Impact of rock fragment size on erosion process and micro-topography evolution of cone-shaped spoil heaps

Abstract

Spoil heaps in sites disturbed by construction cause severe acceleration of erosion, threatening environment quality and personal safety. Rock fragments (RFs) are a common component of spoil heaps; therefore, this study was conducted to evaluate the effects of different size classes of RFs on cone-shaped spoil heap erosion. A 3D laser scanner was used to capture the surface micro-topography evolution. A multi-day rainfall simulation experiment at 1.5 mm min−1 rainfall intensity was conducted with 30 mass percent of RFs of different diameters (1–3.5, 3.5–7, 7–10, 10–15 cm). The results showed that RFs reduced runoff by 13.0% relative to the bare soil spoil heap, among which the RFs of the 7–10 cm size class performed best. Only the initial surface micro-topography factors increased with RF size. The stable micro-topography factors of 1–3.5 cm RF treatment were 59.2% larger than those for other RF treatments on average because of the slope slump. Spoil heaps containing small size (1–3.5) RFs more easily slumped with an area of 0.895 m2 and showed obvious changes in micro-topography. RFs in different size classes influenced soil loss of spoil heaps via runoff yield and effects on slope stability. Larger roughness increment and runoff rate were associated with greater soil loss rate (R2 = 0.828), but time-varying roughness had no effect on runoff. Overall, the results of this study provide a better understanding of the impact of RFs on spoil heap erosion.