Estimation of Unsaturated Hydraulic Conductivity of Granular Soils from Particle Size Parameters

• Main Authors: Ji-Peng Wang, Pei-Zhi Zhuang, Ji-Yuan Luan, Tai-Heng Liu, Yi-Ran Tan, Jiong Zhang
• Format: Article
• Language: English
• Published: MDPI AG 2019-08-01
• Series: Water
• Subjects: hydraulic conductivity; unsaturated granular soil; relative permeability; grain size distribution; porosity
• Online Access: https://www.mdpi.com/2073-4441/11/9/1826

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&#8217;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 <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>d</mi> <mrow> <mn>10</mn> </mrow> </msub> <mo>&nbsp;</mo> </mrow> </semantics> </math> </inline-formula>&gt; 0.02 mm and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>C</mi> <mi>u</mi> </msub> </mrow> </semantics> </math> </inline-formula> &lt; 20, in which <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>d</mi> <mrow> <mn>10</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula> is the grain diameter corresponding to 10% passing and <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>C</mi> <mi>u</mi> </msub> </mrow> </semantics> </math> </inline-formula> is the coefficient of uniformity (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>C</mi> <mi>u</mi> </msub> <mo>=</mo> <msub> <mi>d</mi> <mrow> <mn>60</mn> </mrow> </msub> <mo>/</mo> <msub> <mi>d</mi> <mrow> <mn>10</mn> </mrow> </msub> </mrow> </semantics> </math> </inline-formula>). 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.