Geology Reference
In-Depth Information
it may be necessary to apply a downward load (surcharge) to the
apparatus to keep it from rising (Note 3). Record the readings, pres-
sures, and surcharge loads used. The difference between the initial
and final readings is the indicated volume. Determine the volumes
of the other molds or containers. A satisfactory calibration check of
an apparatus has been achieved when the difference between the
indicated and calibrated volume of the container or mold is 1%, or
less, for all volumes measured. Select the optimum operating pres-
sure and record it for use with the apparatus during field testing
operations.
Note 2
—Before any measurements are taken, it may be
necessary to distend the rubber balloon and, by kneading,
remove the air bubbles adhering to the inside of the membrane.
If the calibration castings or molds are airtight, it may be
necessary to provide an air escape to prevent erroneous
results caused by the trapping of air by the membrane. One
means of providing air escape is to place small diameter
strings over the edge of and down the inside, slightly beyond
bottom center of the mold or casting. This will allow trapped
air to escape during the measurement of the calibrated mold
or container.
Note 3
—It is recommended that the operating pressure of the
apparatus be kept as low as possible while maintaining the 1%
volume accuracy. The use of higher pressures than necessary
may require the use of an additional load or surcharge weight
to prevent uplift of the apparatus. The combined pressure and
surcharge loads may result in stressing the unsupported soil
surrounding the test hole, causing it to deform.
(4) Calculate the volume of the calibration containers or molds as
follows:
V
(
M
2
M
1
)
V
w
(15-1)
where:
V
volume of the container or mold, mL
M
2
mass of mold or container, glass, and water, g
M
1
mass of mold or container and glass, g
V
w
volume of water per gram based on temperature
taken from Table 15-1, mL/g
10
5
for ft
3
if needed
Note 4
—Multiply milliliters by 3.5315
for equipment usage.
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