<p>Stabilizing slopes with weak thin layers aligned obliquely to the slope surface requires tailored geogrid reinforcement to mitigate shear failure risks. This study employs 3D finite element analysis to optimize geogrid configurations (3–6 layers, 300–1200 kN/m tensile strength) for such slopes. Results show that an increasing number of layers and tensile strength improve stability, with diminishing returns beyond 5 layers and 800 kN/m. The optimal configuration–5 layers at 800 kN/m–yielded a factor of safety of 2.2, reduced displacement by 96%, and lowered maximum shear strain below 0.02%, compared to unreinforced slopes. Reinforcement also reduced shear stress concentrations by 67% and disrupted the continuous slip surface, redistributing plasticity. Mobilized axial forces in geogrids remained below pullout capacities across all cases, confirming secure anchorage without pullout risk. These findings highlight strategic geogrid placement and moderate tensile strength balance efficacy and cost, offering a practical framework for the stability of slopes with oblique weak layers.</p>