What are the different methods to find hydraulic conductivity?
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Hydraulic conductivity is the ease with which water moves through porous spaces and fractures in soil or rock. It is subject to a hydraulic gradient and affected by saturation level and permeability of the material. Hydraulic conductivity is generally determined either through one of two approaches. An empirical approach correlates hydraulic conductivity to soil properties. A second approach calculates hydraulic conductivity through experimentation.
1st Approach
TL;DR (Too Long; Didn't Read)
The small sizes of the soil samples handled in the laboratory are a point representation of the soil properties. However, if samples used in laboratory tests are truly undisturbed, the calculated value of K will represent the saturated hydraulic conductivity at that particular sampling point.
If not conducted properly, a sampling process disturbs the structure of the soil matrix and results in an incorrect assessment of actual field properties.
An inappropriate test fluid may clog the test sample with trapped air or bacteria. Use a standard solution of de-aerated 0.005 mol calcium sulfate (CaSO4) solution saturated with thymol (or formaldehyde) in the permeameter.
2nd Approach
The Empirical Approach
Calculating Conductivity
Calculating hydraulic conductivity empirically by selecting a method based on grain-size distribution through the material. Each method is derived from a general equation.
The general equation is:
K=(g ÷ v)_C_ƒ(n) x (d_e)^2
Where K = hydraulic conductivity
g = acceleration due to gravity;
v = kinematic viscosity;
C = sorting coefficient;
ƒ(n) = porosity function;
and d_e = effective grain diameter.
The kinematic viscosity (v) is determined by the dynamic viscosity (µ) and the fluid (water) density (ρ) as v=µ ÷ ρ.
The values of C, ƒ(n) and d depend on the method used in the grain-size analysis. Porosity (n) is derived from the empirical relationship n=0.255 x (1+0.83^U) where the coefficient of grain uniformity (U) is given by U=d_60/d_10. In the sample, d_60 represents the grain diameter (mm) in which 60 percent of the sample is more fine and d_10 represents the grain diameter (mm) for which 10 percent of the sample is more fine.
1st Approach
TL;DR (Too Long; Didn't Read)
The small sizes of the soil samples handled in the laboratory are a point representation of the soil properties. However, if samples used in laboratory tests are truly undisturbed, the calculated value of K will represent the saturated hydraulic conductivity at that particular sampling point.
If not conducted properly, a sampling process disturbs the structure of the soil matrix and results in an incorrect assessment of actual field properties.
An inappropriate test fluid may clog the test sample with trapped air or bacteria. Use a standard solution of de-aerated 0.005 mol calcium sulfate (CaSO4) solution saturated with thymol (or formaldehyde) in the permeameter.
2nd Approach
The Empirical Approach
Calculating Conductivity
Calculating hydraulic conductivity empirically by selecting a method based on grain-size distribution through the material. Each method is derived from a general equation.
The general equation is:
K=(g ÷ v)_C_ƒ(n) x (d_e)^2
Where K = hydraulic conductivity
g = acceleration due to gravity;
v = kinematic viscosity;
C = sorting coefficient;
ƒ(n) = porosity function;
and d_e = effective grain diameter.
The kinematic viscosity (v) is determined by the dynamic viscosity (µ) and the fluid (water) density (ρ) as v=µ ÷ ρ.
The values of C, ƒ(n) and d depend on the method used in the grain-size analysis. Porosity (n) is derived from the empirical relationship n=0.255 x (1+0.83^U) where the coefficient of grain uniformity (U) is given by U=d_60/d_10. In the sample, d_60 represents the grain diameter (mm) in which 60 percent of the sample is more fine and d_10 represents the grain diameter (mm) for which 10 percent of the sample is more fine.
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