Abstract
Loess is very widely distributed, and the unsaturated hydraulic conductivity of loess is related to many engineering issues. To determine the unsaturated hydraulic conductivity of remoulded loess more conveniently and at a lower cost, filter paper test and soil column seepage test were carried out. The results indicate that in the one-dimensional soil column seepage process, the unsaturated hydraulic conductivity of loess increases with the increase of the volumetric water content, and as the seepage time continues, the unsaturated hydraulic conductivity of loess from the top to the depth of 40 cm gradually becomes uniform. The changes in the microstructure indicate that the collapsible settlement will occur during the seepage process, which will change the pore structure of loess, thereby reducing the unsaturated hydraulic conductivity of the underlying loess. Compared with the experimental results, the soil hydraulic conductivity curve (SHCC) obtained by the van Genuchten–Mualem model (VG–M model) underestimates the magnitude of unsaturated hydraulic conductivity in the part with a low volumetric water content (< 20%). and the Childs and Collis-George model (CCG model) has more consistent results with the experimental results, because it is based on more segments of the soil–water characteristic curve (SWCC).
Highlights
The unsaturated hydraulic conductivity of soil is one of the primary soil parameters, which is directly related to many engineering issues, such as landslides and foundation settlement caused by rainfall infiltration, design of irrigation and drainage system, and environmental risk assessment (Fredlund and Rahardjo, 1993; Gribb, et al, 2004; Rahimi, et al, 2010)
The indirect method refers to obtaining unsaturated hydraulic conductivity, remoulded loess, filter paper method, hydraulic conductivity through empirical models and statistical models, which are mainly based on saturated hydraulic conductivity (Gardner, 1958), pore size distribution of the soil (Kunze, et al 1968; Rosas, et al, 2015), and soil-water characteristic curve
The results obtained by the filter paper method are calibrated by Eq (7) and plotted in the suctionwater content relationship diagram
Summary
The unsaturated hydraulic conductivity ( termed as unsaturated permeability coefficient) of soil is one of the primary soil parameters, which is directly related to many engineering issues, such as landslides and foundation settlement caused by rainfall infiltration, design of irrigation and drainage system, and environmental risk assessment (Fredlund and Rahardjo, 1993; Gribb, et al, 2004; Rahimi, et al, 2010). The soil in nature (such as loess) is mostly in an unsaturated state, and the hydraulic conductivity of unsaturated soil is not a constant, but a function of suction or water content. The relationship between unsaturated hydraulic conductivity and suction or water content is usually expressed in the form of K function expression or soil hydraulic conductivity curve (SHCC). There are many methods to determine unsaturated hydraulic conductivity, but generally it can be summarized into direct and indirect methods. The indirect method refers to obtaining unsaturated hydraulic conductivity, remoulded loess, filter paper method, hydraulic conductivity through empirical models and statistical models, which are mainly based on saturated hydraulic conductivity (Gardner, 1958), pore size distribution of the soil (Kunze, et al.1968; Rosas, et al, 2015), and soil-water characteristic curve (van Genuchten, 1980; Ye, et al, 2014)
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