Experimental Study Of Effects Of Column Size And Textural Layers On Saturated Hydraulic Conductivity

Soil saturated hydraulic conductivity(Ks)is one of the most important soil physical parameters that can be used to characterize soil physical properties, estimate soil unsaturated hydraulic conductivity as this parameter is an important input for hydrological, as well as for crop models, including those that use a capacitive water balance module. The experimental determination of soil saturated hydraulic conductivity indoor is the basic part of soil physical experiment that commonly used to provide the essential parameter or numerical reference for other experiments. While the determination of Ks is susceptible to the length of measure duration, experiment method, sampling size and other factors, which would affect its validity and reference value. Therefore, this dissertation used different texture soil to simulate the effect of column size, layered soil structure and particle diameter on soil saturated hydraulic conductivity at laboratory scale. The main results and conclusions were as follows:1 The value of soil saturated hydraulic conductivity reduced with time, it reduced rapidly in the first 20 minutes, and then reduced slowly. Compared with other column sizes, the largest reduction occurred when the 5cm diameter columns were used for both tested soil types. The reduction of disturbed sandy loam saturated hydraulic conductivity measurements was greater than disturbed clay loam throughout the entire experiment time series.2 The changing of saturated hydraulic conductivity of disturbed sandy loam with soil column diameter(CV=22.94%) was much bigger than disturbed clay loam(CV=2.6%). The Ks of both soil types showed a trend of slightly increasing with the increase of column diameter, but the increasing degree decreased gradually, and the disturbed sandy loam had a larger increase. Column wall effect can be used to explain the above phenomenon, and the column cross sectional area per wall length can be used as a variable to illustrate the effect quantitatively.3 Both the layer numbers and layering method of layered soil could affect the effective soil saturated hydraulic conductivity(Keff). For both soil and glass bead, the discrepancy of Keff of different two-layered structures was significant(p<0.05), which mainly lied in the texture difference between the upper and lower layers, while the up/down location had no significant effect on Keff. For the triple-layered columns and multi-layered with two texture soil columns, the Keff of different layered structure was significantly different(p<0.01). For multi-layered soil structure with two soil textures, the Keff had a tendency to increase with the layer number.4 The applicability of effective saturated hydraulic conductivity formula weakened as the internal structure of layered soil column became more complicated. It was obtained that finer texture or particle size had greater influence on the Keff of soil or glass bead columns by nonlinear simulation of the experiment data. For the triple-layered columns, the influence coefficients by the distribution of the three layers as well as the textures differed significantly rather than the glass bead columns. Parameters fitted by soil experiment results showed poor applicability to glass bead columns, which indicated that Keff of layered soil columns affected by finer texture. It was not only related to the particle diameters but also to the properties of clay in soil.5 For the sandwich glass bead column structures with different interlayer thickness, the cases of sandwiched the coarser particles between the finer particles showed a higher Keff than sandwiched the finer between the coarser ones. The sandwich structure with a coarser particle interlayer showed a higher Keff than that with finer interlayer. For all sandwich structures, the Keff increased when the thickness of interlayer increased equally.