# Experimental Study on the Bearing Capacity of Gas Oil-Contaminated Coastal Sand
## 4 Results and Discussion
### Physical Modeling Test Results
Moreover, the contamination of soils with hydrocarbons of high-lubrication potential (and possibly in low-apparent cohesion) might have more pronounced effects on the friction angle reduction and, consequently, make the friction term  
Figure 7: Variation in the bearing capacity of the foundation with respect to the subgrade density and contamination level. more influential in the bearing capacity of foundations. Therefore, the interplay between different terms of the bearing capacity equation may lead to different results. Figure 8a,b compare the calculated bearing capacity of the foundations using [PERSON]'s general bearing capacity equation with the measured values for loose and dense subgrades, respectively. The data derived from the direct shear test have been used in the calculations. Bearing capacity factors (i.e., \(N_{c}\), \(N_{q}\), and \(N_{\gamma}\)) were adopted from [PERSON] [53], and the shape factors \(\zeta_{c}\) and \(\zeta_{\gamma}\) were calculated using the equations presented by the [PERSON] [54]. Previous studies have shown that the bearing capacity factor, \(N_{\gamma}\), is dependent on the absolute width of the foundation for square and circular footings [45]. To account for the scale effects in the reduced-scale modeling, \(N_{\gamma}\) values were adopted based on the recommendations of [PERSON] and [PERSON] [45]. It can be seen in Figure 8a,b that the measured bearing capacity results are in acceptable agreement with those predicted based on [PERSON]'s bearing capacity equation for general and local shear failure. Except for the BC0-D and BC15-D, all measured bearing capacity values fall in between the predicted local and general failure values. [PERSON] [54; 55] has comprehensively studied the failure modes of footings rested atop sand at different relative densities and embedment depths. Using model testing, [PERSON] [54] identified three load-settlement curves, each ascribed to general, local, and punch shear failures. General shear failure was attributed to the curves with a peak and a postpeak reduction in the bearing capacity and soil bulging around the loaded footing. Local shear failure, on the other hand, exhibited limited bulging around the loaded footing with a load-settlement curve consisting of a higher initial slope, followed by a less-steep or almost-flat slope segment. Furthermore, the punching failure was attributed to curves with constant or a relatively modest decreasing slope in the loose sand, with the exhibition of almost no bulging around the loaded footing. [PERSON] [54] has shown that model foundations rested on sand demonstrate general shear failure at relative densities of 72% to 100%, local shear failure at relative densities ranging from 35 to 72%, and punching shear failure at relative densities of about 0 to 35%. In the present study, the failure mechanism of the model footings can be studied based on the load-settlement curves presented in Figure 6a,b, the bearing capacity results shown in Figure 8a,b, and the images from the subgrade condition at the end of loading (Figure 9). In this regard, according to the load-settlement curves presented in Figure 6a, it can be inferred that, other than the BC0-L curve, which almost shows a punching shear failure, other curves (i.e., BC5-L, BC10-L, and BC15-L) indicate shear failure mechanisms resembling the description of local shear failure. The results presented in Figure 8a also show that the measured bearing capacity results are quite near the predicted local shear failure values for the loose subgrade. Figure 8: Comparison of the predicted local and general bearing capacity with the experimentally measured results for (**a**) loose subgrade and (**b**) dense subgrade at different gas oil contents. Based on Figure 6b, for the dense sand, the general shear failure is the prevailing mechanism in all gas oil contents tested, except for BC15-D, which shows a load-settlement curve resembling that described for the local shear failure.