Soil erosion process of engineering accumulation in steep slope under simulated runoff conditions

Abstract: Deposits during the process of engineering construction have unique soil constitution and complex conditions of underlying surface, characterized by weaken anti-scourabilty attributed to loose textures, lacks of soil structures, insufficient plant roots, soil organic matter deficiency and so on. Erosion response of steep deposit slope to hydrodynamic conditions show different characteristics, a set of field pouring water scouring experiments were conducted on steep slope with 72.7% gradient and 12-meter length of typical spoil ground along the line of freeway to investigate the soil erosion process of deposit slope under simulated runoff conditions. Watering system consists of a diving pump, a water knockout vessel, a still well, valves, switches and pressure pipes. During the process of each experiment, the slope was divided into 4 sections by 3-meter-intervals down slope, where flow velocities，flow widths and flow depths were measured by the method of dye tracing and the use of thin steel rule during sampling. The runoff and sediment sample was taken at 1-minute-intervals within 3 minutes after runoff initiates, where after, the sample was taken at 3-minute-intervals, and in the whole experiment all the runoff and sediment were collected. The results show that runoff intensity is closely related to discharge intensity and sediment concentration, presenting multivariate linear correlation by grey correlation degree analysis and correlation analysis of various factors influencing runoff intensity, which can be expressed as follows: M=0.818 P-0.758S-0.276 (R2=0.90), indicating that discharge intensity has a positive effect on runoff intensity, on the contrary, the sediment concentration has a negative effect on runoff intensity. Gravitational erosion caused by ascending sediment concentration during erosion process has large influence on the variation of sediment concentration, which has a critical discharge of inflow under test conditions with 20L/min and 25L/min. The process of slope sediment yield falls into three stages: abrupt, fluctuation and stable, and spatial distribution of sediment yield along different slope profiles under different runoff conditions can be reduced to two types: steady decrease and violently fluctuating reduction. Soil detachment rate is linearly related with unit discharge(Dr=0.693q+3.97, R2=0.781), which can also be expressed as the power function of sediment yield and flow width in different time-intervals(Dr=1.689U0.671b-0.669, R2=0.799). Moreover, sediment yield in any time-interval can be described with power function of run-off in the same time-interval(M=0.5548V1.036, R2=0.822) and accumulative sediment yield increases linearly with the increase of cumulative run-off(Us=0.687Q+6.123, R2=0.975). The results indicated that Soil erosion characteristics of steep deposit slope formed by engineering construction activities are distinct from that of conventional agricultural soils, indicating that soil erosion researches on production and construction areas should be carried out on the basis of clarifications of disturbance and intensity. The conclusions reveal that regulation of slope runoff is still an important approach to achieve comprehensive control of soil erosion on engineering and construction areas.