Geology Reference
In-Depth Information
[B] Permeability Test
The coefficient of permeability can be evaluated by modifying Eq. (18-2),
(18-2)
q
kiA
In the experimental procedure, the value of
i
, the gradient, can be
replaced by
h/L
, where
h
is the head (difference in manometer levels)
and
L
is the length between manometer outlets. Additionally, the value
of
q
, the rate of water flow, can be replaced by
Q/t
, where
Q
is the quan-
tity (volume) of water discharged and
t
the time required for that quan-
tity to be discharged. If these substitutions are made in Eq. (18-2) and
the resulting equation solved for
k
, the result is [1]
QL
Ath
(18-3)
k
where:
k
coefficient of permeability, cm/s
Q
quantity (volume) of water discharged during test, cm
3
L
length between manometer outlets, cm
A
cross-sectional area of specimen, cm
2
t
time required for quantity
Q
to be discharged during
test, s
head (difference in manometer levels) during test, cm
The permeability computed using Eq. (18-3) is the value for the
particular water temperature at which the test was conducted. It is nec-
essary to correct this permeability to that for 20°C by multiplying the
computed value by the ratio of viscosity of water at the test temperature
to viscosity of water at 20°C (see Table 18-2).
h
A laboratory test was conducted according to the procedure described
previously. The following data were obtained:
NUMERICAL
EXAMPLE
Diameter of specimen,
D
10.16 cm
Length between manometer outlets,
L
11.43 cm
Height,
H
1
20.0 cm
Height,
H
2
4.5 cm
For water content determination:
Mass of air-dried soil plus can
299.41 g
Mass of oven-dried soil plus can
295.82 g
59.39 g
Mass of air-dried soil before compaction,
M
1
Mass of can
3,200.0 g
Mass of unused remaining portion of air-dried soil after com-
paction,
M
2
1,102.5 g
Manometer readings,
h
1
and
h
2
10.9 cm
and
5.4 cm
(same
manometer readings for each of three trials)
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