FLOOD05005

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: State Of Colorado Dam Safety Manual
• Date: 6/1/1983
• Prepared By: Colorado State Engineers Office
• Floodplain - Doc Type: Educational/Technical/Reference Information

6

Imagine that this sample is carefully sliced in half.
Placed under a powerful magnifier, the sliced sur-
face would look like that shown in Fignre 2.4-2.

d. NATURAL DEPOSIT
A sample of a natural deposit of soil can coni
combination of rock, gravel, sand, silt, and
It can also include some organic material al
course will contain air and water.

AIR AND
WATER

SURFACE OF
SAND SAMPLE

MAGNIFIED VIEW
FIGURE 2.4-2 SAND STRUCTURE
Sand particles occupy the largest portion of the
area viewed. Air and water occupy the remainder
of the area.

b. SILT
A silt material is prepared in a similar manner to
the sand. The structure will contain silt particles,
water and air. The sliced surface ofthe silt sample
under a powerful magnifier would appear much
like that shown below.

MAGNIFIED VIEW
FIGURE 2.4-5 STRUCTURE OF NATURAL DEPOSIT

These examples show that any soil deposit
tains water and air in addition to the solid
particles. The voids that are filled by the air
water provide pathways for water to flow thro
the soil. By reducing the number of voids, the
will contain fewer pathways for flow.

2.5

COMPACTION
The sand sample contains large amounts of water
air. The only change from its natural condition
adding water is the application of pressure by har.
What can be done to reduel: the amount of air a.
water in the sample to allow fewer spaces for flo!
Squeezing on it harder seems to be a logical answ.
that is, applying more pressure to the sample.

Applying greater pressure to the sample will redu
the amount of space available for air and water in tv
ways:

SURFACE OF
SILT SAMPLE

MAGNIFIED VIEW
FIGURE 2.4-3 SILT STRUCTURE
Again we see that the silt particles make up the
majority of the area but are interlaced with air
and water.

c. CLAY
A similarly prepared sample of clay must be
viewed under a microscope. We see that the clay
particles are interlaced with air and water.

I. The air between grains
reducing the void areas.

at

t t

can be squeezed OU

SURFACE OF
CLAY SAMPLE

8.6....
. -~
0.....
,\~li)

MAGNIFIED VIEW
FIGURE 2....4 CLAY STRUCTURE
Very small droplets of water and air bubbles take
up a portion of the area viewed.

FIGURE 2.5-1 REDUCING VOIDS

2. Fragments are broken offfrom some particles, 01
particles are deformed, allowing the void area tc
be reduced further.