2. Assignment#3
Grain Size Distribution Analysis
METHODOLOGY & PROCEDURES FOR DETERMINING SEDIMENT GRAIN SIZE
DISTRIBUTION
Sample Preparation
1. Pour ~ 100g of sediment from the sample bag into a 400mL beaker and label
beaker with the sediment number or naming convention.
2. Allow ~100g sample to dry in oven at 105º C or air dry over the course of a
couple days. Complete dryness is necessary for an accurate mass (explained
in Step 5).
3. Using a small pestle and mortar, thoroughly grind dried sediment till all large
particle clumps are separated into individual grains.
4. Using a digital scale, weigh one 600mL beaker for each sample. Make sure
the beaker is completely dry and labeled to ensure the correct sediment
is placed in this beaker.
5. Using a spoon and being careful to spill sediment only into beaker, pour
exactly 50g of sediment out of the mortar and pestle into the beaker. The beaker
should be resting on the digital scale during this step and care must be given
to not spill excess sediment onto the scale itself, ...only in the beaker. The
remainder of the sediment can be added back to the original sample bag, if
desired.
6. Add 250mL of distilled water to the 50g of sediment.
7. Add 100mL of sodium hexametaphosphate ((NaPO3)6) to the sediment and
distilled water. This chemical is a deflocculating agent, which aids in the
separation of clays into individual particles.
8. Using a spoon, stir mixture thoroughly.
9. Pour sample into a milk shake container. Use a squeeze bottle of distilled to
ensure all sediment is transferred from the 600mL beaker to the container.
(From now on, use the squeeze bottle of distilled water during each transfer
3. to ensure all sediment is accounted for.) Mix with a milk shake mixer on low
power for 5-7 minutes.
10. Pour back into 600 mL beaker (or 1000mL beaker if more room is needed).
Again, make sure the beaker is labeled correctly. Let sample sit overnight
to allow for chemical deflocculation.
Hydrometer Analysis
1. Transfer sample from 600mL beaker to a 1000mL Bouyoucos tube. Fill with
distilled water to the fill line. The top of the meniscus should reach the fill
line.
2. Fill another Bouyoucos tube with only distilled water. Insert a thermometer
into the water and record the control temperature. Using the hydrometer
that will be used for the analysis, place it (large end first) into the tube.
Allow the hydrometer to stabilize and record the specific gravity. The
measurement should be read at the top of the meniscus. This is the control
measurement and it should be taken periodically throughout the hydrometer
analysis.
3. Have a watch with seconds and the hydrometer close at hand.
4. Use a synthetic stopper to cap off the Bouyoucos tube with the sediment
sample. Turn the tube upside down and again right side up, using both hands at
each end of the tube and continue this for 1 minute. This ensures complete
mixing of the sediment sample.
5. As soon as the Bouyoucos tube is placed on the table, the watch should be
read and all time intervals at which a hydrometer reading is
required will be extended from this time. It is a good idea to make sure the
tube is placed down at a hh:mm:00 time (i.e. 3:45:00).
6. At each measurement time, the hydrometer should be slowly placed into
and slowly removed from the solution. The hydrometer should be read at the
following times after the tube is set down :
45sec, 1min, 90sec, 3min, 5min, 10min, 15min, 30min, 45min, 1hr, 2hr, 4hr,
6hr, 1day, 2day
Once again, control temperatures and specific gravity readings should be
periodically read during the analysis, especially as the time intervals are spread
further apart.
4. Wet Sieve Analysis
1. Obtain 5 sieves of the following mesh #'s:
U.S. Standard Mesh #18 (0 phi) ; very coarse sand
U.S. Standard Mesh #35 (1 phi) ; coarse sand
U.S. Standard Mesh #60 (2 phi) ; medium sand
U.S. Standard Mesh #120 (3 phi) ; fine sand
U.S. Standard Mesh #230 (4 phi) ; very fine sand
