Study On Spatial Distributions Of Rock Fragments In Purple Soils On Hillslopes And Its Water Infiltration Properties

The purple soil with rock fragments is widely distributed in hilly area of southeast China, and gravel spoil generate by construction of various development and construction projects, which are very important soil erosion region. Study and understanding the erosion rules of soil with rock fragments, is very significant for soil erosion prediction of the dregs pile and soil and water conservation planning of rocky hills and mountains. In this paper, study on Wangjiaqiao small catchment Shuitianba small town Zigui County, through fields investigation of 2 complete the hillslope and laboratory simulation, research the distribution of gravel on the slope section and typical soil profile, simulate and discuss the different rock fragment contents, sizes and fine soil bulk on the soil water infiltration. The main results are as followings:(1) Upword the hillslope, total content of gravel are increased, Gravel content of the grain size increased with the particle size, and then decreased. The contents of rock fragments (20-76mm) are bigger, between 30%-75%, followed by the rock fragments(10-20mm). In the profile,The relative content of rock fragments the general distribution:Content of rock fragments decreased with the soil depth of the bottom and lower hillslope; Content of rock fragments increased with the soil depth of top and upper hillslope. Surface rock fragments is smaller,due to the human activity removing part of rock fragments in the farming.(2) Different rock fragment contents, sizes and fine soil bulk density have different process of purple soil water vertical movement. bulk density 1.35g/cm3 soil-stone mixture, both of cumulative infiltration and wetting front decreased with the increases of the stone contents. Different bulk density of the soil containing gravels, both of cumulative infiltration and wetting front firstly decreased with the increases of the stone contents, and then increased. Same rock fragments contents and sizes of the soil containing gravels.(3) Soil-stone mixture Saturated hydraulic conductivity decreased with the rock fragment content to minimum values for Rc=20%, and then increases into the binomial relationship with gravel content. Saturated hydraulic conductivity increased with the rock fragment sizes increases. Saturated hydraulic conductivity decreased with the bulk density increases.(4) Interlayer soil-stone mixture, both of cumulative infiltration and wetting front decreased with the increases of the stone contents or sizes. When the gravel size were between 20-76mm, Saturated hydraulic conductivity decreased with the rock fragment content to minimum values for Re=20%, and then increases. When the gravel size were between 10-20mm, saturated hydraulic conductivity decreased with the rock fragment content to minimum values for Rc=30%, and then increases. Interlayer rock fragment total infiltration decreased with the increases of the stone sizes. Interlayer rock fragment promoted water infiltration.(5) bulk density 1.35g/cm soil-stone mixture,Comparing to the homogenous soil, Moisture content decreased with the increases of the stone contents and diffusivity is smaller. Different bulk density of the soil containing gravels, Moisture content increased with the rock fragment content to minimum values for Rc=10%, and then decreases diffusivity is bigger.