k	Hydraulic permeability (m/s)
kr	Relative hydraulic conductivity
$k_r{}^{*}$	Proposed relative hydraulic conductivity of compacted bentonite
ksat	The saturated hydraulic conductivity (m/s)
kunsat	The unsaturated hydraulic conductivity (m/s)
Se	The effective saturation
θ	The actual volumetric water content
θr	The residual volumetric water content
θs	The saturated volumetric water content
α	The constant parameter in Mualem [54]
μ	A dimensionless number in Burdine [31]
Ψ	Suction of soil/bentonite(MPa)
Ψd	The air entry value (MPa)
λ	A fitting factor related to pore-size distribution
Cs	Shape factor
τ	Tortuosity
γw	Unit weight of water (N/m3)
η	Viscosity of water (Pa∙s)
SA	Specific surface area (m2/kg)
Φ	Porosity
ρd	Dry density of soil (kg/m3)
Atot	Total specific surface area (m2/kg)
n	The number of TOT layers of per particle
N	Total number of TOT layers of bentonite sample
Aext	External specific surface area of bentonite (m2/g)
As	The surface area of a single TOT layer
msi	Mass of one particle (kg)
msmectite	Mass of smectite (kg)
ms	Mass of solid (kg)
b C	A constant related to water adsorption rate A correction term
ω	Water content (kg/kg)
ρw	Density of water (kg/m3)
mw	The mass of water (kg)
Vt	Total volume of soil sample (m3)
Vw	Volume of total water in soil (m3)
${\rho }_d^s$	Dry density of smectite (kg/m3)
dTOT	Thickness of TOT layer (9.5 Å)
dt	Basal spacing (Å)
hw	Total interlayer water thickness of soil
Vimw	Micro pore volume/volume of interlayer water
Ve	Macro pore volume/effect pore volume
Vs	Volume of solid (m3)
diw	Interlayer water thickness between two TOT layers
Φmacro	Macro porosity (Effective porosity)
Φmicro	Micro porosity (Interlayer porosity)
ρs	Density of the solid (kg/m3)
ρi	Density of the non-smectite minerals or impurities (kg/m3)
Gs	Specific gravity of clay
Xsm	The mass fraction of smectite in the bentonite
Le	Effective path length of flow
L	Sample length
ref	The reference case in which measurements are available
β	A fitting factor between Φ and Ψ in Pham et al. [92]
σ	Coefficient related to porosity and size of pore
Xhs	Mole fraction of hydrated smectite
Msm	Molar mass of dry smectite (Kg/mol)
ζc	The number of moles of waters in the interlayer adsorption or desorption reaction
υil	The molar volume of the interlayer water (m3/mol)
a, m	Curve-fitting parameters by van Genuchten [24]
nmax, nmin	The maximum and minimum number of TOT layers of bentonite particle respectively