Soapy Stress
This rock surface is broken from tensional stress. You can tell because it looks like it is being pulled apart.Copyright National Park Service http://www.nps.gov/crmo/glossary/pressure-ridge.jpg
To experience the three types of material stress related to rocks—tensional, compressional and shear—students break bars of soap using only their hands. They apply force created by the muscles in their own hands to put pressure on the soap, a model for the larger scale, real-world phenomena that forms, shapes and moves the rocks of our planet. They also learn the real-life implications of understanding stress in rocks, both for predicting natural hazards and building safe structures.
Geotechnical engineers are concerned with the properties of earth materials. Their understanding of how rock behaves under stress is important for safety in our modern world. Engineers investigate above and below ground rock and soil to determine its characteristics, and then design foundations for human-made structures, such as bridges and stadiums. Their expertise helps build secure foundations for structures such as footings, piles, drilled piers and retaining walls. Their knowledge assures well-built dams, embankments, levees, mines and tunnels—all structures built with or in rocks and soil. Engineers also apply their expertise to assess the natural hazards risk to humans, property and the environment.
After this activity, students should be able to:
- Describe stress as it relates to materials, such as rocks.
- Identify and distinguish between the three types of stress.
- Describe why engineers must understand the properties of earth materials.