The effects of rock fragment content on the erosion processes of spoil heaps: a laboratory scouring experiment with two soils

摘要

Purpose Spoil heaps on newly engineered landforms create extensive artificially accelerated erosion, especially when there are catchment areas above spoil heaps, erosion caused by runoff will be much greater than that induced by rainfall. This study investigated the erosional characteristics of clay loam and sandy loam spoil heaps and proposed an appropriate hydraulic parameter to simulate the variation in erosion rate.Materials and methods A laboratory scouring experiment was conducted using a soil pan (dimensions 5mx1mx0.5m deep) with a discharging arrangement to test four samples of clay loam and sandy loam containing rock fragments (0%, 10%, 20%, and 30%) by mass. The slope of simulated spoil heaps was 53.2% with a discharging inflow rate of 15Lmin(-1). The rock fragments used were those commonly used in construction works, having a diameter of 2-3cm and irregular shape. Twenty-four scouring tests for eight treatments with duplication were accomplished in total.Results and discussion Average erosion rates showed a negative linear correlation with rock fragment content in clay spoil heaps (R-2=0.94) and a positive linear correlation in sandy loam spoil heaps (R-2=0.92). Rill width evolution of clay loam spoil heaps mainly developed at the early scouring stage (0-15min), and rills developed even more rapidly during later scouring times (30-60min) in sandy loam spoil heaps. Grey relational analysis showed that sheer stress and stream power both had higher Grey relational degrees with erosion rate for both soils, regression analysis showed that stream power can efficiently describe the erosional process of clay loam and sandy loam for each rock fragment content, but sheer stress only did well in sandy loam heaps.Conclusions Adding rock fragments to spoil heaps resulted in significantly opposite effects in the different soils; great attention should be paid to sandy loam spoil heaps due to their more severe erosion with increasing rock fragment content; stream power is an appropriate hydraulic parameter to simulate the soil erosion process of spoil heaps for both soil types.