Rainfall Infiltration Characteristics Of Soil In Well Vegetated Slope

As landslide disasters are increasingly serious with global warming, the study of slope instability is imminent. The permeability coefficient, an important parameter of evaluating soil nature in well vegetated slope, is of great significance to study stability of slope. Based on situ double-loop infiltration test, laboratory ring test and physical properties determination test on well vegetated slope soil, this article verify the feasibility of double-loop infiltration test, and measure the soil parameters such as saturated permeability coefficient, infiltration curve, root content, organic matter, particle composition, porosity ratio and moisture content within one meter depth. This study analyzes rainfall infiltration characteristics and its influence factors, and relationships between soil permeability and properties.A relative simply method, which derived from Brooks and Corey model, is described in this paper for estimating the unsaturated hydraulic conductivity. By this mean unsaturated hydraulic conductivity be calculated from saturated hydraulic conductivity, gravimetric water content and the pore size distribution exponent, which estimated by Bloemen’s equation from organic matter content and granular composition. At the same time, the model results compared with the HYDRUS-2D calculated value. With comparing the model results and the HYDRUS-2D calculated value, this method be proved that it has high relative precision and is applicable to well vegetated slope soils. Also, direction of further optimization is put forward in this paper. Researches show that:(1) With the higher vegetation coverage in well vegetated slope, the organic content and the spatial variability of water content become greater, the natural density, dry density, and specific gravity get smaller, the void ratio turn larger.(2) The infiltration curve fluctuations of well vegetated slop is large, speed after infiltration began is more greater than the steady infiltration rate, the interval time of reaching stability for curve is commonly2-3hours. As the infiltration curve of laboratory ring test is relatively flat, the reaching stability time about one hours, and the difference between start velocity and stable velocity is small.(3) With strong suction, strong storage and high permeability properties, ability to accept rainfall of lasted30minutes,60minutes and stable are greater than the rainstorm intensity. Shallow soil permeability is sensitive to vegetation coverage, void ratio, root content and organic matter content.(4) As the permeability of shallow slope appears to decrease, in which there is a increase with depth larger after first decrease, the soil above minimum permeability turns phenomenon of stagnant water.(5) This paper introduces the formula of unsarurated permeability coefficient estimation model, which optimized from BC model, considering the effect of organic matter on the permeability. The estimating formula is suitable for the well vegetated slope, and value of root mean square error between the formula and HYDRUS-2D is100.64cm/s. So the formula has high precision and improves the computational efficiency of unsaturated permeability coefficient.