## 3 Results and Discussion
### Loading Effects  
A buried pipe may be subjected to different loading conditions depending on how loading is imposed on the pipe. Longitudinal, transverse, and uniform loads can be imposed on buried pipes. Under the longitudinal loading condition, surface loading only covers the trench width in the longitudinal direction. Under the transverse loading condition, surface loading covers one-third of the entire model surface in the transverse direction. Under the uniform loading condition, the load covers the entire model surface. The normal soil pressure distribution around a buried concrete pipe was analyzed under longitudinal, transverse, and uniform loading conditions. The analyzed normal soil pressures were then plotted along the central angle measured clockwise from the crown of the buried concrete  
Figure 3: Crack analysis method: (**a**) crack detection and (**b**) crack depth. pipe. The surface loading was kept constant at 500 kPa for all conditions to allow for the direct comparison of results. The normal soil pressure distributions under different loading conditions for gravelly sand, silty sand, and silty clay backfills, as well as clay and sand native soils, are presented in Figure 4. The cross-sectional view of the transverse loading condition was captured at the central axis of transverse loading. For all conditions, a distinct feature of the corresponding distribution is that the pressure decreases from the crown to the springline, increases from the springline to the lower haunch, and then decreases to the invert. The soil pressure distribution for the uniform surface loading condition should be the same as that without any surface loading (geostatic condition), except that the magnitudes of the values under the geostatic condition should be smaller. As illustrated in Figure 4a, the average normal soil pressures are heavily influenced by the loading type. The lowest and highest average normal soil pressures occur for the transverse and uniform loads, respectively. One plausible explanation for this phenomenon is that higher normal soil pressures are induced by higher confining pressures under uniform loading conditions. Additionally, the normal soil pressure under transverse loading conditions at the springline is greater than that under longitudinal loading conditions. This can be attributed to the fact that the confining pressure under the central axis under transverse loading conditions is greater than that under longitudinal loading conditions. Figure 4: Variations in the normal soil pressure distributions under longitudinal, transverse, and uniform loading: (**a**) SW95 in clay native soil, (**b**) ML95 in clay native soil, (**c**) CL95 in clay native soil, and (**d**) SW95 in sand native soil. Furthermore, unlike the pressures obtained under uniform and transverse loading conditions, the normal soil pressures at the springline under longitudinal loading conditions are nearly zero. These very low normal soil pressures at the springline could be partially attributed to the shear resistance mobilized along the vertical interface between the trench wall and native clay soil. This shear resistance reduces the surface loading effects on the normal soil pressure. As illustrated in Figure 4b,c, the patterns of the normal soil pressure distributions for silty sand and silty clay are similar to those for gravelly sand. The induced soil pressures for gravelly sand under both longitudinal and transverse loads are almost equivalent at the invert. However, the induced soil pressures under transverse loading for silty sand and silty clay are greater than those under longitudinal loading at the invert. Figure 4d presents the normal soil pressure distributions under different loading conditions for the gravelly sand backfill material in the sand native soil. The trends in the normal soil pressure distributions are similar to those for the clay native soil presented in Figure 3a. The normal soil pressure at the springline under longitudinal loading is greater than that in clay native soil.