## 6 Conclusions  
In this study, the variability and uncertainty in horizontal earth pressure on a box culvert were evaluated through a centrifuge model test. Horizontal earth pressure was measured using three measuring sensors attached to the side of a box culvert, and the parameters were gravitational acceleration and cover depths under loading and unloading conditions. The contents and results of the experiment and statistical analysis were shown in the main text, and the conclusions are as follows. 1. As a result of all centrifuge model tests, the horizontal earth pressure had a larger value in the unloading condition than in the loading condition. This is considered to be the residual stress that occurs when the gravitational acceleration was applied by this process (10 g \(\to\) 20 g \(\to\) 30 g \(\to\) 40 g \(\to\) 50 g \(\to\) 40 g \(\to\) 30 g \(\to\) 20 g \(\to\) 10 g). In addition, the loading condition is a general state in the ground, and the vertical stress (friction force) acting on the side wall of box culvert acts in the upward direction. However, in the unloading condition, the vertical stress acts downward because of the rebound of the sand and over-consolidation state. Because this rebound is larger with more soil, the higher the cover depth and the deeper the sensor position, the greater the difference in horizontal earth pressure is due to the same occurrence of loading and unloading. It is judged that the difference in horizontal earth pressure according to loading and unloading occurs significantly with higher cover depth and lower sensor position. 2. For \(\sigma_{\text{h}}\), the centrifuge model test result had a larger value than the existing theoretical value. This is the result of overestimation of \(\sigma_{\text{h}}\) during the test process. The causes of overestimation of measurement results can be analyzed in two ways; (1) Sensor location: The sensor should be installed inside as much as possible, but it protrudes partially during the installation process or the gravitational acceleration application process; (2) Interface: Measurement of a large value because the friction coefficient of the soil in contact with the surface of the sensor is larger than expected. 3. As the gravitational acceleration was increased, \(K_{0}\) tended to decrease and converge to a specific point, and the variability significantly decreased. It is judged that this is a result of a decrease in ground variability rather than a decrease in the average value. As the variability decreased, data points with differences from the mean disappeared, which increased the reliability of the experimental results. In the influence of the cover depth, it was confirmed that each sensor position (Top, Middle, and Bottom) of 50 g had a similar value regardless of the cover depth. Based on this, it was confirmed that when the centrifuge model test was performed, the variability of the result was reduced, and an accurate value was obtained if the gravitational acceleration was set to a certain point or higher. Therefore, it is necessary to analyze the correlation between the model production size and the gravitational acceleration. 4. In this study, the variability analysis of the horizontal earth pressure acting on the box culvert was performed. It is important in that it proposes the causes of volatility and methods to reduce variability. However, there were limitations in that the difference between the measured value and the predicted value was large, and the size effect and repeated loading was not confirmed. 5. There was a big difference in the horizontal earth pressure when compared with the reference values. This means that there is a possibility that the used internal friction angle was changed in the centrifuge model test due to rebound according to loading and unloading, which could be the size effect of the ground composed of sand.