Measuring Permeabilities of Soil, Sand, and Gravel

Grade Level: 6-8

Background

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.

Materials

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
  

Procedure

1. 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.
   
   
2. 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.
   
   
3. Put the cans into the pie pans. Pour 200 mL of water into each of the cans and let the cans sit overnight.
   
   
4. 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.
   
   
5. 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?
   
   
6. 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?