<p>This study investigates the influence of tensile strength at the foundation–soil interface on the performance of shallow foundations on clayey slopes. A self-developed Rigid Plastic Finite Element Method (RPFEM) is used to evaluate the undrained bearing capacity of shallow foundations subjected to eccentric vertical loading, with particular attention to the role of interface tensile strength. A comparative analysis of full-tensile and no-tensile strength models is conducted to evaluate their impact on the bearing capacity factor (<i>N</i>_c) and failure mechanisms. The study also examines the influence of slope geometry, including slope angle (<i>β</i> = 15° to 45°), slope height (<i>H</i> = 0.0<i>B</i> to 7.0<i>B</i>), and edge distance (<i>L</i> = 0.0<i>B</i> to 4.0<i>B</i>), where <i>B</i> is the footing width, on the normal stress distribution beneath the foundation base. In addition, the effect of eccentric loading direction is analyzed, and the results are validated against existing literature. The findings indicate that the no-tensile strength model more accurately captures the foundation–soil interaction under eccentric loading, with bearing capacity differences of 7–25% observed between the two models as eccentricity increases. Furthermore, the direction of eccentric loading significantly affects both stress distribution and bearing capacity, with up to 26% variation between positive and negative eccentricities. These results emphasize the importance of considering interface tensile strength and loading direction in predicting foundation behavior on slopes, thereby contributing to safer and more effective design under complex geotechnical conditions.</p>