Humboldt H-4167 Voluvessel - Manual (Page 4)

on the volume indicator. Note and record the pressure. Depending upon
the type of apparatus, this pressure may be as high as 5 psi (34.5 kPA). It will
usually be necessary to add load (surcharge) to the apparatus to prevent it from
rising (Note 3). Note and record the total amount of load added. The difference
between the initial and the final readings of the volume indicator is the indicator
volume value for the container.
The membrane may be withdrawn from the container by applying a partial
vacuum to the liquid in the apparatus. Repeat the procedure for the other
containers.
Note 1:
If the calibration container or mold is airtight, it may be necessary to
provide an air escape, since the rubber membrane can entrap air within the
container and cause an erroneous volume measurement. After the volume of
the container has been determined with water and prior to the insertion of the
rubber balloon, small air escape holes may be provided by placing lengths of
small diamter string over the edge of the container and down inside the wall
slightly beyond the bottom center. This will permit air leakage during the filling
o the conter with the membrane. If such a procedure is necessay in the labora-
tory, it may be necessary to use a similar procedure on tightly-bonded soil in
the field.
Note 2:
Before any measurements are made, it may be necessary to distend the
rubber balloon and remove air bubbles adhering to the inside of the membrane
by kneading.
Note 3:
In field tests, additional loads (surcharge) will increase the stress in the
unsupported soil surrounding the test hole and will tend to cause it to deform.
Using a base plate may reduce the stress.