## 3 Results and Discussion
### Groundwater Effects  
Typically, pipes are buried above the groundwater table. However, the groundwater table may rise above a pipe as a result of a severe rainstorm or other unexpected events. To investigate the effects of groundwater, analyses were conducted on moist, saturated, and submerged soil conditions. For the submerged condition, the groundwater table was assumed to be located at the ground surface. The stress-pore pressure coupled modeling technique was adopted to investigate the coupled effects of stress and pore water on the performance of buried concrete pipes. In fully coupled modeling, both hydraulic boundary conditions and mechanical boundary conditions must be defined. Regarding hydraulic boundary conditions, a no-flow boundary was assigned at each of the four vertical boundaries of the buried concrete pipe. To prevent water from flowing into the buried pipe, the permeability of the buried pipe was set to zero. The pore-water pressures at both the right and left vertical boundaries were assumed to be constant throughout our analysis. To simulate rapid drawdown conditions, analyses were performed on fully saturated soils without a groundwater table. The saturated unit weight of the soil was then used in place of the dry unit weight. Since soil pressures are computed in terms of total stress, the pore-water pressure was subtracted from the computed soil pressures to obtain the effective stresses. The normal soil pressure distributions for moist, saturated, and submerged conditions under longitudinal loading are presented in Figure 6 for different backfill materials. The backfill materials are gravelly sand, silty sand, and silty clay in Figure 6a-c, respectively. All three backfill materials were deposited in native clay soil. Each figure contains four curves for the three conditions because there are two curves for the submerged condition: one for the effective stress and one for the total stress. Figure 6: _Cont._  
As shown in Figure 6, the average normal soil pressures are affected by the presence of the groundwater table. The effective soil pressure in the submerged condition is the lowest in terms of effective stress among the three conditions. However, below the lower haunch, the soil pressure in terms of total stress gradually surpasses the other three values because the pore water pressure increases with depth. The normal soil pressure distributions exhibit similar trends, regardless of the backfill material. A comparison of the normal soil pressures (effective and total) for moist, saturated, and submerged conditions at the crown, springline, and invert under the three different loading conditions (longitudinal, transverse, and uniform loading) is presented in Figure 7. Here, the trench is filled with silty clay. As shown in Figure 7a, the total normal pressure under the submerged condition is slightly lower than that under the saturated condition at the crown but is higher at both the springline and invert. Therefore, the presence of the groundwater table increases the normal soil pressure at both the springline and invert. In Figure 7b, it appears that under transverse loading, the soil pressures in terms of effective stress are the lowest for the submerged condition at all three analyzed locations. At the springline and invert, the soil pressures are the highest in terms of total stress for the submerged condition. For the uniform loading condition, Figure 7c reveals a similar trend; however, the pressure magnitude varies with the loading condition. Among the three loading conditions presented in Figure 7, the normal soil pressures are the highest under uniform loading at all locations, regardless of the presence of the groundwater table. The normal soil pressures under longitudinal loading are higher at both the crown and invert than those under transverse loading.