Unsaturated loess slopes in the Three-River Source Region of Qinghai are prone to landslide hazards under rainfall infiltration. To investigate the influence of rainfall on slope stability in this region and the effectiveness of ecological slope protection, this study first determined the basic physical properties, shear strength under controlled matric suction (50–200 kPa), and soil-water characteristic curves of undisturbed samples through laboratory tests. A transient seepage–stress coupled f