Study On The Characteristics Of Soil Erosion And Micro-topography Evolution Of Spoil Heaps As Well As The Interacting Mechanism Between Them

Soil erosion in site of production and construction projects is the main source of man-made accelerated soil erosion in our country,and spoil heaps are one of the most severely eroded land-forms on these disturbed surfaces.However,previous studies not only simplified the characteristics of rock fragments contained in spoil heaps and thus failed to reflect the effect mechanism of rock fragments in the process of soil erosion,but also ignored the impact of micro-topography and soil clods on erosion.Therefore,this study used artificial rainfall simulation,field observation and three-dimensional laser scanning techniques to study the water erosion process and micro-topography evolution of the heavy soil spoil heap under the treatment about rock fragment,rainfall intensity,soil clods.Further to explore the interactive relationship between micro-topography evolution and soil erosion.Finally,integrate the research results in this study to provide some suggestions and ideas for the revision of the soil loss calculating model of spoil heap.The main conclusions are as follows:(1)The increase in rock fragment content leads to prolonged initial runoff time and reduced runoff rate on the slope.The erosion rate first increases and then decreases with the increase of rock fragment content.A smaller content of rock fragment(0?30%)can promote soil erosion on the slope,especially the content 30%caused a maximum erosion amount;when the rock fragment content>30%,the erosion rate is significantly reduced,when the gravel content increases to 75%,the amount of soil erosion is almost zero.Under different rock fragment size treatments:the runoff rate first decreases and then increases with the increasing rock fragment size.When the size is 7—10 cm,the runoff rate is the smallest,which is related to the adjustment mechanism of the rock fragment to the internal pores of the soil.In general,when the spoil heap contains 30%rock fragments with smaller-size(1—7cm and mixed),landslides are prone to occur and the soil loss amount is greater.Among the two factors of rock fragment content and size,content dominantly impact of runoff and soil erosion characteristics,with a contribution rate of>50%.(2)When the total rainfall is constant,the soil erosion of the spoil heap under the long-lasting light rain is more severe.Under 1.0?2.0 mm/min rainfall intensity,the presence of soil clods can reduce runoff by 12.1?29.4%,but increased the soil loss amount by 20?230%.Field observation results show that the runoff yield gradually decreases with the increase of rock fragment content,and the amount of soil erosion first increased and then decreased with the increasing rock fragment content,and reached the maximum at 10%content.The change trend was the same as the results of laboratory experiments.The soil loss amount is significantly related to the cumulative natural rainfall,with a correlation coefficient of 0.969?0.986,while the rainfall intensity had no significant effect.(3)The surface roughness first increased and then stabilized with the accumulated rainfall,and the main changes occurred in the first two rainfalls.Among them,the roughness of up-slope position>middle-slope position>down-slope position,indicating that the up-slope position has the most serious terrain fragmentation due to rainfall erosion.The initial roughness increased with both increasing rock fragment content and size.After rainfall,due to the larger-scale landslide under the treatment of 30%rock fragment content and 1—3.5 cm size,the micro-topography factor is significantly larger than other treatments,while the difference between other treatments is not significant.In the continuous rainfall process,the drainage network gradually converges with the erosion development,which leads to the increase of the sinuosity of the flow path and the decrease of the flow path gradient.On the whole,there is no significant difference in the characteristics of the drainage network under different rainfall intensities.(4)The increase in surface roughness is beneficial to prolong the initial runoff generation time of the spoil heaps,but has no significant effect on the average runoff rate of a single rainfall event;the surface roughness has a significant positive correlation with the average soil erosion rate,the erosion extent of the spoil heap with larger roughness is more severe.For the drainage network,the drainage density and runoff frequency both have a significant negative correlation with the surface roughness.Stream power is the most sensitive hydrodynamic parameter to the changes in the drainage network characteristics,with the correlation coefficient between 0.644 and 0.832,which has a good linear relationship with the drainage density,path sinuosity and gradient(R~2=0.961?0.979).(5)Field observations show that the average relative error of the spoil heap erosion model is 26.7%which is satisfactory.When the rock fragment size is increased(3.5—14 cm)or mixed,the factor G calculated by model formula is on the high side.And the larger the rock fragment size,the smaller the rock fragment content,the greater the deviation.In addition,the clods those the spoil heap contains in actual conditions will cause the erosion amount to be larger than the predicted soil loss amount by the model.The micro-topography is an important indicator for measuring the amount of erosion when gravity erosion occurs,which cannot be ignored in future revision of the model.