Measuring Permeabilities of Soil, Sand, and Gravel
Grade Level: 6-8
Source: Adapted with permission from an activity
D. Whisonant, Physical Science Department,
Radford University, Radford,
SEPM (Society for Sedimentary Geology), 2006.
This investigation will help you to learn that different geologic materials
have different characteristics. Why is this important? When a road or
building is constructed, the underlying substance could have an effect
on the structure's stability. Different soils, for instance, can pose
different problems, based on climate, topography, and amount of rainfall
in the area. Clay-poor soils are preferred over clay-rich soils for this
reason: when water is absorbed, the clays swell, the soils expand, and
pressure may be exerted on building foundations. Enough pressure could
cause foundations to crack.
For this activity, your teacher might provide the soil samples you will
test. Or you, as a citizen scientist, might bring in samples from your
own yard or garden.
For a group of four:
- 4 metal cans (coffee can size works well) with several holes punched
in the bottom
- Pie pans or other containers to catch water under metal cans
- 250 mL beaker or similar container
- 100 mL graduated cylinder
- Sand, gravel, and soil samples with different characteristics
- Ice-cream sticks or similar materials to construct a small wall
- Masking tape and markers to label the cans
- Magnifying glass or dissecting microscope
- Notebook to record observations
- Use the magnifier to examine the particles that make up each of the
materials. How are the particles different in shape and size? Based
on your observations, predict which material might allow water to flow
through it most freely and least freely. Record your predictions and
your reasons for the predictions.
- Fill the four cans, each with a different material, such as sand,
gravel, mud, or another soil. Don't compact the material; just put it
in loosely to the same height in each can. Label the cans with masking
tape and markers.
- Put the cans into the pie pans. Pour 200 mL of water into each of
the cans and let the cans sit overnight.
- The next day, measure the water collected from each can in the graduated
cylinder. Compare the amount of water that flowed from each can into
the corresponding pie pan. Which material did a lot of water flow through?
Which material did little water flow through? How much water was absorbed
by each material? Record the results.
- Repeat the entire investigation, but this time, compact the materials
in the cans before adding the water. How did the results from the compacted
materials compare to those from the uncompacted materials?
- How could you explain the different permeabilities of the materials
in terms of the grain sizes of the materials? Which would you choose
to use under the foundation of a house and why? Would you use compacted
or uncompacted material and why?