## 3 Geotechnical Centrifuge Model Test
### Ground Composition  
Sand was used in the centrifuge model test, and the particle size distribution curve from the sieve test according to ASTM D2487 [24] is shown in Figure 5a. The coefficient of uniformity (\(C_{u}\)) and coefficient of curvature (\(C_{c}\)) of the soil, as calculated from the particle size distribution curve, are 4.09 and 1.18, respectively. Accordingly, the soil was classified as poorly graded sand according to the USCS (Unified Soil Classification System). In addition, the ASTM D698 standard compaction test [25] was performed to determine the degree of compaction for the ground composition process. The result is shown in Figure 5b: the maximum dry unit weight is 1.715 t/m\({}^{3}\), and the optimum water content is 8%.  
The degree of compaction was set to 95% for dense ground, and the dry unit weight of the model ground was 1.66 t/m\({}^{3}\), according to the maximum dry unit weight presented in Figure 5b.  
The simplest method for ground composition is compaction using the impact from a hammer. Moreover, when precise conditions, such as those in the centrifuge model test, are required, this problem becomes more serious. Therefore, in this study, the ground was composed via the sand pluviation method using the funnel, as shown in Figure 6. The sand pluviation method using the funnel involves compacting the sand through a steel pipe of a certain diameter. This method reduces the amount of time and area in the air over which the sand falls. Therefore, material separation (difference in falling speed with particle size) can be minimized, as well as sensor damage or malfunction.  
Figure 5: Results of laboratory test: (**a**) Particle size distribution obtained from sieve test and (**b**) compaction test to determine maximum dry unit weight and optimal water content.  
Figure 6: Sand pluviation using funnel: (**a**) Schematic diagram, (**b**) Ground composition and (**c**) Procedure of pulviation.  
Sand pluviation is performed in the vertical direction up and down (red line), and then in the transverse direction (blue line). This process is then continuously repeated to form the ground. Finally, numerous experiments were conducted for target degree of compaction (95%). The length of the steel pipe was 2.0 m, and the diameter of the sieve was 4 mm, as is required for 95% degree of compaction.  
Particle size effects can be seen when testing different sized models on the same soil. The smaller the ratio of the model to the mean particle size, the higher the value of the axial friction and point resistance. Therefore, it is necessary to prove the homogeneity of the ground through a small cone penetration test [26; 27; 28]. For the sand pluviation method, the work skill of an experienced experimenter is the most important, and the homogeneity of the composed ground must be secured. However, in this study, the cone penetration resistance according to the gravitational acceleration could not be confirmed, and the cone penetration resistance according to the initial ground composition was confirmed, as shown in Figure 7. Based on the linear increase trend, homogeneity was confirmed in the initial ground composition process.