Figure 15-5.-Obtaining individual bag samples.
along a row in correct order, as shown in figure
15-5.
Composite Samples
A composite sample is a representative mix-
ture of all soil within a soil mass to be investigated
or of the material contained in a stockpile or wind-
row of soil excavated from a trench. A test sam-
ple is obtained from a composite sample by
quartering (to be explained later) in the
laboratory.
To take composite samples from test pits, tren-
ches, or power shovel cuts, take the following
steps:
1. Remove any overburden or surface soil that
is to be wasted.
2. Shave off loose and dried soil to ob-
tain a fresh surface for taking the sam-
ple.
3. Excavate a channel of uniform cross
section from top to bottom, and deposit the soil
onto a quartering cloth, canvas, or tarpaulin, as
shown in figure 15-6.
Figure 15-6.-Taking a composite sample with an exposed
face.
Collect and bag all material removed to
ensure that the sample contains the correct
proportions. To take composite samples from
auger holes,
collect all material excavated
from the hole after first removing the over-
burden. When taking representative composite
samples from stockpiles or large windrows,
take particular care. When material is dumped
on large piles,
the coarse material tends
to roll to the bottom, leaving the finer
material on the top. To compensate for
this, take the sample from a full height
strip after clearing the surface. To sample
from a small windrow, excavate and bag mate-
rial from a short section, as shown in figure
15-7.
Moisture Content Samples
The natural moisture content of soil is deter-
mined from samples taken in the field and placed
in a container, which is then sealed to prevent loss
of moisture by evaporation. Natural moisture
content determinations are valuable in interpreting
information obtained from test borings or pits,
15-10
