Research On Regularity And Estimate Model Of Soil And Water Loss In Pile Body Of Development Construction Project

As lots and different pile bodies were produced by the rapid development of large-scale construction projects had caused soil and water loss which did not only become one of the important sources to increased water and soil loss, but also become the hot and difficult plot in this study field. The pile body of development construction project was formed during construction, with the characteristic of stacked loose, shorter slope length, steeper slope. It often reached the natural angle of accumulation materials, complex and diverse composition, variation in particle size, and different gravel in it. These made it quite different from traditional farming land. Compared with the traditional abandoned and agricultural land, soil and water loss which was caused by pile body of development construction projects belonged to man-made accelerated erosion, and produced serious hyperconcentrated flows more easier. Landslides and other disasters happened in rainstorm resulted in certain difference of the regularity of soil and water loss with farmland. Currently, the research of prediction model on the soil and water loss by pile body of development construction project was less, same as the necessary scientific basis to predict the amount of soil erosion of soil and water conservation programs, which lagged far behind the actual needs of production. Therefore, on the basis of preliminary large numbers of experiment, took the erosion characteristics of pile body under different terrain conditions in sand area and clay area had been studied by indoor artificial rainfall test. According to the relationship between erosion amount and influence factors of pile body, the mechanism of pile body soil erosion was clarified and each model parameter was got and revised, and established estimate model of soil and water loss in pile body of development construction project finally. Providing supporting for soil and water conservation programs and soil erosion monitoring, and improvement of soil erosion model research. It has important scientific significance and value of production. According to the experiment data, the main conclusions were as follows.(1) Characteristics of erosion parameters by rainfall event of pile body in sand area and clay area showed tendency of sediment concentration along with runoff time was relatively stable after descending and then significant fluctuations in sand area, while decreased in first 3min and then stabilized with time in clay area. There existed a critical value gradient for influence of sediment concentration at 25 degree of slop. The Reynolds numbers was less than 300 in areas all plot, and gave priority to laminar flow, the Froude numbers varied within 0.5-2.0, belongs to slow flow. Erosion rate showed significant correlations with stream power, hydrodynamic shear stress and cross-section specific energy.(2) The runoff producing time showed a decreasing trend after the first increment with gravel content increasing in loam area, and reached the minimum when gravel content was 30%, and the average runoff rate was the least under this gravel content. It was a significantly negative linear correlation between the average velocity and gravel content,the average sediment concentration in soil with gravel content could reduced 21.1%~61.2% than pure soil.(3) Under the same gradient and slope length(25°, 5m), runoff yield in loam area faster than clay area, while sand area needed more time to runoff. The order of average runoff rate for pile body was loam area, clay area, sand area. Average sediment concentration in pure soil was bigger than soil with gravel content for pile body in sand and loam area, its increased range was 63.3%~379.5% along with rainfall intensity.(4) The average runoff velocity showed decreasing linear along with gravel content under different gradient in loam area. Average runoff rate decreased about 24.5%~33.0% along with gradient increasing. Average erosion rate in soil with gravel content was only 31.5%~65.0% than pure soil. Erosion amount decreased 34.3%~65.1% when gravel content increased. When the slope length was different, average runoff rate increased about 51.6%~314.2% along with slope length increasing under different slop length, and it decreased 3.0%~11.8% in gravel content than pure soil. Erosion amount decreased along with gravel content increasing, which was 1.5-2.6 times in pure soil than soil with gravel content.(5) The standard of unit plot and each factor of model definition was proposed for pile body of development construction project, it refers the pile body was continuous loose, unfarmed, and nudity under gradient of 25o, slope length of 20 m. Defined the soil erodibility as earth and rock erodibility factor T, which means the erosion amount by unit rainfall erosivity under the standard of unit plot.(6)Analysis the mechanism of soil and water loss, it showed the erosion amount would 2.1-13.7 times with rainfall intensity increasing. The erosion amount decreased along with gravel content increasing in sand area and loam area. There existed a critical gradient about 25°, which affected erosion amount. There was a significant power function between erosion amount and slope length, it could be increased about 23.4%~159.4% with slope length increasing.(7) According to definition of gradient and slope length factor, calculated the value of gradient factor were 0.6319,1.0000,0.9157,1.5147, which belonged to gradient for 15°,25°,30°,35°, respectively. And the value of slope length factor were 0.3051, 0.4837, 0.5355,0.6692 and 1.0000, which belonged to gradient for 2.72 m, 4.53 m, 5.89 m, 10.88 m and 20.00 m, respectively. It also gave the equations for gradient and slope length factor calculation for pile body of development construction project, and their exponent were 0.880 and 0.553, respectively. The value of earth and rock erodibility factor were 0.152, 0.108, 0.073 and 0.062 t·km2·h/(km2·MJ·mm), which belonged to gravel for 0%, 10%, 20% and 30% in sand area, respectively, while 0.054, 0.034, 0.029, 0.018 t·km2·h/(km2·MJ·mm) and 0.042, 0.036, 0.027, 0.020 t·km2·h/(km2·MJ·mm), which belonged to loam area and clay area, respectively. The earth and rock erodibility factor decreased with gravel content increasing, and showed a linear relationship between them. The earth and rock erodibility factor in sand area could be 2.8 and 3.6 times than loam area and clay area under pure soil.(8)The estimate model of soil and water loss was established based on the USLE in pile body of development construction project first time. In addition, rainfall erosivity R, earth and rock erodibility factor T, the value of gradient factor S and value of slope length factor L indicated the model, and completed the model validation.