Soil Properties - SR04-10094

9.2 Soil Properties

Besides the meteorological data, how representative the soil parameters are of the region

being modeled has a significant effect on FASST's ability to accurately predict the state

of the ground. At a minimum, the user must provide information concerning the number

of layers (maximum is 10), layer thickness, and the layer USCS (Unified Soil

Classification System) soil type. The soil parameters that FASST uses are

γd

Bulk density of dry material (g/cm3)

ρd

Intrinsic density of dry material (g/cm3)

θd

Volume fraction of solids

Emissivity (3.0100 m)

Quartz content

q

θof

Organic Fraction

Thermal conductivity of dry material (W/m⋅K)

kth

Specific heat of the dry material (J/kg⋅K)

C

Saturated hydraulic conductivity (cm/s)

Ksat

θr

Residual water content (vol/vol)

θmax

Maximum water content (vol/vol)

αvG

van Genuchten bubbling pressure head (cm)

van Genuchten exponent

nvG

Cone index/moisture content coefficient 1

c1

Cone index/moisture content coefficient 2

c2

Rating cone index/moisture content coefficient 1

c1

Rating cone index/moisture content coefficient 2

c2

Many of the above parameters are related. For instance, the bulk density (γd), mass per

total volume, is related to intrinsic density (ρd), mass per fractional volume of solids, in

the following manner γ d = θd ρd where θd is the volume fraction of the solids to the soil

as a whole. Remember also that the porosity, n, and void ratio, e, are related through

n= e

. In addition, the porosity is also a function of the volume of solids, θd, i.e,

(1 + e)

n = 1 θd.

The thermal conductivity of the bulk dry material (κdry) is related to the thermal

conductivity of the solids (κs) by

κ dry = κ s(1-n )κ a

n

(9.1)

where κa = 0.026 W/m⋅K is the thermal conductivity of air and n is the porosity.

Unfortunately, the thermal conductivity of the solids is seldom known. A different

approach, and the one used by FASST, is to calculate κdry based on (Farouki 1981):

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