Geology Reference
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[C] Void Ratio
H , can
be computed by subtracting the initial deformation dial reading at the
beginning of the very first loading from the deformation dial readings
corresponding to 100% primary consolidation for each respective load-
ing. The change in void ratio for each loading,
The change in thickness of the specimen for each loading,
Δ
e , can then be calculated
by dividing each change in thickness of the specimen (
Δ
H ) by the height
Δ
H/H s . The void ratio for each
loading, e , can be determined by subtracting the change in void ratio (
of solid in the specimen ( H s ); hence,
e =
Δ
Δ
e )
Δ
from the initial void ratio, e 0 ; hence, e = e 0 -
e .
Values of void ratio for each loading, along with respective applied
pressures, can be used to plot the required graph of void ratios versus
the logarithm of pressure ( e - log p curve).
Δ
[D] Coefficient of Consolidation
For each load increment for which time-versus-deformation readings
were obtained, the coefficient of consolidation can be calculated using
the equation
0.196 H 2
t 50
(20-8)
c v
where:
c v
coefficient of consolidation, in. 2 /min
H
half the thickness of the test specimen at 50% consoli-
dation (because the specimen is drained on both top
and bottom in this test), in.
t 50
time to reach 50% consolidation, min
It should be emphasized that a determination of the coefficient of
consolidation must be made for each test loading. The values of coeffi-
cient of consolidation for each loading, together with corresponding
applied pressures, can be used to plot the required graph of coefficient
of consolidation versus the logarithm of pressure ( c v - log p curve).
A consolidation test was performed in the laboratory, and the following
data were obtained:
NUMERICAL
EXAMPLE
[A] Specimen Data
At beginning of test:
Diameter of specimen, D
2.50 in.
Initial height of specimen, H 0
0.780 in. (i.e., 1.981 cm )
Mass of specimen ring plus specimen
208.48 g
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