| According to the study, main conclusions showed as follow:(1) The results showed that the types of spoilbanks had no significant effect on runoff rate, while the gravel content could delay the time that runoff rate reaches stable. The erosion rate appeared in multimodal distribution with the rainfalls time. Both gravel and the type of rolling compaction by construction machinery at the top of slope increased the total sediment yield a lot. The total sediment yield of the type of scattered cone, which contains some gravel(10%), was 1.92 times higher than that of the type of scattered cone, which contains no gravel, when the rainfall intensity was 90mm/h. Meanwhile the type of rolling compaction by construction machinery at the top of slope produced 1.5 times of the total sediment yield than the type of scattered cone, when both of them contain no gravel. The average runoff rate and average erosion sediment rate of all types accorded with linear correlation with rainfall intensity significantly. The total sediment yield and runoff volume showed an apparent linear relationship as well.(2) In this study, the laterite of Northern Jiangxi was selected as research objects. Through conducting rain simulation experiments which used deionized water under different mass percentage of gravel(0%, 10%, 20%, 30%), and different rainfall intensities(1.0, 1.5, 2.0, 2.5mm/min), the effects of rock fragment on soil erosion rule of engineering pyramidal accumulation in Northern Jiangxi was discussed. The results were given in the following, under the same rainfall intensity, the contributing time of the pyramidal accumulation could be reduced if gravels present. While the relationship between the runoff rate and the mass percentage of gravel was inconspicuous, the runoff rate increased as the rainfall intensity did. When the rainfall intensity ≥1.5mm/min, these four types of engineering pyramidal accumulation mainly experienced four stages: the erosion of surface soil, the formation of soil crust, the reduction of erodible soil, and the destruction of soil crust, in a rain that lasted 60 min. The presentation of gravels could increase the total sediment yield, in other words, the larger the mass percentage of gravel was, the more sediment was yielded.(3) Soil erosion newly derived from engineering spoilbank severely threatens ecological safety of construction sites and surrounding areas. Engineering spoilbank with three – dimensional is quite different from the traditional slope, as a result, to study the hydrodynamic process of a three – dimensional engineering spoilbank is of great necessity. In this study, in order to find the best hydrodynamic parameters that can describe the hydrodynamic process of soil erosion caused by tapered engineering spoilbank, laterite collected from the north area of jiangxi province was selected as the main test material and variations in hydraulic parameters(flow shear stress, stream power, unit stream power, unit energy of water-carrying section) of overland flow were studied experimentally. This study was processed in inner-door rainfall experimental condition. Three kinds of artificial intensities(1.0 mm/min, 1.5 mm/min, 2.0 mm/min) and three gravel content(10%, 20%, 30%) were designed. Every experiment persisted 33 min during when there was no erosion gully occurring on the surface of the tapered engineering spoilbank. The result shows that: 1) When it comes to one independent hydrodynamic parameter, both its instantaneous value and average value were closely related to soil detachment rate except the cross-section specific energy. To be more specific, both the flow shear stress and the instantaneous flow shear stress had a significant power function relation with the corresponding detachment rate and this relationship also occurred between the stream power and the detachment rate, while, the relationship between unit stream power(or the instantaneous unit stream power) and the detachment rate(or the instantaneous detachment rate) was linear. In terms of the cross-section specific energy, its instantaneous value had no obvious relations with the instantaneous detachment rate though its average value had a power function with the average detachment rate; 2) Critical unit stream power for surface erosion of the tapered spoilbank was 6.8×10-3 m/s, and the critical instantaneous value of surface erosion parameter tended to be less which was 3.8×10-3 m/s. Moreover, the erodibility parameter of experimental material was about 0.0053 ~ 0.0059 s2/m2, that was 20 ~ 30 times larger than the pure clay. So, the conclusion was that soil which mixed with gravel on the spoillbank surface was more easily carried away by the overland flow than the pure clay which was not stirred. 3) Giving the relevance between the instantaneous cross-section specific energy and the instantaneous detachment rate was extremely low(R2=0.130), instantaneous cross-section specific energy was not suitable to be a hydrodynamic parameter describing the hydrodynamic process of soil erosion caused by tapered engineering spoilbank. 4) With regard to fitting effect, the parameters tested should be ranked in the order of stream power>instantaneous stream power>unit stream power>flow shear stress>instantaneous unit stream power>instantaneous flow shear stress > cross-section specific energy,obviously stream power had the best correlation(power function) with the soil detachment rate(R2=0.972). So stream power was the best one of all the hydrodynamic parameters tested to describe the hydrodynamic process of soil erosion caused by tapered engineering spoilbank. What is more, owing to stream power is a kind of energy rather than stress, it tends to be more scientific to study the erosion process of tapered engineering spoilbank on the energy hand. In summary, the hydrodynamic process of a tapered engineering spoilbank is quite different from a slope’s. The result obtained may lay the foundation for the establishment of process-based model of soil erosion initiated by engineering spoilbank, and provide scientific guidance for comprehensive control of newly arising soil and water loss in production and construction areas.(4) In this study, the laterite of Northern Jiangxi was selected as research objects. Through conducting rain simulation experiments which used deionized water under different mass percentage of gravel(0%, 10%, 20%, 30%), and different rainfall intensities(1.0, 1.5, 2.0, 2.5mm/min), the flow velocity, the runoff sediment concentration as well as the erosion rate of engineering pyramidal accumulation in Northern Jiangxi was discussed. The results show that the flow velocity stayed relatively stable alone the rainfall time, and it is a result which the rainfall intensity and the mass percentage of gravel cause. A formula about the relationship among flow velocity, rainfall intensity and mass percentage of gravel was given. While the relationship between the runoff sediment concentration and the rainfall time was comparatively complex, the runoff sediment concentration increased first, than decreased in low amplitude and stayed stable later, after a duration of stability, it decreased dramatically again, but at the last of the rainfall, it appeared a decrease. According to the results, we found that the spoilbank got new erosion at the time of 48 min.Erosion rate increased with both the rainfall intensity and the mass percentage of gravel increased, and a formula was given.(5) In this study, a type of Spoilbank(rolling compaction by construction machinery at the top of slope) was selected to study the law of soil erosion process that affected by two kind of gravel in indoor rainfall experimental condition. The results showed that the difference of gravels had a little influence on the erosion mechanism. While it really made difference when it comes to the quantity. That is, when the rainfall intensity is 2.5mm/min, the average runoff rate of the spoilbank which consisted of larger gravel was 1.14 times more than that of the spoilbank that consisted of smaller gravel. And the mean erosion rate of the spoilbank which consisted of larger gravel was 1.21 times more than that of the spoilbank that consisted of smaller gravel. What is more, the gap of both the total sediment yield and the runoff volume between these two types of spoilbank accorded with linear correlation with rainfall intensity significantly.(6) Engineering deposits have unique soil constitutions and complex conditions of underlying surface. So some hydrodynamic mechanisms that acquired by studying the traditionally two-dimensional slope are not applicable for a three-dimensional deposit. As a result, studying the hydrodynamic process of soil erosion caused by these engineering deposits is of great necessity. In this study, a type of engineering deposit had been selected—rolling compaction by construction machinery at the top of slope, and the hydrodynamic process of soil erosion originated from that was researched in inner-door rainfall experimental condition. Four kinds of artificial intensities(1.0 mm/min, 1.5 mm/min, 2.0 mm/min, 2.5 mm/min) and three gravel content(10%, 20%, 30%) were designed. The results show that the soil detachment rate have a significant linear function relationship with rainfall intensities and gravel content(mass ratio), and the relevance is extremely high(R2=0.919). So, the sediment yield can be figure out if only the rainfall intensity and the gravel content are clear. Hydraulic parameters like flow shear stress, stream power, unit stream power and unit energy of water-carrying section can be utilized to calculate the soil detachment rate, while the stream power is the best one among them. The power function relationship between soil detachment rate and the stream power is obvious(R2=0.884). This means that studying the hydrodynamic process of soil erosion caused by these engineering deposits in energy respect is better than in stress respect. By comparison, both the platform and the slope have a contribution to the total soil detachment rate of experiment engineering deposits, and the contribution of the platform is 5.0×10-6 kg/(m2·s).(7) A three-dimension engineering deposit has been designed according to the wild deposit proportionally. Four types of artificial intensities and three kinds of gravel content were devised to conduct the subsequent analysis of the relation under rainfall conditions. And a mathematical technique(Grey Relational Analysis) had been utilized to analyze the experimental data. The results indicated that:(1) The stream power and soil detachment rate were in a form of power function significantly, which consequently was the most suitable hydrodynamic parameters describing the hydrodynamic process;(2) Gravel content was not suitable to be treated as a variables to study the hydrodynamic process of soil erosion caused by tapered engineering deposit alone, when the artificial intensities was≥1.5mm/min;(3) When the gravel content was a fixed value, rainfall intensity was a decent variable to research the connection between hydrodynamic parameters and soil detachment rate. According to the results above, stream power can be treated as the most suitable hydrodynamic parameter to build the physical erosion model of the tapered engineering deposit in Northern Jiangxi Province. |
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