CS616 and CS625 Water Content Reflectometers
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surrounded by soil. Movement of rods from side-to-side during insertion
can form air voids around rod surface and lead to measurement error.
Collect the probe output period. Repeat previous step and this step 3 or 4
times.
Determine volumetric water content by subsampling soil column after
removing probe or using weight of column. If subsampling is used,
remove soil from column and remix with samples used for water content
measurement. Repack column.
Water can then be added to the top of the container. It must be allowed to
equilibrate. Cover the container during equilibration to prevent
evaporation. The time required for equilibration depends on the amount of
water added and the hydraulic properties of the soil. Equilibration can be
verified by frequently observing the CS616/CS625 period output. When
period is constant, equilibration is achieved. Collect a set of calibration
data values and repeat the water addition procedure again if needed.
With soil at equilibrium, record the CS616/CS625 period value.
Take subsamples of the soil using containers of known volume. This is
necessary for measurement of bulk density. Copper tubing of diameter
1 inch and length about 2 inches works well. The tubes can be pressed
into the soil surface.
It is good to take replicate samples. Three carefully handled samples will
provide good results.
The sample tubes should be pushed evenly into the soil. Remove the tube
and sample and gently trim the ends of excess soil. Remove excess soil
from outside of tube.
Remove all the soil from tube to a tray or container of known weight that
can be put in oven or microwave. Weigh and record the wet soil weight.
Water is removed from the sample by heating with oven or microwave.
Oven drying requires 24 hours at 105 °C. Microwave drying typically
takes 20 minutes depending on microwave power and sample water
content. ASTM Method D4643-93 requires heating in microwave for 3
minutes, cooling in desiccator then weighing and repeating this process
until weigh is constant.
Gravimetric water content is calculated after the container weight is
accounted for.
g
wet
dry
dry
m
m
m
