CS650 and CS655 Water Content Reflectometers
28
in microwave for 3 minutes, cooling in desiccator then weighing and
repeating this process until mass is constant.
h.
Weigh the container holding the dry soil, and subtract the container
weight from this value to get the dry soil mass.
i.
Record the dry soil mass.
j.
Repeat process to take replicate samples. Three carefully handled
samples provide good results.
9.
Calculate gravimetric water content from wet mass of sample (m
wet
) and
dry mass of sample (m
dry
):
θ
g
=
m
wet
−
m
dry
m
dry
For the bulk density,
ρ
bulk
=
m
dry
volume
cylinder
the dry mass of the sample is divided by the sample tube volume.
The volumetric water content is the product of the gravimetric water
content and the bulk density
θ
v
=
θ
g
•
ρ
bulk
The average water content for the replicates and the recorded CS650
period are one datum pair to be used for the calibration curve fit.
8.4.5 Calculations
The empty cylinders used for core sampling should be clean and both empty
mass and volume are measured and recorded. For a cylinder, the volume is
volume =
π
•
�
d
2
�
2
• h
where d is the inside diameter of the cylinder and h is the height of the
cylinder.
During soil sampling it is important that the cores be completely filled with soil
but not extend beyond the ends of the cylinder.
Once soil core samples are obtained, place the soil-filled cylinder in a small
tray of known empty mass. This tray holds the core sample during drying in an
oven.
To obtain m
wet
, subtract the cylinder empty mass and the container empty mass
from the mass of the soil filled cylinder in the tray. Remove all the soil from
the cylinder and place this soil in the tray. Dry the samples using oven or
microwave methods as described earlier.
