Soil-Water Characteristic Curves for Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 193

approach saturated conditions under near-zero confinement.
Dimensionless gravimetric water content can be written in
terms of the individual measured mass values as follows:

test and (ii) the volumetric water contents are redefined at
each stage of applied suctions.
Normalized gravimetric water content ng has the amount
of water in the soil normalized between residual water con-
tent and saturated water content:

w
w s =

M w /M s
M w 0 /M s

dg = (5.5)

−

w w r

ng =

(5.8)

where:

w s − w r

M w 0 = mass of water in the saturated soil at the start of

the test,

where:
w r = residual gravimetric water content.

M s = mass of the soil solids, and

M w = mass of water at any point under consideration.

Normalized volumetric water content form nv has the
amount of water in the soil normalized between the residual
volumetric water content and the initial saturated volumetric
water content:

Dividing the top and bottom of Eq. 5.5 by the unit weight
of water, γ w , allows dimensionless water content to be writ-
ten in terms of volumes:

θ − θ r

nv = (5.9)

M w /γ w
M w 0 /γ w =

V w
V w 0

θ s − θ r

dg = (5.6)

where:
θ r

where:

= residual volumetric water content.

V w 0 = volume of water in the saturated soil at the start

of the test. Normalized water contents isolate physical soil behavior

between saturated conditions and residual water content con-
ditions. Figure 5.7 shows a typical data set for a sandy soil
plotted in terms of dimensionless water content and normal-
ized water content. Residual conditions generally reflect a
significant change in the behavior of the soil. For example,
the permeability function appears to describe the hydraulic
head flow of water through an unsaturated soil as long as
the water content is greater than the residual water content
(Brooks and Corey, 1964). Vapor flow begins to dominate
moisture flow at soil suctions higher than residual suction
conditions. Both the dimensionless and normalized water
content forms of the SWCC serve a useful purpose in the
interpretation of SWCC data and the computation of unsat-
urated soil property functions.

Dimensionless volumetric water content dv can be writ-
ten in equation form by dividing any water content by the
volumetric water content corresponding to initial (saturated)
conditions:

θ
θ 0 =

V w /(V v + V s )

dv =

(5.7)

V w 0 /(V v + V s )

Dimensionless gravimetric and volumetric water contents
can be used in either decimal or percent form. Dimensionless
gravimetric and volumetric water contents are equivalent in
magnitude. Dimensionless water contents are also equal to
the degree of saturation S of the soil provided (i) there is
essentially no deformation of the soil during the laboratory

Figure 5.7 Data from a sandy soil plotted in terms of dimensionless water content and normal-
ized water content.