Quicksand Danger: Myth or Reality?
Image 1. Four students set up the first iteration of their quicksand experiment over a laboratory sink.Copyright 2018 J. Patrick Coughlin, CC BY-SA 4.0, University of Colorado Denver
Students explore the physical science behind the causes of quicksand and become familiar with relationship between concepts such as total stress, pore pressure, and effective stress. Students also relate these concepts to soil liquefaction—a major concern during earthquakes. Students begin the activity by designing a simple device to test the effects of quicksand on materials of different densities and weights. They prototype a support structure that works to prevent a heavy object from sinking into quicksand. At the end of the activity, students reflect on the engineering design process and consider the steps civil engineers take in designing sturdy buildings and other structures.
In regions of the world subject to earthquakes, civil engineers must consider how well a building, as well as the ground upon which it sits, can withstand seismic waves. The potential for soil liquefaction, a condition of stress in which solid ground can behave like a liquid, is a major consideration in civil engineering. One example is the extensive liquefaction that occurred during the 1964 Niigata earthquake in Japan. Much of Niigata had been built on loose sand from ancient river beds and many buildings sunk into the ground because of the earthquake (see Image 2). Studying the relationship between concepts such as total stress, pore pressure, and effective stress in liquefaction help engineers understand how to design structures that can withstand major seismic activity. By using quicksand as a model, engineers can advance their understanding of foundational soils and prevent structural damage—and the loss of life from such damage—due to liquefaction.
Image 2. Widespread damage as a result of soil liquefaction during the 1964 Niigata earthquake in Japan.Copyright 1964 Ungtss, Public Domain Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Liquefaction_at_Niigata.JPG
After this activity, students should be able to:
- Explain the relationship between soil and water in quicksand and soil liquefaction.
- Create a model testing device to test the question: “Would humans sink in quicksand?”
- Design and test a model structure to prevent objects from sinking in quicksand.