Environmental Engineering Reference
In-Depth Information
w
w
C c / G s
C s / G s
10 6
10 6
y aev
y aev
Logarithmic soil suction
Logarithmic soil suction
(a) Slurry soil specimen
(b) Highly consolidated specimen
w
C s / G s
C c / G s
p c
10 6
y aev
Logarithmic soil suction
(c) Normally consolidated specimen
Figure 5.53 Typical shapes for SWCCs (i.e., gravimetric water content) of a soil subjected to
various stress histories (after Pham, 2005).
Several typical forms for the gravimetric water content ver-
sus soil suction curve are shown in Fig. 5.53. A clay soil, for
example, can be subjected to different stress histories with the
result that the SWCC changes; however, the general form of
the equation remains the same. A slurry soil will be highly
compressible in the low-effective-stress range. Preconsoli-
dated soils may have been subjected to a stress state that is
higher than the air-entry value of the soil. Most originally
proposed empirical equations for the SWCC are sigmoidal in
shape. Consequently, these equations cannot adequately rep-
resent the SWCC in the region below the air-entry value since
the equations are asymptotic to a horizontal line. The sig-
moidal equations are more suitable for best fitting the degree
of saturation form of the SWCC. It is prudent to have a
curve-fitting equation that can be applied to soils that exhibit
significant volume change (Mbonimpa et al., 2006).
w 2 ( y )
S 1
w sat
w aev
This line presented by
equation: w 1 ( y )
t 1
w 3 ( y )
S 2
t 2
w r
S 3
y aev
1
y r
10 6
y (kPa)
Logarithmic soil suction
Figure 5.54 Typical SWCC for a soil that changes volume along
with a designation of the variables required to define the curve
(after Pham, 2005).
S 3 . The water content at a soil suction of 10 6 kPa is assumed
to be equal to zero (Fredlund and Xing, 1994). Parameters t 1
and t 2 can be used to control the transitions between various
portions of the SWCC. Three equations correspond to the
three sloping lines that can be written as three mathematical
functions [i.e., w 1 (ψ), w 2 (ψ) , and w 3 (ψ) ]:
5.6.1 SWCC Equation with Meaningful Parameters
for Entire Suction Range
It is useful to have SWCC equations written in terms of vari-
ables that have physical significance (e.g., air-entry value;
residual soil suction; residual water content; maximum slope
of the SWCC). Such an equation is particularly useful when
conducting sensitivity studies where the fundamental prop-
erties of the soil can be varied. The basic properties of
a SWCC are shown in Fig. 5.54. Most SWCCs can be
represented by three straight lines with slopes of S 1 ,S 2 , and
S 1 log ψ
1
S 3 log ( 10 6 )
w 1 (ψ)
=
w s
=
+
(S 1
S 2 )
×
log aev )
+
(S 2
S 3 ) log r )
S 1 log (ψ)
(5.64)
 
Search WWH ::




Custom Search