Effect Of Medicago Sativa Planting Density On Slope Erosion Of Engineering Accumulation

With the rapid development of society and economy,various production and construction projects across the country have produced a large number of disturbed ground and spoiled soil and slag engineering deposits during the implementation process,causing serious land resource destruction,landscape damage and man-made soil erosion.The soil erosion of engineering deposits is higher than that of agricultural land.Besides,the soil erosion is also uniqueness and differences,which has become one of the main sources of new soil erosion.Under normal circumstances,it is difficult to transport and dispose of engineering deposits in a short time period.It is urgent to take rapid protective measures.Grass covers on its slope is one of the effective measures to prevent soil erosion.However,the current situation for vegetation control engineering deposits the mechanism of loss is still unclear,especially the influence of grass planting density and the aboveground and underground parts of vegetation on the slope erosion of the engineering deposits of the regulation and control is relatively weak.Therefore,this paper took the newly piled engineering deposits as the research object,adopted the artificial hole sowing method,planted Medicago Sativa with different densities on the surface of the accumulation,and used the field simulation rainfall test to analyze the different density of Medicago Sativa and its effect on the aboveground and underground parts.Analyzed the influence of different Medicago Sativa densities and their aboveground and underground parts on the law of runoff and soil erosion,hydrodynamic characteristics and benefits of runoff and sediment reduction on the slope of the engineering deposits.The main conclusions are as follows:（1）The increase of vegetation planting density promoted the transition from rapid to slow on the slope of the engineering deposits,and the vegetation coverage increased the critical runoff shear stress and runoff power of the engineering deposits.Under various rain intensity conditions,when the planting density is PD₁₀（10 cm×10 cm）,the runoff flow pattern of the engineering deposits was subcritical-laminar flow,and PD₁₅ and PD₂₀ were subcritical-laminar flow and supercritical-laminar flow.Because vegetation growth disturbed the engineering deposits,the increase of planting density weakened the critical runoff shear stress and runoff power of the engineering deposits,and the weakening effect was strongest as the rainfall intensity is 0.8 mm/min.The soil erosion rate of the engineering deposits has a significant linear function relationship with runoff shear stress and runoff power（P<0.05）.Under the same rainfall intensity conditions,the critical runoff power and critical runoff shear stress of the vegetation covered engineering deposits decreased with the increase of planting density.The critical runoff power and critical runoff shear stress of the planting density of PD₂₀ were 1.50～3.00 times and 1.10～2.50 times than that of other planting densities Runoff power was better than runoff shear stress in describing the erosion dynamics of vegetation cover engineering deposits.（2）Vegetation protection could effectively slow down the runoff on the slope of the engineering deposits,reduced the runoff and sediment production,and controlled the water and sediment steadily.Compared with the bare slope,the runoff generation time of the vegetation covered engineering deposits was extended by 0.71～3.94 min.With the increase of planting density,the vegetation slowed down the runoff increased by 12.79%～264.75%,and the runoff rate and soil erosion rate decreased by 0.92%～69.68%and 0.66%～95.78%.Compared with the bare slope,the vegetation coverage slope is 60.20%～90.09%and53.33%～98.54%lower than that of the bare slope.The relationship between water and sediment on the bare slope fluctuated,and the soil erosion rate of the engineering deposits covered by vegetation has a significant linear function relationship with the runoff rate（P<0.05）.（3）The underground part could reduce the sediment production on the engineering deposits in the early stage of runoff,but accelerated the erosion in the later stage of the runoff,and the sediment increase rate reach to 285.24%.When the rainfall intensity was 0.8 mm/min,the contribution of underground flow reduction and sediment reduction was higher than that of the aboveground part.The former increased 13.71%～127.32%and 58.74%～490.44%compared with the latter and showed a fluctuating growth trend when the rainfall intensity was1.2 and 1.8 mm/min.In the later stage of runoff generation,the underground part will accelerated the sediment production on the slope.The low reduction and sediment reduction contribution of the aboveground part were higher than the underground part.The flow reduction contribution of aboveground part increased by 3.66%～739.59%and 8.19%～189.64%than underground part.