Figure 15-29.-Varying sieve sizes.
3. Place three scoops (24 g) of reagent in the
cap. Then, with the pressure vessel in a horizon-
tal position, insert the cap into the pressure vessel
and tighten the clamp to seal the cap to the unit.
4. Raise the moisture tester to a vertical
position so that the reagent falls into the
vessel.
5. Hold the moisture tester horizontally;
vigorously shake the device with a rotating
motion for 10 sec to put the steel balls into orbit
around the inside circumference; then rest for 20
sec. Repeat the shake-rest cycle for a total of 3
min. Do not allow the steel balls to fall against
either the cap or orifice leading to the dial; this
may cause damage.
6. Holding the tester horizontally at eye level,
read and record the dial reading as the percent
of moisture by wet mass.
7. When the sample is dumped, examine it for
lumps. If the soil sample is not completely broken
down, increase the time limit (shaking unit) by
1 min on the next test.
8. To determine the percentage of moisture by
dry mass (ovendry moisture percentage), read the
direct reading obtained in No. 6 above into a
calibration curve that is also supplied with the test
set.
MECHANICAL ANALYSIS
Mechanical analysis is the determination of
grain sizes and the percentage distribution of each
size. A complete mechanical analysis is ac-
complished in two parts: sieve analysis and
hydrometer analysis.
Sieve Analysis
A sieve analysis is applicable to soils that are
larger than the No. 200 sieve or that contain small
amounts of material passing the No. 200 sieve.
You can conduct the sieve analysis either on the
entire sample or on the sample after the fines are
removed by prewashing. The apparatus and pro-
cedures used to conduct a sieve analysis are
described below.
APPARATUS.— Typical sieve analysis ap-
paratus includes a gram weighing balance and a
number of sieves with apertures of varying sizes
used to determine grain sizes (fig. 15-29). Sieves
may be of the ordinary circular SIFTER type
(usually about 8 in. in diameter) or the ROCKER
type, which consists of a rocker frame in which
screens with apertures of various sizes can be
placed.
The sieve used for analysis is the so-called stan-
dard sieve. A standard sieve has a square aper-
ture. Screen sizes are designated as follows: A
sieve with fewer than four apertures to the linear
inch is designated by the size of an aperture; for
example, a 1/4-in., 1/2-in., 3/4-in., or 1-in. sieve.
A sieve with four or more apertures to the
linear inch is designated by a number that
represents the number of apertures to the linear
inch. A No, 4 sieve, for example, has four aper-
tures to the linear inch, a No. 6 has six apertures,
and so on. The finest sieve used is a No. 200, with
200 apertures to the linear inch and an aperture
size slightly smaller than one two-hundredth of
an inch square.
To conduct a sieve analysis, you need
an electric or hand-operated sieve shaker.
15-21
