Environmental Engineering Reference
In-Depth Information
w
All pores in soil
Collapsible pores
Noncollapsible pores
Drying-wetting of
collapsible pores
C c /G s
Drying-wetting of
noncollapsible pores
w c / (
ψ
)
w r
ψ r
Logarithmic soil suction (kPa)
10 6
log(
ψ
)
Figure 13.38 Illustration of gravimetric water content for collapsible and interconnected pores
along initial drying process (from Pham, 2002).
An equation for the SWCC of collapsible pores, w c (ψ) ,
can be obtained directly by using the curve-fitting parame-
ters used in Eq. 13.109:
Similarly, the unloading-reloading compression index of
the group of pores having a logarithmic soil suction ξ can
be calculated as follows:
d C c
w sat
w r a
(13.117)
a
( 10 ξ ) b
C c
G s
C s ab ln ( 10 )( 10 ξ ) b
( 10 ξ ) b
+ a
w c (ψ) =
C s (ξ) =−
log (ψ)
=−
+ a 2
(13.120)
ψ b
+ a
where:
where:
a, b, w r
=
curve-fitting parameters that can be obtained
by best-fitting Eq. 13.109 to the measured
SWCC.
C s
=
unloading-reloading index of the soil at saturation.
An equation for the reference DPD of the soil can be
obtained by differentiating both sides of Eq. 13.115 and
then substituting Eq. 13.117 into the new formulation:
13.6.4.4 Summary of Compression Indices of Pores
The virgin compression index of a group of noncollapsible
pores having an air-entry value of ξ can be calculated by
substituting Eq. 13.116 into Eq. 13.114:
C c (ξ) =− d G s w c ( 10 ξ )C c /(e sat C c ξ
d [ w (ψ) ]
aC c
ψ b
f d (ψ) =−
G s ψ ln ( 10 )
(13.121)
+ a
where:
w r G s )
w (ψ) =
gravimetric water content along the initial drying
curve of an initially slurry soil.
(13.118)
Substituting Eq. 13.117 into Eq. 13.118, gives
An equation can be derived for the virgin compression
index of air-filled pores in a manner similar to that used
for the compression indices for water-filled pores. The dried
virgin compression index of a group of pores having an
air-entry value ξ can be written as follows:
d C c
a
( 10 ξ ) b
C c ab ln ( 10 )( 10 ξ ) b
( 10 ξ ) b
+ a
C c (ξ) =−
=−
+ a 2
(13.119)
where:
C cd ab ln ( 10 )( 10 ξ ) b
( 10 ξ ) b
C cd (ξ) =−
(13.122)
+ a 2
C c =
virgin compression index of the soil under satu-
rated loading and
where:
a, b
=
curve-fitting parameters obtained from best fitting
the SWCC of the soil from (initial) slurry condi-
tions (Eq. 13.109).
C cd
=
virgin compression index of the soil under dried
conditions.
 
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