Objective This study aims to reveal how different reinforcement materials regulate infiltration, matric-suction dissipation, wetting-front advancement, and slope-surface erosion failure in fine-grained loess-fill slopes under intense rainfall, and to evaluate their anti-seepage and erosion-control performance.

Methods Typical loess fill from Jianshuigou, Chengguan District, Lanzhou City, was used to establish an indoor artificial intense-rainfall model-test platform. Four test conditions were designed: natural accumulation, geotextile, geogrid, and straw layer. The evolution of soil-water parameters and slope-surface failure processes was simulated under an intense rainfall condition of 125 mm/h. Volumetric water content, matric suction, wetting-front advancement, collapse depth, erosion rate, and crack development were monitored.

Results Different reinforcement materials exerted clear regulatory effects on water infiltration and erosion failure in loess-fill slopes. Under the geotextile condition, volumetric water content responded earliest and changed rapidly, while local runoff concentration and slope-surface collapse were relatively evident, indicating a comparatively weak anti-seepage effect. The geogrid delayed matric-suction dissipation at some monitoring points and postponed failure, but its peak erosion rate was relatively high, showing a delayed abrupt-change behavior. The straw layer effectively delayed infiltration response at the slope toe, slowed matric-suction dissipation, inhibited wetting-front advancement into deeper parts, and reduced slope-surface erosion and crack development. Under the straw-layer condition, the total erosion amount was 187.9 g, 15.9% lower than that under natural accumulation. At 120 min, the total crack length was reduced by 61.4% relative to natural accumulation.

Conclusions Different reinforcement materials affect erosion-failure modes of loess-fill slopes by changing infiltration paths, matric-suction dissipation, and slope-surface runoff distribution. Considering slope-toe infiltration response, wetting-front advancement, matric-suction dissipation, collapse depth, erosion rate, and crack development, the straw layer shows the best anti-seepage and erosion-control performance, followed by the geogrid, whereas the geotextile performs relatively weakly. The results provide an experimental basis for optimizing ecological reinforced protection and soil-water conservation measures for loess-fill slopes under intense rainfall.