Abstract
Estimation of unsaturated hydraulic conductivity could benefit many engineering or research problems such as water flow in the vadose zone, unsaturated seepage and capillary barriers for underground waste isolation. The unsaturated hydraulic conductivity of a soil is related to its saturated hydraulic conductivity value as well as its water retention behaviour. By following the first author’s previous work, the saturated hydraulic conductivity and water retention curve (WRC) of sandy soils can be estimated from their basic gradation parameters. In this paper, we further suggest the applicable range of the estimation method is for soils with d10 > 0.02mm and Cu < 20, in which d10 is the grain diameter corresponding to 10% passing and Cu is the coefficient of uniformity (Cu=d60d10). The estimation method is also modified to consider the porosity variation effect. Then the proposed method is applied to predict unsaturated hydraulic conductivity properties of different sandy soils and also compared with laboratory and field test results. The comparison shows that the newly developed estimation method, which predicts the relative permeability of unsaturated sands from basic grain size parameters and porosity, generally has a fair agreement with measured data. It also indicates that the air-entry value is mainly relative to the mean grain size and porosity value change from the intrinsic value. The rate of permeability decline with suction is mainly associated with grain size polydispersity.
Highlights
Unsaturated hydraulic conductivity is an important parameter for the study of water flow in the vadose zone, unsaturated seepage process, underground waste isolation etc.measuring unsaturated hydraulic conductivity values of different sediments could be timeand cost-consuming
To predict the saturated hydraulic conductivity of granular soils based on particle size distribution, the different estimation methods may be more suitable for granular soils with a unimodal shape pore size distribution
Based on the estimation method proposed by Wang et al [8], the saturated hydraulic conductivity of sandy soils can be estimated from basic soil gradation parameters
Summary
Unsaturated hydraulic conductivity (or permeability) is an important parameter for the study of water flow in the vadose zone, unsaturated seepage process, underground waste isolation etc. It is widely accepted that using grain size distribution parameters can estimate its saturated hydraulic conductivity [4,5,6,7,8] and water retention curve [9,10,11,12]. The method shows the best prediction accuracy among the classic methods They have developed a method to estimate water retention behaviour of sandy soils after van Genuchten’s closed-form equation [12], which is related to the unsaturated permeability. As an important new contribution we will consider the porosity variation effect on the air-entry value of relative permeability and water retention curve, which will further improve the model accuracy. The effect of key gradation parameters and porosity variations on unsaturated hydraulic conductivity properties will be discussed
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