# Study on the Influence of Groundwater Variation on the Bearing Capacity of Sandy Shallow Foundation
## 2 Experimental Tests
### Analysis of Results  
The data-processing results of the tests are shown in Figures 4 and 5. In the figure, p represents the upper pressure, and s represents the displacement of the loading plate. Figure 4: The p–s curves at different water levels. Figure 3: The flowchart of the experiment. When the number of cycles is the same and the water level rises gradually from 0 to 50 mm, 100 mm and 150 mm, the foundation bearing capacity gradually drops from 360 kPa to 320 kPa, 260 kPa and 180 kPa, with a decrease of 11.1%, 18.8% and 30.8%, respectively. It indicates that the foundation bearing capacity decreased with the rise of the water level. With the gradual rise of the water level, the changes in the percentage of the foundation bearing capacity also increased. The increase in the water level improved the soil moisture content affected by water level, and the increase in the soil moisture content reduced the soil cohesion and internal friction angle. These are important factors that affect the bearing capacity of the foundation [32]. Specifically, the change of soil from an unsaturated state to a saturated state improved its plasticity. This makes it easier for the soil with a high degree of saturation to change from elastic to plastic under the same upper load, thus reducing the bearing capacity of the foundation. The rise in the water level is a process of increasing soil saturation, thus softening the soil and reducing the carrying capacity. When the water level was low, the bearing capacity of the foundation did not decrease significantly, because most of the soil in the soil was still in the unsaturated state and the shear strength was relatively high. However, when the water level increased, the soil-saturation degree increased. The bearing capacity of the foundation decreased obviously, and the softening of the foundation intensified. The bearing capacity of the foundation decreased from 260 kPa to 180 kPa, with a decrease of 30.8%, as the water level was the same, and the number of cycles increased from 1 to 15 times. The bearing capacity of the foundation decreased from 180 kPa to 170 kPa, with a decrease of 5.6%, as the number of cycles increased from 15 to 30 times. This indicates that the foundation bearing capacity decreased with the increase in the water-level cycle times, because the water-level cycle changed the soil moisture content successively. With the increase in the water-level cycle times, the soil moisture content increased, resulting in the decrease in soil cohesion and internal friction angle. With the increase in the number of cycles, the reduction of the bearing capacity became smaller. The reason is that, with the increase in the number of cycles, the proportion of saturated soil continued to increase. Eventually, the soil was fully saturated, and  
the simulation of real physical phenomena, it uses mathematical methods to solve the physical phenomena of the real world. It is good at solving the problem of multi-physical field coupling and can edit partial differential equations. As this problem is a fluid-structure coupling problem between water and soil, COMSOL can simulate this problem well. The Darcy seepage water storage model was adopted as the model, and the governing equation is as follows:  
\[\rho S\frac{\partial p}{\partial t}+\
abla\rho\bigg{[}-\frac{k}{\rho g}\bigg{(} -\frac{k}{\rho g}(\
abla p+\rho g\
abla D)\bigg{)}\bigg{]}=Q_{\text{m}} \tag{1}\]  
In the formula, \(p\) is fluid pressure, and \(\rho\) is the fluid density between the pores of the porous medium. In this study, \(\rho\) is the density of water. \(S\) and \(k\) represent the water storage coefficient and the permeability coefficient, respectively. \(Q_{\text{m}}\) represents the mass source term. When there is no external flow supply, \(Q_{\text{m}}\) = 0. \(\
abla D\) represents a unit vector in the direction of gravity. The Mohr-Coulomb law is a classical method that is used to study the strength of soil.