The Study Of Macropore And Permeability Of Well Vegetated Slope Soils Based On CT Scans

Heavy rainfall in mountainous watershed is always followed by development of vegetated slopes instability, for its main reason is the ascension of the groundwater level caused by rainfall infiltration. Saturated permeability coefficient is a main parameter in evaluating the infiltration characteristics of soils. Macropore’s distribution law and structural characteristics are the key factors which influencing the permeability of soils. Hence, the research in the Macropore and the permeability of the vegetated slopes soils is very necessary. This paper takes the vegetated slopes soils in TOUZHAIGOU for research objects. Using the field investigation, indoor and outdoor tests test and sending sample-analysis to fully study the geological and climate features and the physical properties of vegetated slopes soils. CT scan and Image Processing applied here to obtain the distribution of macropores’size and its Shape Feature. Using cutting ring method to determine the saturated permeability coefficient, and compare it with predictive value of capillary tubes model. Concrete working contents and conclusions are in the following:(1) Making analysis on the geological survey, meteorological monitoring and physical properties of the soils in vegetated slopes, we can draw such conclusions: compared with the toe of slope, the source area gets a heavily rainfall and a lower temperature than it; the bulk density, dry density and particle specific gravity of the tested soil are smaller than the grassland, yet the bulk water content and the void ratio are bigger. The organic matter content is 6-10 times higher than that in agricultural soil; the root system in soil is mainly distributed in the surface layer within the scope of 50cm;bacteria occupies the majority of the microbes’type, the amount of the microbes changes with the depth and shows the decreasing trend; Quartz, Plagioclase and Montmorillonite are the mainly clay mineral of the tested soil, in specific samples Kaolinite can also be found;(2) Using CT scan and Image Processing, we get the macropore size distribution and its shape feature, which show that CT scan can be excellently applied to the analysis of micropore for its high-precision; macroporosity has a tendency to decrease with depth increasing; the number of macropore tends to decrease exponentially with aperture level increasing; soil macropore tends to have a narrow shape with the soil depth increasing; the larger the macropore equivalent diameter, the rougher its outline.(3) Through the observation of preferential flow, measuring of saturated permeability coefficient and its contrastive analysis, we draw the conclusion: the main channel of preferential flow includes the hole of animals, interval between root and soil, dry shrinkage crack and rotten root channels; the saturated permeability coefficient which tested by cutting-ring method has a tendency to decrease with depth increasing; there is a certain deviation between actual value and predicted value of the saturated permeability coefficient measured by the capillary tubes model, but both of them are in the same order of magnitude; the revised capillary tubes model has a significantly accuracy, the mean square error of predicted value after amendment and measured value decreases from 0.64 to 0.41.