Environmental Engineering Reference
In-Depth Information
Figure 15.17
Effect of initial degree of saturation on pore pressure predictions using Hilf (1948)
analysis.
0
Computed curve of
Δ
2
n
versus
Δs
y
4
Saturation pressure
6
8
Hilf's equation
n
versus
u
w
Δ
Δ
10
12
Consolidation data
Δ
n
versus
Δ(s −
u
w
)
45
°
14
0
5000
10,000
15,000
20,000
25,000
Overburden pressure (
s
y
), kPa
Stress, kPa
Figure 15.18
Plots of stress components versus volume change
for Hilf (1948) analysis.
Figure 15.19
Relationship of nonlinear pore-water pressure ver-
sus total stress derived for Hilf (1948) analysis.
Equation 15.59 applies to both pore-air and pore-water pres-
sures since capillary effects were ignored. The relationship
between a change in porosity and a change in total stress
can be established by combining the above two plots. For a
given change in porosity
n
, the change in total stress
σ
y
can be obtained by adding the magnitudes of
(σ
y
−
u
w
)
and
u
w
.
This summation procedure is repeated for several
changes in porosity until a curve of
n
versus
σ
y
is established.
The next step in the procedure is to cross-plot the pore-
water pressure
u
w
against the major principal stress
σ
y
,as
shown in Fig. 15.19. The initial values of
u
w
and
σ
y
can be
estimated. Hilf (1948) assumed that the initial pore-water
pressure was atmospheric. The pore-water pressure increase
due to total stress increase is obtained by cross-plotting
n
versus
u
w
and
n
versus
σ
y
. The magnitudes of
u
w
and the corresponding
σ
y
are then added to the initial
values of
u
w
and
σ
y
.
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