Environmental Engineering Reference
In-Depth Information
Gage, air pressure
Air
supply
Water
meter
Valves
Pressure
gages
Water
pump
Air hose
Inner and outer pipes
for water supply
(or single pipe for
packer testing only)
Drop pipes
Expandable rubber
sleeve
(Packer length
approximately 5
times boring
diameter)
Perforated outer pipe
to test between
packers
(Inner pipe provides
water to test
below packers)
Air hose to
lower packer
Upper packer
Test section
Lower packer
Lower test
section
Inner pipe
(unperforated)
to test lower
section
FIGURE 3.17
Apparatus for determining rock permeability
in situ
using pressure testing between packers.
pressure above the natural piezoelectric level should not exceed 1 psi for each
foot (23 kPa/m) of soil and rock above the upper packer.
Data Evaluation
Curves of flow vs. pressure are plotted to permit evaluation of changes in the rock mass
during testing:
Concave-upward curves indicate that fractures are opening under pressure.
●
Convex curves indicate that fractures are being clogged (permeability decreasing
with increased pressure).
●
Linear variation indicates that no change is occurring in the fractures.
●
Approximate values for
k
are computed from the expressions (USBR, 1974)
k
(
Q
/2
π
LH
)(ln
L
/
r
) for
L
10
r
(3.8)
k
(
Q
/2
π
LH
) sinh
1
(
L
/2
r
) for 10
r
L
r
(3.9)
where
k
is the coefficient of permeability,
Q
the constant flow rate in the hole,
L
the length
of the test section,
H
the differential head on the test section (see explanation below),
r
the
hole radius and sinh
-1
the inverse hyperbolic sine.
