| Erosion of engineering piles is different from traditional slopes,owing to lacking organic matter,scatter material composition and special form.However existing studies are mainly focused on the tradition slopes or the short-slope piles,so that the erosion processes of the engineering deposits in the field can't be studied accurately.Gravel is always an important part of the engineering piles which may change the physical properties of the piles and cause particular erosion characteristics.As a result,studying the erosion processes of three-dimensional engineering piles with the same degree with that in the field is necessary.In this paper a self-made platform was used to simulate the three-dimensional pyramidal engineering piles and an indoor artificially simulated rainfall experiment under different rainfall intensities was carried out to study the law of erosion and runoff of engineering piles with different mass percentage of gravel(0%,10%,20%,30%,40%).The results show that :(1)For the three-dimensional engineering piles which the composition material is loam:both the rainfall intensity and the rill have significant impacts on the volume of runoff and the rate of erosion.The tendency of runoff and erosion is different with the rainfall intensity;The width of rill shows the variation tendency of “Augmentation-Mutation-Stability”,the depth of rill shows an increase in volatility.The length of rill which has obvious relevance to the rate of erosion can represent the process of rill well.In the initial runoff(1~10 min),the rainfall intensity has a small influence on the rate of erosion.As the increase of rainfall intensity,the erosion rate shows a relatively smooth curve.When the runoff time is more than 10 minutes,the erosion rate is affected by the rainfall intensity significantly,and the erosion rate shows an exponential increasing trend with the increase of rainfall intensity.There is an obvious exponential relationship between the total amount of erosion and the rainfall intensity according to the experimental data.(2)For the pyramidal engineering piles with grave which the composition material is loam: The runoff rate and velocity of flow increase with the increase of rain intensity and decrease with the increase of gravel content both of them show a trend of “increase first and then slowly increase to final stable state” with time.The runoff is in laminar and subcritical flow state,and Reynolds number and Froude number increase with the increase of rain intensity and decrease with the increase of gravel content.When the rainfall intensity is 1.0mm/min the erosion rate firstly increases rapidly and then gradually becomes stable,when the rainfall intensity is greater than 1.5 mm/min the erosion rate shows a trend of continuous growth,among which when the rainfall intensity are 2.0 and 2.5 mm/min the erosion rate increase abruptly in the middle and late test process.The total amount erosion shows an exponential increasing trend with the increase of rainfall intensity and a logarithm decreasing trend with the increase of gravel concentration.There is a significant power function relationship between erosion detachment rate and shear stress,stream power,unit flow power and unit energy of water-carrying among which stream power has the best correlation with erosion detachment rate therefore it is the optimal factor to describe soil erosion.The rill occurring time advanced and the length,width,depth of rill increased with rainfall intensity increasing,while the rill occurring time is delayed,the depth and width of rill decrease gradually with the increase of gravel concentration in the same rainfall intensity.(3)For the engineering piles with grave which the composition soil type is clay:runoff rate show variation tendency of “Rapid increase-slow growth-tending to stabilize”.When the rain intensity is low the runoff rate is increasing with increase of gravel concentration for pyramidal engineering piles and and the gap is small for two-dimensional engineering piles.For the high rain intensity the runoff rate is decreasing with the increase of gravel concentration,when the stacking form is two-dimensional plane runoff show a tendency of increase first and then decrease with the increase of gravel concentration.The erosion rate is increasing firstly and the tending to stabilize when the stacking form is coinform or decreasing undulate when the stacking form is plane.The effect of gravel on erosion is “threshold” when the gravel concentration is less than threshold the amount of erosion is increasing and then decreasing.The threshold for pyramidal engineering piles is 20%,for two-dimensional engineering piles is 30%.Shear stress,stream power and unit energy of water-carrying all have a significant linear relationship with denudation rate,among them the stream power's relationship and the goodness of fit is the best.(4)For the engineering piles with grave which the composition soil type is sandy soil:runoff rate shows a steady trend after a gradual increase and increases as the rain intensifies.For the pyramidal engineering when the gravel concentration is less than 20 percent runoff rate is decreasing with the increase of gravel and then increasing.The erosion rate is small at the beginning of runoff and then increases suddenly,with the increase of gravel content the erosion rate is decreasing.For the two-dimensional engineering piles there is no significant difference in runoff among gravel contents.The erosion rate shows a trend of “Mine-Stability-Addition-Stability”.At the stage of reduction and first stabilization,the difference of erosion rate among gravel contents is small after that,the erosion rate of the slope surface without gravel is obviously higher than that with gravel.The total amount of erosion increases with the increase of rainfall intensity and decreases with the increase of gravel content when the rainfall intensity is the same.(5)Revising the morphological factor of non-incoming water engineering piles,the final determined form factor is 0.85.The model is verified by the data obtained from the indoor simulation test and the field runoff plot,the prediction accuracy of the model is confirmed to the consistent with the actual situation. |
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