# Experimental Study on the Bearing Capacity of Gas Oil-Contaminated Coastal Sand
## 5 Conclusions  
The present study investigates the effects of gas oil contamination on the bearing capacity and shear strength of coastal sand in varying relative densities and gas oil contents. Direct shear testing and bearing capacity physical modeling have been utilized to study contaminated sand's behavior. As anticipated, increasing the relative density led to higher friction angles and, in turn, improved the foundation's bearing capacity for all gas oil contents studied.  
Physical modeling results demonstrated that the bearing capacity initially increases with the gas oil content up to a certain point, and then decreases. This pattern aligns with the findings of the direct shear tests, which show a substantial increase in the apparent cohesion up to a specific gas oil content. The direct shear tests also indicated that the lubrication of the sand particles due to gas oil contamination brought about an 8% reduction in the friction angle. Conversely, a significant increase in the apparent cohesion (attributed to soil suction) was observed, with an almost 5 kPa increase.  
Furthermore, the physical modeling test results in different gas oil contents align reasonably well with predictions based on [PERSON]'s general bearing capacity equation for both local and general shear failure. Improved precision can be achieved by correctly identifying the failure mode and using appropriate bearing capacity factors in the prediction equation. It is noteworthy that the measured bearing capacity of dense sand indicated general shear failure, while the loose subgrade leaned towards local shear failure. Additionally, it was observed that the dense sand exhibited maximum apparent cohesion and bearing capacity at a lower gas oil content compared to the loose sand.  
The results from both this study and prior research lead to the conclusion that the strength properties of hydrocarbon-contaminated soils are heavily dependent on the soil's properties and the type of hydrocarbon contamination. This study, in particular, highlights the notable influence of the relative density and saturation level on the mechanical behavior of hydrocarbon-contaminated sands. Therefore, it can be inferred that hydrocarbon  
Figure 9: Subgrade condition after loading (a) dry dense subgrade with apparent heave around the loaded area; (b) dense subgrade at a gas oil content of 5% exhibiting major bulging and heave around the loaded area; (c) dense subgrade at a gas oil content of 15% indicating minor bulging and heave around the loaded area.  
contamination may not always diminish the strength properties and bearing capacity of sands. Different parameters should be carefully assessed before taking highly conservative approaches in the design and retrofit of foundations rested on unsaturated hydrocarbon-contaminated soils.  
Conceptualization, A.K. and M.M.; methodology, A.K., M.M. and H.P.; investigation, A.K., M.M., H.P. and D.L.; resources, D.L.; writing--original draft preparation, A.K. and H.P.; writing--review and editing, A.K., M.M. and D.L.; visualization, A.K. and H.P.; supervision, D.L.; project administration, D.L.; funding acquisition, D.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (Ministry of Trade, Industry and Energy) (no. 20214000000180), and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) (2022400000220, Jeonbuk Regional Energy Cluster Training of human resources).  
Not applicable.  
Data presented is contained within the article.  
The authors declare no conflict of interest.