoi division model increase as the gravel content increases, but when focusing on the variation in the equivalent elastic modulus for all gravel content of each model, it is rectangular. It can be seen that the split model is larger, and the tendency becomes more remarkable as the gravel content increases. It is also found that the rectangular division model had a larger variation of the equivalent elastic modulus at a gravel content of 40% or more. In [PERSON]'s experiment ([PERSON] [18]) mentioned above, it was reported that this region exhibited a gravel content unaffected by the contact between gravel, but Figure 3a shows a method for expressing gravel, such as the rectangular division model. There is a possibility that the deformation of the ground is restricted because the gravel has sharp corners. Next, focusing only on the Voronoi partition model, in which the influence of contact between gravel is small under the ground condition where the gravel content is less than 40%, the relational expression between the gravel content and the equivalent elastic modulus is shown in Figure 8. It is seen that at a high content rate of 60-70% or more, the equivalent elastic modulus for each gravel content rate varied, and it was reported that the gravel content was affected by the contact between gravel in the study by [PERSON] [18]. A tendency similar to that of the region was observed. From this, it was found that the Voronoi partition model is a suitable method for expressing the ground properties of the ground mixed with gravel before tunnel excavation.