Geology Reference
In-Depth Information
The change in void ratio,
e
, can be computed by dividing change in
Δ
thickness (
H
) by height of solid in the specimen (
H
s
). The height of solid
in the specimen was determined previously (by dividing volume of solid
in the specimen by area of the specimen) to be 0.881 cm. Hence,
Δ
¢
H
H
s
0.0401
0.881
0.046
¢
e
Finally, the void ratio
e
for the
500 lb/ft
2
loading can be deter-
mined by subtracting the change in void ratio
e
from the initial void
Δ
ratio
e
0
. Hence,
e
e
0
¢
e
1.249
0.046
1.203
The values just computed are listed in the second row (correspond-
ing to
500 lb/ft
2
) of the data form on page 310. Each additional loading
on the test specimen will furnish a set of time-versus-deformation dial
readings, which through subsequent evaluation will provide a void
ratio
e
corresponding to a specific loading, or pressure,
p
. Such addi-
tional loadings (and subsequent analyses) would be listed in the
remaining rows of the data form. Although no laboratory data are given
herein for additional loadings on the test specimen, rows for loadings of
1,000, 2,000, 4,000, 8,000,
and
16,000 lb/ft
2
have been included on the
form on page 310 in order to demonstrate the complete evaluation of a
consolidation test.
Next a graph of pressure (the first column on page 310) along the
abscissa on a logarithmic scale versus void ratio (the last column on
page 310) along the ordinate on an arithmetic scale can be prepared.
This graph, which is known as the
e
- log
p
curve (i.e., void ratio versus
the logarithm of pressure), is one of the primary results of a consolida-
tion test. The
e
- log
p
curve for this example is shown in Figure 20-5.
[D] Coefficient of Consolidation, c
v
Recall that the equation for computing the coefficient of consolidation,
c
v
,is
0.196
H
2
t
50
(20-8)
c
v
As indicated previously, in the example under consideration,
t
50
, the time
required for 50% consolidation, is 8.2 min. The value of
H
, which is half the
thickness of the test specimen at 50% consolidation, can be determined as
follows:
H
1
>
2
[(initial height of specimen at beginning of test)
(deformation dial reading at 50% consolidation)]
H
1
2
(
0.780
0.0108)
0.385 in.
>
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