# Experimental Study on the Bearing Capacity of Gas Oil-Contaminated Coastal Sand
## 4 Results and Discussion
### Direct Shear Test Results
[PERSON] and [PERSON] [31] explained that the bonding created between particles due to hydrocarbon contamination can generate cohesion due to their adhesion capacities. This effect is more pronounced at lower contamination levels, where the amount of hydrocarbon does not significantly influence the frictional behavior of the sand particles. Thereafter, augmenting the hydrocarbon concentration thickens the contact layers and fills empty  
Figure 5: (**a**) Shear stress vs. normal stress; (**b**) Variation in friction angle and apparent cohesion for dense samples at different gas oil contents. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Gas Oil Content (\%)**} & \multicolumn{2}{c}{**Dr = 30\%**} & \multicolumn{2}{c}{**Dr = 70\%**} \\ \cline{2-5}  & \(\gamma_{d}\) = 14.19 (kN/m\({}^{3}\))** & **e = 0.866** & \(\gamma_{d}\) = 15.14 (kN/m\({}^{3}\))** & **e = 0.749** \\ \cline{2-5}  & **C (kPa)** & \(\varphi\) (\({}^{\circ}\)) & **C (kPa)** & \(\varphi\) (\({}^{\circ}\)) \\ \hline
0 & 0.12 & 33.2 & 0.1 & 35.1 \\
5 & 2.3 & 32.6 & 5 & 33.4 \\
10 & 3.05 & 31 & 4.4 & 33 \\
15 & 1.2 & 31 & 1.5 & 32.4 \\ \hline \end{tabular}
\end{table} 
Table 5: Apparent cohesion and friction angle in different relative densities and gas oil contents. sand pores, which weakens the frictional behavior and reduces the induced cohesion. In a related study, [PERSON] et al. [49] proposed that hydrocarbon-induced cohesion within soil pores compensates for reduced particle roughness. This, in turn, leads to a stable trend in the soil shear strength, as the reduction in the friction angle combines with hydrocarbon-induced cohesion. Although the viscosity-induced apparent cohesion might contribute to the increase in cohesion, a significant portion of the cohesion generated may be due to the suction generation as a result of the hydrocarbon contamination. The mechanism of apparent cohesion increase is quite similar to the suction-induced apparent cohesion in unsaturated soils, which is the highest at lower degrees of saturation and reduces as the saturation level increases. [PERSON] et al. [50] investigated the unsaturated shear strength of diesel-contaminated clayey soils. They reported a significant increase in the shear strength of diesel-contaminated soils compared to uncontaminated specimens, especially in large normal stresses. Their findings showed that this increase is due to an almost 150% increase in the total suction of the contaminated specimens compared to the uncontaminated specimens. It can be seen that, compared to the loose samples, the dense samples reached their highest cohesion in a smaller gas oil content. This is primarily due to the fact that the suction-induced cohesion is greatly dependent on the void ratio of the soil samples [26; 51]. [PERSON] et al. [52] have also shown that the oil retention and transport properties are greatly dependent on the density and water content of the polluted soil. As dense samples have a smaller void ratio, the saturation degree increases with a smaller amount of gas oil, the sand mass reaches its suction peak at smaller gas oil contents, and the suction drop starts at smaller gas oil contents.